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MAE156A
October 17, 2006UCSD
H. Ali Razavi
M
Permanent DC Motor
After http://www.aosmithmotors.com/pdf/brochures/bulletin3100/ACDC.PDF
Coil (modeled: ) L
Resistance (modeled: ) R
dt
diLLV
iRRV Electro Motive ForceGenerator (modeled: )
VKEMFV VK
Electrical to Mechanical Conversion (modeled: ) TK
Model:
V
0
iRV
iTKT
dt
diLiRV
Kdt
diLiRV
Kirchhoff's Voltage law: 0 Kdt
diLiRV
iTKT
Kdt
diLiRV
R
KVTKT
dt
di 0- Steady State:
R
VTKT 0- Stall/Start:
Maximum TorqueUnder voltageV
For fixed linear relationshipbetween & T
V
- Power output:
R
KVTKTP
- Efficiency:ActualVi
T
TP
[n.m] T
[rad/sec]
A typical permanent magnet DC motor curve (copied from an actual spec sheet):
Measured at specific constant voltage:V
VI
T
Stall/Start Current
No Load Current
:Output Power
:Efficiency
:Measured Current
:Measured data points ,TNo Load Speed
Stall/Start Torque
Design Example: 9A +Margin: 10A
Design Example: 1.5A +Margin: 2A
PMMotor
10A: Start/Stall2A: ContinuousV: 10-12V
Design Example 1:
Objective: To Turn On and Off a Permanent Magnet DC motor using a Micro Processor with the requirement of passing 10A during On Time with 10-12V on motor terminals.
Problem 1: 10A is too high current to be provided by Microprocessor
Problem 2: Switching it off and on using microprocessor
Problem 3: Interfacing components and programming
Pin x
Microprocessor
Idea 1: Use of MOSFET to switch the Motor On/Off
Idea 2: Use of Bipolar Transistor to switch the Motor On/Off
Concept Generation
Risk Reduction
Trouble Shooting
Optimization
Problems Definition
Concept Generation
Idea 3: Use of Darlington Transistor to switch the Motor On/Off
# of components
Design Merits
CostPower (Start/Stall)
Power (Continuous)Efficiency (Start/Stall)
Efficiency (Continuous)
Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design
* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.414-417)
… Design Example 1:
Risk Reduction: Analysis of Idea 1
PMMotor
Pin x
Microprocessor
MD
S
G
External Supply
Solving Problem 1
Problem 2(needs further detail)
Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.)
* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.414-417)
… Design Example 1:
… Risk Reduction: Analysis of Idea 1
PMMotor
MD
S
G
External Supply
- This is an nMOSFET
- One can look catalog under “Power nMOSFET”
- http://www.fairchildsemi.com/
- Search “Power MOSFET”
- Picked “HUF764323D”
Step 3. Downloaded and Reviewed Spec sheet
Step 4. Analysis to determine - : required voltage to turn On - : the external voltage - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Power
… Design Example 1:
… Risk Reduction: Analysis of Idea 1
Case 1: Continuous Mode Operation (2A current through motor)
V12ddV
PMMotor
MD
S
GggV
ssV
ggV
ddV
ssV
TorqueSpeed
Eff
Thermal waste at MOSFET
External Supply
Case 2: Start/Stall Mode Operation (10A current through motor)
HUF764323D
VΩA
VΩA
6.1104.01012
92.1104.021212 DSRDSIDSVddVssV √Good! 10-12V on motor terminals.
The objective is to have 10-12V on motor terminals, so assume and verify if it would workV12ddV
P
Step 4. Analysis to determine - : required voltage to turn On - - - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Power
… Design Example 1:
… Risk Reduction: Analysis of Idea 1
Case 1: Continuous Mode Operation (2A current through motor)
V12ddV
PMMotor
MD
S
GggV
ssV
ggV
ddV
ssVEff
Thermal waste at MOSFET
External Supply
Case 2: Start/Stall Mode Operation (10A current through motor)
HUF764323D
Continuous Efficiency
√√
%7.96
12
6.11
%3.9912
92.11
ddVssV
DIddVDIDSVDIddVEff
Stall/Start Efficiency
P
W
W
1201012
24212DIddVP
Continuous Power
Stall/Start Power
Step 4. Analysis to determine - : required voltage to turn On - - - -
… Design Example 1:
… Risk Reduction: Analysis of Idea 1
Case 1: Continuous Mode Operation (2A current through motor)
V12ddV
PMMotor
MD
S
GggV
ssV
ggV
ddV
ssVEff
External Supply
Case 2: Start/Stall Mode Operation (10A current through motor)
HUF764323D
√√
P√√
Assuming 25◦C Junction Temperature
V5.4ggVOverdrive for uncertainty
V
V
15.3
75.2ggV
Continuous Power
Stall/Start Power
Good! Microprocessor Can directly turn it On.
