SILICON CONTROLLED RECTIFIER

(SCR/THYRISTOR)

SCR CONSTRUCTION

SCR EQUIVALENT CIRCUIT

SCR WORKING ( Case 1: Gate open )

SCR WORKING ( CASE 2: Gate Negative w.r.t Cathode )

•When a negative gate – cathode voltage (-VG) is applied, the T2 base-

emitter junction is reversed & only small leakage continue to flow, so both T1 and T2 remain off

SCR WORKING ( CASE 3: Gate Positive w.r.t Cathode )

SCR REVERSE CHARACTERISTICS

SCR FORWARD CHARACTERISTICS

SCR CHARACTERISTICS

GENERAL METHODS FOR TURNING OFF SCR

1. Reduce the VAK to Zero

2. ANODE CURRENT INTERRUPTION

3. FORCED COMMUTATION TECHNIQUE

GENERAL METHODS FOR TURNING OFF SCR

FORCED COMMUTATION TECHNIQUE

APPLICATIONS OF SCR•SPEED CONTROL OF DC MOTORS

•AS RECTIFIER FOR CONVERSION AC TO DC

•BATTERY CHARGING REGULATOR

•PHASE CONTROL

•OVER VOLTAGE PROTECTION CIRCUIT

•EMERGENCY LIGHTING SYSTEM

•HEAT CONTROL CIRCUIT

GATE TURN OFF DEVICE (GTO)

REFERENCE

•ELECTRONIC DEVICES & CIRCUITS BY DAVID A BELL