Electronic Power and Control

Semiconductors

Electronic Power and Control

Semiconductors

The ElementsSimpler Table of Elements

GoodConductors

PoorConductors In

ert G

ases

Sem

icon

duct

ors

Silicon

Germanium

Semiconductors

A SEMICONDUCTOR has FOURelectrons in its outermost shell or orbit.

Outermost Electronsform PAIR BONDS

Adjacent atoms SHARE Electron Pair Bonds; the crystal structure behaves like an INSULATOR

If the semiconductor has a few per million atomswith THREE outermost (valence) electrons ....

... THREE valence atoms leave a “HOLE” in the crystal structure.

The “Hole” is an absence of an electron, and is thus POSITIVELY charged.

Semiconductors

This is Called “P-TYPE”

If the semiconductor has a few per million atomswith FIVE outermost (valence) electrons ....

... FIVE valence atoms have an “extra” electron in the crystal structure.

The “extra” electron is NEGATIVELY charged.

Semiconductors

This is Called “N-TYPE”

If external voltage is applied:

Junction Diode

NEGATIVE to ANODE; POSITIVE to Cathode

The Depletion (Barrier) Zone is increased,BLOCKING CONDUCTION

Rectifier Filters

The parallel load also draws current from supply during the charging period .....

.... and also during discharge.

.... the resulting Ripple depends on the load resistance AND capacitor size.

Rectifier Filters

No Load (load open circuit) ....

Capacitor charges and holds peak value.

Rectifier Filters

Moderate Load ....

Capacitor charges to Peak value as voltage rises,but discharges when voltage drops away.

Rectifier Filters

Heavy Load ....

Capacitor charges to Peak value as voltage rises,but discharges greatly when voltage drops away.

Rectifier Filters

Series Choke Filter

A SERIES INDUCTIVE CHOKE opposes change in CURRENT

A PARALLEL CAPACITOR opposes change in VOLTAGE

However, being SERIES, there will be some voltage dropacross the resistance of the choke

Rectifier Filters

Choke Input L/C Filter

A Capacitor and Choke are often used together.The Choke filters changes of current;the Capacitor gives higher load voltage

Single-Phase Full-WaveBridge Rectifier

AC Supply - oftenfrom a transformer(example: 12V 50Hz)

Diode – voltage, current and PIV ratings to suit application

DC Load to be supplied by Rectifier

Single-Phase Full-WaveBridge Rectifier

Conduction DuringPositive ½ Cycle

Single-Phase Full-WaveBridge Rectifier

Back

Conduction DuringNegative ½ Cycle

Three-Phase Waveforms3-phase AC Features

Phase Voltages are 1200 out-of-phase

1200

2400

Three-Phase Half-Wave Rectifier

3-phase STAR connectedtransformer secondary Diode in each “Active”

Return to transformer “Star Point” (Neutral)

AC Voltage is PHASE Voltage (Active-Neutral)

VAC (RMS)

Three-Phase Half-Wave Rectifier

(Animated)

Three-Phase Half-Wave Rectifier

Maximum value = VPeak Minimum value = VPeakx0.5

VRipple = VPeak – (VPeak x 0.5) = VPeak x 0.5

Three-Phase Full-Wave Rectifier

Maximum value = VPeak Minimum value = VPeakx0.866

VRipple = VPeak – (VPeak x 0.866) = VPeak x 0.134

Voltage Regulator

ZENER SHUNT REGULATOR

Assume the filtered rectifier output is 12 volts DCand the Zener Diode is rated at 8.2 volts, 1 watt

Excess voltage (12 – 8.2 = 3.8V) isdropped across the SERIES RESISTANCE (RS)

The Zener Diode voltage appears across the load.

8.2V3.8V12VDC

8.2V 1W

Voltage Regulator

ZENER SHUNT REGULATOR

Assume the load has a resistance of 200 ohms

Power rating of RS = 3.8 volts x 0.097 amps= 0.37 watts MINIMUM

Load current = 8.2 volts ÷ 200 ohms = 0.041 amps = 41mA

8.2V3.8V12VDC

8.2V 1W

97mA

41mA

Zener Current = IRS – ILoad = 97mA – 41mA = 56mA

Voltage Regulator

THREE-TERMINAL REGULATOR(7xxx Series)

The 3-Terminal Regular is an integrated circuit chip with INPUT, OUTPUT and GROUND or COMMON terminals

Input

Input

Output

Output

Ground

Ground

Voltage Regulator

THREE-TERMINAL REGULATOR(7xxx Series)

7812

Input

Output

Ground

Positive Output

7812

Regulated Voltage (12V)

Voltage Regulator

THREE-TERMINAL REGULATOR(7xxx Series)

7912

Input

OutputGro

und

7912

Regulated Voltage (12V)

Negative Output

Voltage Regulator

THREE-TERMINAL REGULATOR(Typical Connections)

In operation, a small QUIESCENT CURRENT (IQ)flows between INPUT and GROUND

IQ = 2mA to 5mA

Electronic Control Devices (Thyristors)

Thyristors are solid-state devices used to control power to a load

Silicon Controlled Rectifier (SCR)

The DIODE conducts when the Anode is POSITIVE relative to the Cathode.

The SCR conducts when the Anode is POSITIVE relative to the Cathode, PLUS ....

..... the GATE must be POSITIVErelative to the Cathode

Electronic Control Devices (Thyristors)

Silicon Controlled Rectifier (SCR)

Once the SCR is conducting, the GATE loses ALL CONTROL

The SCR can only be turned OFF by removing the Anode-Cathode voltage

Electronic Control Devices (Thyristors)

Silicon Controlled Rectifier (SCR)

Varying R1 varies the voltage available at the Gate at any instant.

Animated

This varies the Trigger Point, controlling the average load current

Trigger Point can be delayed ONLY to 900

Electronic Control Devices (Thyristors)

Silicon Controlled Rectifier (SCR)

Varying R1 varies charging rate of the Capacitor.

Animated

This varies the Trigger Point, controlling the average load current

Trigger Point can be delayed up to nearly 1800

Electronic Control Devices (Thyristors)Silicon Controlled Rectifier (SCR)

Waveform across Load Waveform across SCR

Electronic Control Devices (Thyristors)

TRIAC

To provide a short trigger pulse, a DIAC is often used with an R/C network

Like the SCR, The TRIAC is used to control loads, but with current in EITHER direction

MT2

MT1Gate

A DIAC is like a TRIAC without a Gate. It conducts in EITHER direction when a voltage

across it reaches a required threshold value

DIAC

Electronic Control Devices (Thyristors)

TRIAC

Varying R1 varies charging rate of the Capacitor.

Animated

This varies the Trigger Point, controlling the average load current

Electronic Control Devices (Thyristors)TRIAC

Waveform across Load Waveform across TRIAC