Gate Turn On Turn Off Thyristors

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What is a thyristor?

Thyristors are power semiconductor devices used in power electronic circuits

They are operated as bistable switches operating from non-conducting to conducting states.

They are made of 4 layers and 3 pn junctions.

Thyristors are three terminal devices the terminals being anode, cathode and gate.


Working of a thyristor


When anode voltage is positive with respect to cathode junctions J1 and J3 are forward biased and junction J2 is reverse biased and the thyristor is off. This state is called forward blocking state.

When the voltage is increased the reverse junction breaks and it is called forward breakdown voltage.

In this state a large anode current flows and the thyristor is said to be on or in conducting state


CONSTRUCTION OF GTO


Compared to a conventional thyristor it has an additional n+ layer near the anode .

In order to obtain high emitter efficiency the n+  cathode layer is highly doped.

This forms the turn off circuit between the gate and the cathode.

The doping level of the p type gate region is highly varied.