Explain triggering of SCR using opto-coupler. State its advantages.

Explain triggering of SCR using opto-coupler. State its advantages. 
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1 Answer

Answer :

Triggering of SCR using opto-coupler: 

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A simple opto-coupler based triggering circuit for SCR is shown in the figure. An optocoupler or opto-isolator is a combination of light source and light-sensitive device enclosed in a compartment. The light source is LED or infra-red LED (IRLED) and light-sensitive device may be photo-diode or photo-transistor. Referring to the circuit diagram, when the SCR is to be turned-on, a voltage is applied to base of Q1 through R1. The base current flows and Q1 is turned on. The collector current flow and voltage appears across the LED of opto-coupler. The light emitted by LED falls on the photo-transistor and it is turned-on. When photo-transistor is turned-on. It carries the current, which flows through R3 and acts as gate current for the SCR. Thus gate current is provided to SCR and it is ultimately turnedon. The firing circuit is electrically isolated from SCR circuit but optically coupled. 


Advantages of Opto-Couplers

i)Triggering circuits are well protected due to electrical isolation.

ii)It is small size and light weight device.

iii)Interfacing with logic circuits is easily possible.


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