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Questions and Answers
What is the main difference between an SCR and an SUS?
What is the main difference between an SCR and an SUS?
What is the primary method of turning on an SCR?
What is the primary method of turning on an SCR?
What is the main advantage of using an SCR over a mechanical switch?
What is the main advantage of using an SCR over a mechanical switch?
What is the purpose of reducing the anode current to the holding current?
What is the purpose of reducing the anode current to the holding current?
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What is the purpose of forced commutation?
What is the purpose of forced commutation?
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What is the significance of the Holding Current (IH) in SCR characteristics?
What is the significance of the Holding Current (IH) in SCR characteristics?
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What is the purpose of the Gate Trigger Voltage (VGT)?
What is the purpose of the Gate Trigger Voltage (VGT)?
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What is the Peak Reverse Voltage (PRV) in SCR characteristics?
What is the Peak Reverse Voltage (PRV) in SCR characteristics?
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Study Notes
SCR Basics
- SCR is a four-layer PNPN device with three terminals: anode, cathode, and gate.
- Similar to a four-layer diode, but with three terminals.
SCR Normal Operation
- Supply voltage is generally less than breakover voltage value at IG=0.
- SCR is turned on by passing an appropriate amount of gate current (a few mA).
- SCR must not exceed the reverse breakdown voltage when operated from an AC supply.
- To turn off an SCR, anode current should be reduced to holding current.
- Increasing gate current above the required value can cause the SCR to close at a much reduced supply voltage.
SCR as a Switch
- Advantages over mechanical or electromechanical switches:
- No moving parts, resulting in noiseless operation at high efficiency.
- High switching speed, up to 10^9 operations per second.
- Control over large current (30-100 A) in the load by means of a small gate current (a few mA).
- Small size and trouble-free service.
Turning off an SCR
- Anode current interruption: suppressing anode current from going through the anode to the cathode terminal.
- Methods: series switch and parallel switch.
- Forced commutation: momentarily forcing current through the SCR in the opposite direction to reduce net forward current below holding value.
SCR Characteristics and Ratings
- Forward Breakover Voltage (VBR(F)): voltage at which SCR enters forward-conduction region.
- Holding Current (IH): anode current value below which SCR switches from forward-conducting to forward-blocking region.
- Gate Trigger Current (IGT): gate current value necessary to switch SCR from forward-blocking to forward-conducting region.
- Gate Trigger Voltage (VGT): voltage across gate-cathode junction that turns SCR on.
- Average Forward Current (IF(AVG)): maximum continuous anode current SCR can withstand in forward-conducting region.
- Peak Reverse Voltage (PRV): maximum reverse voltage that can be applied to an SCR without conducting in a reverse direction.
- Circuit Fusing Rating: product of square of forward surge current and time of duration of the surge.
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Description
This quiz covers the normal operation of Silicon Controlled Rectifiers (SCRs), including supply voltage, gate current, and peak reverse voltage. Learn about the characteristics of SCRs in normal operation.
