Download - Electronic Power and Control
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Electronic Power and Control
Semiconductors
Electronic Power and Control
Semiconductors
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The ElementsSimpler Table of Elements
GoodConductors
PoorConductors In
ert G
ases
Sem
icon
duct
ors
Silicon
Germanium
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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
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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”
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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”
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If external voltage is applied:
Junction Diode
NEGATIVE to ANODE; POSITIVE to Cathode
The Depletion (Barrier) Zone is increased,BLOCKING CONDUCTION
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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.
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Rectifier Filters
No Load (load open circuit) ....
Capacitor charges and holds peak value.
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Rectifier Filters
Moderate Load ....
Capacitor charges to Peak value as voltage rises,but discharges when voltage drops away.
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Rectifier Filters
Heavy Load ....
Capacitor charges to Peak value as voltage rises,but discharges greatly when voltage drops away.
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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
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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
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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
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Single-Phase Full-WaveBridge Rectifier
Conduction DuringPositive ½ Cycle
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Single-Phase Full-WaveBridge Rectifier
Back
Conduction DuringNegative ½ Cycle
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Three-Phase Waveforms3-phase AC Features
Phase Voltages are 1200 out-of-phase
1200
2400
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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)
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Three-Phase Half-Wave Rectifier
(Animated)
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Three-Phase Half-Wave Rectifier
Maximum value = VPeak Minimum value = VPeakx0.5
VRipple = VPeak – (VPeak x 0.5) = VPeak x 0.5
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Three-Phase Full-Wave Rectifier
Maximum value = VPeak Minimum value = VPeakx0.866
VRipple = VPeak – (VPeak x 0.866) = VPeak x 0.134
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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
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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
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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
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Voltage Regulator
THREE-TERMINAL REGULATOR(7xxx Series)
7812
Input
Output
Ground
Positive Output
7812
Regulated Voltage (12V)
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Voltage Regulator
THREE-TERMINAL REGULATOR(7xxx Series)
7912
Input
OutputGro
und
7912
Regulated Voltage (12V)
Negative Output
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Voltage Regulator
THREE-TERMINAL REGULATOR(Typical Connections)
In operation, a small QUIESCENT CURRENT (IQ)flows between INPUT and GROUND
IQ = 2mA to 5mA
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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
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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
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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
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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
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Electronic Control Devices (Thyristors)Silicon Controlled Rectifier (SCR)
Waveform across Load Waveform across SCR
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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
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Electronic Control Devices (Thyristors)
TRIAC
Varying R1 varies charging rate of the Capacitor.
Animated
This varies the Trigger Point, controlling the average load current
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Electronic Control Devices (Thyristors)TRIAC
Waveform across Load Waveform across TRIAC