Gate Turn Off Thyristors

Gate turn off thyristors are high-power semiconductors which are also fully controllable switches capable of being turned on and off by their third lead. This lead is known as the ‘gate’ lead and is what sets a gate turn off thyristor apart from other kinds. Unlike a normal thyristor which is a silicon-controlled rectifier, a gate turn off thyristor can be turned on by a gate signal and turns off by a gate signal of negative polarity. The gate cathode behaves like a PN junction.

The state of ‘turn on’ is achieved by a pulse of positive current between the cathode and gate terminals – with some relatively small voltage. The state of ‘turn off’ is due to a negative voltage pulse between gate and cathode terminals.  About a fifth of the forward current goes into inducing a cathode-gate voltage capable of inducing the forward current to fall, in turn causing the thyristor to go into an ‘off’ state. This is also known as the transition to the ‘blocking’ state.

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