An ideal transistor may be turned off; that is its resistance to forwarrd current restored to infinity

while foriward Current is flowing simply by reducing the base Current to zero

This is not tho case witha thyristor. Onceturned on

a thysristor Cn not recover its resista《ne to fovward Current》 nless that Currnt is reduced to zero and held there for at lest the turn-off time. A number of different methods may be employed to Commutte or turn off a thyristor

and the method employed in a partiCulr cse depends on the funetion of the system embodying the thyristor. In this article

the three basic techniques of commuttion are discussed:1

line commutation 2

Lod commutation 3

Forced commutation and illustrated by means of calculation of some simple Circuits.