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Wednesday, October 5, 2011

SILICON-CONTROLLED RECTIFIER(SCR) CHARACTERISTICS Electronic devices and circuits lab manual

AIM:  To draw the V-I Charateristics of SCR
                           Regulated Power Supply (0-30V)
                           Resistors 10kΩ, 1kΩ
                           Ammeter (0-50) µA
                           Voltmeter (0-10V)
                           Connecting Wires.


It is a four layer semiconductor device being alternate of  P-type and N-type silicon. It consists os 3 junctions J1, J2, J3 the J1 and J3 operate in forward direction and J2 operates in reverse direction and three terminals called anode A, cathode K , and a gate G. The operation of SCR can be studied when the gate is open and when the gate is positive with respect to cathode.
                When gate is open, no voltage is applied at the gate due to reverse bias of the junction J2 no current flows through R2 and hence SCR is at cutt off. When anode voltage is increased J2 tends to breakdown.
                 When the gate positive,with respect to cathode J3 junction is forward biased and J2 is reverse biased .Electrons from N-type material move across junction J3 towards gate while holes from P-type material moves across junction J3 towards cathode. So gate current starts flowing ,anode current increaase is in extremely small current junction J2 break down and SCR conducts heavily.
                When gate is open thee breakover voltage is determined on the minimum forward voltage at which SCR conducts heavily.Now most of the supply voltage appears across the load resistance.The holfing current is the  maximum anode current gate being open , when break over occurs.

1.    Connections are made as per circuit diagram.
2.    Keep the gate supply voltage at some constant value
3.    Vary the anode to cathode supply voltage and note down the readings of voltmeter and ammeter.Keep the gate voltage at standard value.
4.    A graph is drawn between VAK and IAK .
IAK ( µA)

RESULT:    SCR Characteristics are observed.


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