PROTECTION OF SCR

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di/dt Protection:
When a thyristor is forward biased and is turned ON by a gate pulse, conduction of anode current begins. If the rate of rise of anode current (di/dt) is very fast compared with the spreading velocity of charges a local hot spots will be formed. This localised heating may destroy the thyristor. Therefore, the di/dt rate of rise of anode current at the time of turn on must be kept below the specified limiting value by using a small inductor, called di/dt inductor, in series with the anode circuit.
dv/dt Protection:
If the rate of rise of applied voltage across thyristor is high, the device may get turned on. Such phenomena of turning on a thyristor, called dv dt turn on must be avoided as it leads to false operation.
False turn on of an SCR by large- dv dt even with out application of gate signal can be prevented by using a Snubber circuit in parallel with the device.

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