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Electronic Power and Control. Electronic Power and Control. Semiconductors. Semiconductors. The Elements. Simpler Table of Elements. Silicon. Germanium. Inert Gases. Semiconductors. Poor Conductors. Good Conductors. Semiconductors.

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Electronic Power and Control

Electronic Power and Control

Semiconductors

Semiconductors


The Elements

Simpler Table of Elements

Silicon

Germanium

Inert Gases

Semiconductors

Poor

Conductors

Good

Conductors


Semiconductors

A SEMICONDUCTOR has FOURelectrons in its outermost shell or orbit.

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

Outermost Electrons

form PAIR BONDS


Semiconductors

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

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

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

This is Called “P-TYPE”


Semiconductors

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

The “extra” electron is NEGATIVELY charged.

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

This is Called “N-TYPE”


Junction Diode

If external voltage is applied:

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 PARALLEL CAPACITOR opposes change in VOLTAGE

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

A SERIES INDUCTIVE CHOKE opposes change in CURRENT


Rectifier Filters

Choke Input L/C Filter

The Choke filters changes of current;

the Capacitor gives higher load voltage

A Capacitor and Choke are often used together.


Single-Phase Full-WaveBridge Rectifier

Diode – voltage, current and PIV ratings to suit application

AC Supply - oftenfrom a transformer

(example: 12V 50Hz)

DC Load to be supplied by Rectifier


Single-Phase Full-WaveBridge Rectifier

Conduction During

Positive ½ Cycle


Single-Phase Full-WaveBridge Rectifier

Conduction During

Negative ½ Cycle

Back


Three-Phase Waveforms

3-phase AC Features

2400

1200

Phase Voltages are 1200 out-of-phase


Three-Phase Half-Wave Rectifier

3-phase STAR connectedtransformer secondary

Diode in each “Active”

VAC (RMS)

AC Voltage is PHASE Voltage (Active-Neutral)

Return to transformer “Star Point” (Neutral)



Three-Phase Half-Wave Rectifier

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

Maximum value = VPeak

Minimum value = VPeakx0.5


Three-Phase Full-Wave Rectifier

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

Maximum value = VPeak

Minimum value = VPeakx0.866


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

The Zener Diode voltage appears across the load.

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

8.2V

8.2V 1W

3.8V

12VDC


Voltage Regulator

ZENER SHUNT REGULATOR

Assume the load has a resistance of 200 ohms

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

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

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

97mA

8.2V

41mA

8.2V 1W

3.8V

12VDC


Voltage Regulator

THREE-TERMINAL REGULATOR

(7xxx Series)

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

Output

Input

Input

Ground

Ground

Output


Voltage Regulator

THREE-TERMINAL REGULATOR

(7xxx Series)

Positive Output

7812

7812

Input

Regulated Voltage (12V)

Ground

Output


Voltage Regulator

THREE-TERMINAL REGULATOR

(7xxx Series)

Negative Output

7912

7912

Ground

Regulated Voltage (12V)

Input

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 POSITIVE

relative 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.

This varies the Trigger Point, controlling the average load current

Trigger Point can be delayed ONLY to 900

Animated


Electronic Control Devices (Thyristors)

Silicon Controlled Rectifier (SCR)

Varying R1 varies charging rate of the Capacitor.

This varies the Trigger Point, controlling the average load current

Trigger Point can be delayed up to nearly 1800

Animated


Electronic Control Devices (Thyristors)

Silicon Controlled Rectifier (SCR)

Waveform across Load

Waveform across SCR


Electronic Control Devices (Thyristors)

TRIAC

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

MT2

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

A DIAC is like a TRIAC without a Gate. It conducts in EITHER direction when a voltage across it reaches a required threshold value

MT1

Gate

DIAC


Electronic Control Devices (Thyristors)

TRIAC

Varying R1 varies charging rate of the Capacitor.

This varies the Trigger Point, controlling the average load current

Animated


Electronic Control Devices (Thyristors)

TRIAC

Waveform across Load

Waveform across TRIAC


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