THYRISTOR Turn OFF Method

The process of turning off a thyristor is called Commutation. When thyristor starts conducting Gate loses control over the device, therefore external method applied to turn off the thyristor.

   1) Anode Current falls below the Holding Current.

  2) Reverse voltage is applied to thyristor for a sufficient time to enable it to recover the blocking state.

Classification of Commutation:-

   1) Class A commutation (Load commutation)

   2) Class B commutation (Resonant Pulse commutation)

   3) Class C commutation (Complementary commutation)

   4) Class D commutation (Impulse commutation)

   5) Class E commutation (External Pulse commutation)

   6) Class F commutation (Line commutation)

Another Classification of Commutation:-

   1) Load commutation (Class A)

   2) Line commutation (Class F)

   3) External Pulse commutation (Class E)

   4) Forced commutation (Class B,C, & D)

THYRISTOR Protection:-

   1) FUSE is used for high current protection.

   2) CAPACITOR is used for dv/dt protection.

   3) INDUCTOR is used for di/dt protection.

   4) Metal Oxide Variester (MOV) is used for high voltage protection.

Application:-

   1) In Controlled Rectifier.

   2) In High power controlled switches.

Advantage:-

   1) High power handling capabilities.

Device Codes:-