ELECTRONIC DEVICESAssist prof Laura-Nicoleta IVANCIU PhD

C12 ndash BJT operation

2Laura-Nicoleta IVANCIU Electronic devices

Contents

Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

C12 ndash BJT operation

3Laura-Nicoleta IVANCIU Electronic devices

Transistors = active semiconductor devices with three terminals - used to amplify or switch signals - essential components of electronic circuits- discrete or integrated

Operating principleThe voltage applied between two terminals (command)

controls the current through the third terminal

C12 ndash BJT operation

Previously on ED (C11)

4Laura-Nicoleta IVANCIU Electronic devices

pnpnpn

C12 ndash BJT operation Simplified structure of a BJT

5Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Simplified structure of a BJT

The transistor effect consists in a current flowing through a reverse biased junction (B-C) due to its interaction with a forward biased junction (B-E) placed in its very close vicinity

For the transistor effectbull base region - very thin considerably thinner than the diffusion length of the minority carriers in the base regionbull emitter region - more doped than the base regionbull emitter and collector regions - wider than the diffusion length of the minority carriers in these regions

npn

6Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input characteristic

T

BEVv

SB eIi

β=

IS - saturation current (~ nA - pA)

qKTVT = thermal voltage C20mV25 O=TV

β current gain (~ tens hundreds dimensionless)

7Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Transfer characteristic

T

BEVv

SC eIi =

BC ii β=

8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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2Laura-Nicoleta IVANCIU Electronic devices

Contents

Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

C12 ndash BJT operation

3Laura-Nicoleta IVANCIU Electronic devices

Transistors = active semiconductor devices with three terminals - used to amplify or switch signals - essential components of electronic circuits- discrete or integrated

Operating principleThe voltage applied between two terminals (command)

controls the current through the third terminal

C12 ndash BJT operation

Previously on ED (C11)

4Laura-Nicoleta IVANCIU Electronic devices

pnpnpn

C12 ndash BJT operation Simplified structure of a BJT

5Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Simplified structure of a BJT

The transistor effect consists in a current flowing through a reverse biased junction (B-C) due to its interaction with a forward biased junction (B-E) placed in its very close vicinity

For the transistor effectbull base region - very thin considerably thinner than the diffusion length of the minority carriers in the base regionbull emitter region - more doped than the base regionbull emitter and collector regions - wider than the diffusion length of the minority carriers in these regions

npn

6Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input characteristic

T

BEVv

SB eIi

β=

IS - saturation current (~ nA - pA)

qKTVT = thermal voltage C20mV25 O=TV

β current gain (~ tens hundreds dimensionless)

7Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Transfer characteristic

T

BEVv

SC eIi =

BC ii β=

8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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• Slide Number 19
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• Slide Number 21
• Slide Number 22
• Slide Number 23
• Slide Number 24

3Laura-Nicoleta IVANCIU Electronic devices

Transistors = active semiconductor devices with three terminals - used to amplify or switch signals - essential components of electronic circuits- discrete or integrated

Operating principleThe voltage applied between two terminals (command)

controls the current through the third terminal

C12 ndash BJT operation

Previously on ED (C11)

4Laura-Nicoleta IVANCIU Electronic devices

pnpnpn

C12 ndash BJT operation Simplified structure of a BJT

5Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Simplified structure of a BJT

The transistor effect consists in a current flowing through a reverse biased junction (B-C) due to its interaction with a forward biased junction (B-E) placed in its very close vicinity

For the transistor effectbull base region - very thin considerably thinner than the diffusion length of the minority carriers in the base regionbull emitter region - more doped than the base regionbull emitter and collector regions - wider than the diffusion length of the minority carriers in these regions

npn

6Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input characteristic

T

BEVv

SB eIi

β=

IS - saturation current (~ nA - pA)

qKTVT = thermal voltage C20mV25 O=TV

β current gain (~ tens hundreds dimensionless)

7Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Transfer characteristic

T

BEVv

SC eIi =

BC ii β=

8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

• Slide Number 1
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4Laura-Nicoleta IVANCIU Electronic devices

pnpnpn

C12 ndash BJT operation Simplified structure of a BJT

5Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Simplified structure of a BJT

The transistor effect consists in a current flowing through a reverse biased junction (B-C) due to its interaction with a forward biased junction (B-E) placed in its very close vicinity

For the transistor effectbull base region - very thin considerably thinner than the diffusion length of the minority carriers in the base regionbull emitter region - more doped than the base regionbull emitter and collector regions - wider than the diffusion length of the minority carriers in these regions

npn

6Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input characteristic

T

BEVv

SB eIi

β=

IS - saturation current (~ nA - pA)

qKTVT = thermal voltage C20mV25 O=TV

β current gain (~ tens hundreds dimensionless)

7Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Transfer characteristic

T

BEVv

SC eIi =

BC ii β=

8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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• Slide Number 22
• Slide Number 23
• Slide Number 24

5Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Simplified structure of a BJT

The transistor effect consists in a current flowing through a reverse biased junction (B-C) due to its interaction with a forward biased junction (B-E) placed in its very close vicinity

For the transistor effectbull base region - very thin considerably thinner than the diffusion length of the minority carriers in the base regionbull emitter region - more doped than the base regionbull emitter and collector regions - wider than the diffusion length of the minority carriers in these regions

npn

6Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input characteristic

T

BEVv

SB eIi

β=

IS - saturation current (~ nA - pA)

qKTVT = thermal voltage C20mV25 O=TV

β current gain (~ tens hundreds dimensionless)

7Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Transfer characteristic

T

BEVv

SC eIi =

BC ii β=

8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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• Slide Number 23
• Slide Number 24

6Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input characteristic

T

BEVv

SB eIi

β=

IS - saturation current (~ nA - pA)

qKTVT = thermal voltage C20mV25 O=TV

β current gain (~ tens hundreds dimensionless)

7Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Transfer characteristic

T

BEVv

SC eIi =

BC ii β=

8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

• Slide Number 1
• Slide Number 2
• Slide Number 3
• Slide Number 4
• Slide Number 5
• Slide Number 6
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• Slide Number 24

7Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Transfer characteristic

T

BEVv

SC eIi =

BC ii β=

8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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8Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Input and transfer characteristics npn BJT

Input and transfer characteristics

BC ii β=T

BEVv

SB eIi

β= T

BEVv

SC eIi =

9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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9Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Output characteristics npn BJT

Family of output characteristics

Active region (aF)iC = βiB

Saturation region (exc)iC lt βiBVCEsat asymp 02V

Cutoff region (off)iC = iB =0

T

BEVv

SC eIi =

IS = 210-15 Aβ = 100

10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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10Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Operating regions npn BJT

vBE lt 06 V vBC lt 06 V

vBE gt 06VvBC lt 06V

vBE gt 06VvBC gt 06Vrarely used

Note the transistor shouldnrsquot be biased very close to the origin of the axes or to one of the axis

Modes of useswitching mode (off) (exc)as an amplifier (aF) possibly (aR)

11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

• Slide Number 1
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11Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Currents

iE = iC + iB

In the active region (aF)iC = βiB )11(1

ββ+=+= CCCE iiii

iE = (β+1) iB asymp βiB

In the saturation region (exc) iC lt βiB

iE asympiC

Always valid regardless of operating region

12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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12Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Currents Limiting the command current

Limiting the command current

V70asympBEv

Command voltage is applied between B and E so command current is IB Limit IB by using a series resistance in B or E

13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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13Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation BJT saturation

resistors and applied voltages are chosen based on the desired region (off aF or exc) of the BJT

BJT can also be seen as a current-controlled current source (iC = βiB) when operating in the active region (aF)

βCex

Bsati

i =Boundary (aF) - (exc)

C

PS

C

CEsatPSCex R

vR

vVi asympminus

=

14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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14Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q is defined by VCE and IC

Q(VCE IC) is at the intersection between the load line and the output characteristic corresponding to vBE

Load linevCE = VPS - RC iC

15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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15Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation Quiescent point of the BJT

Quiescent point Q = a point on the output characteristic iC(vCE) of the BJT

Q2(VCE2 IC2) B

BECoB R

vvi minus= BC ii β=

CCPSCE iRVv sdotminus=

Load line

VPS

VPSRC

(exc)

Icex

16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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16Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Find the operating region and compute Q(VCE IC) for RB = 50 kΩ andi) vCo = 04 V ii) vCo = 17 V iii) vCo= 5 V

Examples

17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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17Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioni) because vCo= 04 V lt VThn = 06 V T - (off)

Q(VCE IC) = Q(12 V 0 mA)

ii) vCo gtVTh rArr T is on in (aF) or in (exc) Assume vBE = 07 V for conduction and β = 100 Assume T in (aF) so that iC = βiB Compare iB with iCex β

If iB gt iCex β the assumption was false and T is in (exc) If iB lt iCex β the assumption was true and T is in (aF)

Examples

18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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18Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solution

mA952

2012=

minus=

minus=

C

CEsatPSCex R

vVi

mA02050

7071=

minus=

minus=

B

BECoB R

vvi

mAiCex 0590100

95==

β

Because iB = 20 μA lt iCex β = 59 μA rArr T is in (aF)

V60V37870 ltminus=minus=minus= CEBEBC vvv

mA2020100 =sdot== BC ii β

V82212 =sdotminus=minus= CCAlCE iRVv)mA2V8(Q

Examples

19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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19Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 1

Solutioniii) mA0860

50705=

minus=

minus=

B

BECoB R

vvi

Because iB = 86 microA gt iCex β = 59 μA rArr T is in (exc)

vBEsat asymp 08V vBC = vBEsat - vCEsat asymp 08 V - 02 V = 06 V = VThn

Alternative method assume T in (aF) rArr iC = βiB = 86 mA

vCE = VPS - RCmiddotiC = 12 - 2middot86 = -52V

But vCE can only be positive so the assumption is false rArr T is in (exc)

mA95V20

====

CexC

CEsatCE

iIvV

Q(02 V 59 mA)

Examples

20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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20Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

β = 100vBEon = 07 V

a) Find Q(VCE IC)b) What is the operating region of T

Examples

21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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21Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a) Since IB ltlt IC and IE = Ic + IBIC = IE

VRB2 ndash obtained from the voltage divider between RB1 and RB2 out of VCC

Examples

22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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22Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

a)

Q(425 V 215 mA)

Examples

33 1051015215 minusminus=CEV

23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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23Laura-Nicoleta IVANCIU Electronic devices

C12 ndash BJT operation

Example - 2

Solution

b) vCo = VRB2 gtvBEon rArr T is on in (aF) or in (exc)

Assume T in (aF)Compare iC with iCex

If iC gt iCex the assumption was false and T is in (exc) If iC lt iCex the assumption was true and T is in (aF)

mAkk

ICex 962105

81423

20153 =sdot

=+minus

=

215 mA lt 296 mA T is in (aF)rArrEC

CEsatCCCex RR

VVI+minus

=

Examples

24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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24Laura-Nicoleta IVANCIU Electronic devices

SummaryThe BJT (almost) holds no secrets from us after investigating Simplified structure of a BJT Input and transfer characteristics npn BJT Operating regions Currents Limiting the command current BJT saturation Quiescent point of the BJT Examples

Next week MOSFET operationTo do Homework 9

C12 ndash BJT operation

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