Now, as the thyristor current is zero it can be considered as an open switch.Also when the supply is closed to the circuit( in the above figure say the switch S is closed), sudden voltage appears across SCR.This causes a voltage spike with the value of L(di/dt). When it reaches a peak value it cannot be further supported by the charge carriers and falls very quickly to zero.Due to the inductance, current continuous to flow due to sweeping of charge carries at the external junctions.When a reverse voltage is applied, commutation process is initiated and the forward current flow through SCR approaches zero.This type of snubber circuit consists of a series combination of resistance R and Capacitance C in parallel with a SCR. RC Snubber Circuit for SCR dv/dt Protection: With the help of snubber circuit, the false turn-on of a thyristor due to large dv/dt can be prevented. The Snubber circuit is one type of dv/dt protection circuit of the thyristor.
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