… Step 4. Analysis
… Design Example 1:
… Risk Reduction: Analysis of Idea 1
PMMotor
Pin x
Microprocessor MD
S
G
External Supply
Problem 1: Solved
Problem 2: Solved
V12
%7.96lStart/StalEff
%3.99ContinuousEff
Pull down resistoris added to preventpin floating and accidental turn onof motor.Desire: Small leakagecurrent.
MA0.1
V5
5
M5 HUF764323D
… Step 4. Analysis
… Design Example 1:
… Risk Reduction: Analysis of Idea 1
PMMotor
Pin x
Microprocessor MD
S
G
External SupplyV12
%7.96lStart/StalEff
%3.99ContinuousEff
M5
Design merits of Idea 1:
Cost= $A
# of Components = 2
HUF764323D
WlStart/Stal 120P
WContinuous 24P
Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design
* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408)
… Design Example 1:
Risk Reduction: Analysis of Idea 2
PMMotor
Pin x
Microprocessor
External Supply
Solving Problem 1
Problem 2(needs further detail) BI
BIFEh
To protect against reversecurrent[Note this was build in for nMOSFET]
To limit current and protect transistor
- This is an NPN Bipolar Transistor
- Download “Bipolar Power Transistor Selection Guide” from
- http://www.fairchildsemi.com/
- Looked in column under General Purpose Transistors
- Picked “KSH3055” with
Step 3. Downloaded and Reviewed Spec sheet
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.)
- (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408) - Looked at in the spec sheet of Chips it returned (to select a high gain transistor)FEh
FEh
10020 FEh
PMMotor
External Supply
Solving Problem 1
BI
BIFEh
IN4002
KSH3055
Standard Diode
PMMotor
External Supply
Solving Problem 1
BI
BIFEh
IN4002
KSH3055
Step 4. Analysis to determine - : required current to turn On - : the external voltage - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
BI
CV
EV
TorqueSpeed
Eff
Thermal waste at Bipolar TransistorCase 1: Continuous Mode Operation (2A current through motor)
Case 2: Start/Stall Mode Operation (10A current through motor)
AA
AA
Overdrive
AA
AA
2.110
10
05.050
2
110
10
04.050
2
1FEhEI
BIBIFEhBIFEhEI
EI
Continuous
Stall/Start
The objective is to have 10-12V on motor terminals, so assume and verify if it would workV12CV
CV
EV
Typical Characteristic
BR
BR
PMMotor
External Supply
Solving Problem 1
BIFEh
IN4002
KSH3055
Case 1: Continuous Mode Operation (2A current through motor)
Case 2: Start/Stall Mode Operation (10A current through motor)
EI
√√
V12CV
VsatCEA 2.02 VCI
V-
V-satCE 0.110.112
8.112.012VCVEV
Typical Characteristic
VsatCEA 110 VCI
Continuous
Stall/Start√ Good! 10-12V on motor terminals.
Step 4. Analysis to determine - - - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
BI
CV
EV
TorqueSpeed
Eff
Thermal waste at Bipolar Transistor
BI
BR
BR
Step 4. Analysis to determine - - - - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor
PMMotor
External Supply
Solving Problem 1
BIFEh
IN4002
KSH3055
Case 1: Continuous Mode Operation (2A current through motor)
Case 2: Start/Stall Mode Operation (10A current through motor)
EI
√√
V12CV
Case 1: Continuous Mode Operation (2A current through motor)
√
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
BI
CV
EV
TorqueSpeed
Eff
Thermal waste at Bipolar Transistor
Continuous
Stall/Start
BI
BR
BR
1021
1
A
2V
.BICV
BRBR
A2.1BIHighest Voltage
Lowest Voltage
V12CV
V0
(Maximum required current)
%3.861012
2.11220.11012
%8.95212
050.01222.0212
CICVBICVCIVCICV
EffSATCE
Estimate of power wasted at BR
Worst Casing:
PMMotor
External Supply
Solving Problem 1
IN4002
KSH3055
10
Turn On byA2.1
V12
… Design Example 1:
Risk Reduction: Analysis of Idea 2
Pin x
Microprocessor
Problem 2(1.2A Exceeds what Micro-Processor
can provide)
… Step 4.
