Difference between GTO and SCR

The main difference between a GTO and an SCR is that a GTO can be turned OFF by the application of gate signal whereas SCR can cannot be switched OFF by gate signal. To turn OFF an SCR, a separate commutation circuit is required whereas a Gate Turn Off thyristor can be made OFF by applying negative gate signal at its gate cathode terminal.

Separate commutation circuit is not required for GTO as is the case with an SCR. This makes a GTO superior over an SCR.

Some of the major differences between GTO and SCR is tabulated below. This table can be considered as comparison chart.

Gate Turn Off Thyristor (GTO) Silicon Controlled Rectifier (SCR)
GTO is a four-layer, three terminal pn pn device. The anode is made up of n+ fingers diffused into p+ layer. SCR is also a four-layer, three terminal pn pn device. However, the anode is only made up of p+ layer. This is the basic structural difference between the two.
It is represented by the either circuit symbol (i) or (ii) shown below.


The circuit symbol of SCR is shown below.

circuit Symbol-of-SCR

Commutation circuit is not required and hence, it can be used beyond 1 kHz application. Requirement of bulky and costlier commutation circuit limits its use up to about 1 kHz.
The V-I characteristics is similar to that of an SCR. But the value of latching current is much more (of the order of 2 A). The value of latching current is comparatively less (of the order of 100-500 mA).
The reverse voltage blocking capability is less as compared to SCR. It is typically 20 to 30 V. Reverse voltage blocking capability is comparatively more.
Turn off time comprises of storage time, fall time and tail time. Turn of time can be divided into reverse recovery time and gate recovery time.
Due to multilayer structure, the value of gate triggering current is higher. Gate triggering current is comparatively lower.
Due to elimination of commutation circuit, the commutation losses are eliminated and hence, the efficiency of GTO circuit is more. Efficiency is comparatively low.

Apart from the above tabulated differences, the on stage voltage drop and associated losses are more in GTO. Its gate drive losses are also on higher side as compared to SCR. However, GTO has faster switching speed and more di/dt rating at turn on.

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