PMMotor
Pin x
Microprocessor
External Supply
IN4002
V12
… Step 4. Analysis
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
Problem 3More data needed
KSH3055
10
Turn On byA2.1
To protect against excessive current
Sub-Step A. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design
* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408)
- This is an PNP Bipolar Transistor
- Look at downloaded “Bipolar Power Transistor Selection Guide” from
- http://www.fairchildsemi.com/
- Looked in and column under General Purpose Transistors
- Picked “KSH210” with and
Step 3. Downloaded and Reviewed Spec sheet
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.)
- (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408) - Looked at and in the spec sheet of Chips it returned (to select a reasonable gain and current output)FEh
FEh
18045 FEh
A2.1 BIFEhCI
CI
CI
A5CI
V12
BI
Step 4. Analysis to determine - : required current to turn On - : Protective resistor
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
2BI
2BR
A2.1 BIFEhCI
V12
2BI
2BR
To simplify modeling and calculations, losses in this transistor is ignored compared to the other one
Minimizing leakage current when ON: KΩΩA
V11000
012.0
122 BR
KSH210
mAAA
25017.070
2.1
FEhCI
BIBIFEhCI
Overdrive
PMMotor
Pin x
Microprocessor
External Supply
IN4002
V12
… Step 4. Analysis
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
Problem 3The current is small.
However, the circuit on right has high current.Need to protect the microprocessor.
KSH3055
10
Start Motor bymA25
kΩ 1
KSH210
PMMotor
Pin x
Microprocessor
External Supply
IN4002
V12
… Step 4. Analysis
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
KSH3055
10
Start Motor bymA25
kΩ 1
KSH210
Opto Isolator http://www.fairchildsemi.com/ HSR312
kΩ 1 Ω400
Ω)(overdrive
Ω0.025
12V
400
480
Ω0.005
5V1000
Bipolar T Bridge
… Step 4. Analysis
… Design Example 1:
… Risk Reduction: Analysis of Idea 2
PMMotor
Pin x
Microprocessor
External Supply
IN4002
V12
KSH3055
10
kΩ 1
KSH210
kΩ 1 Ω400
Design merits of Idea 2:
Cost= $B
# of Components = 8
WlStart/Stal 120P
WContinuous 24P
%8.95lStart/StalEff
%3.86ContinuousEff
HSR312
Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design
* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408)
… Design Example 1:
Risk Reduction: Analysis of Idea 3
PMMotor
Pin x
Microprocessor External Supply
IN4002
V12
Darlington Transistor
kΩ 1
HSR312
BIFEhCI
3BI
3R
CIBIEI
4R
Assignment: - Determine a Darlington Transistor Part number- Download its spec sheet and determine and for two cases: Continuous and Start/Stall - Follow similar analysis to idea 2 and determine * Determine (Worst Casing) * Determine to have the transistor ON for 2 cases: Continuous and Start/Stall * Determine efficiency for 2 cases: Continuous and Start/Stall * Determine to minimize leakage current when ON
FEh satCEV
3BI3R
Restriction: ONLY one (2-sided) sheet of paper
4R
Make a decision
...%lStart/StalEff
...%ContinuousEff
Design merits of Idea 3:
Cost= $C
# of Components = 5
MOSFET Bipolar T Bridge
Darlington
Build
Trouble Shoot
Optimize
Design merits of Idea 2:
Cost= $B
# of Components = 8
WlStart/Stal 120P
WContinuous 24P
%8.95lStart/StalEff
%3.86ContinuousEff
%7.96lStart/StalEff
%3.99ContinuousEff
Design merits of Idea 1:
Cost= $A
# of Components = 2
WlStart/Stal 120P
WContinuous 24P
WlStart/Stal 120P
WContinuous 24P
… What could happen if no analysis was done?