Gate Turn Off Thyristor

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1.) How gating of a thyristor works?

A thyristor is a 4 layer 3 terminal device with 3 junctions. When the anode terminal has positive voltage and no gate voltage is applied, the first and the third junction are forward biased and the second junction is turned reverse biased allowing no current flow through the thyristor.

A thyristor starts to conduct when the voltage across the anode and cathode (VAK) is increased beyond the thyristors breakdown voltage (VBO). This is due to the avalanche breakdown that occurs in the second junction of the thyristor. When a gate voltage is applied at the gate terminal, the avalanche breakdown in the second junction of the thyristor occurs at lower values of VAK. Thus, thyristors can be switched suddenly by applying the suitable value for the gate voltage. Voltage pulses can be used as gate triggering voltage at the gate terminal.

A thyristor continues to conduct even when the triggering gate voltage is removed. It only stops conducting when the gate voltage is removed and the current across the anode and cathode is less than the holding current.

2.) Gate Turn Off Thyristor

A. Introduction

Gate turn off (GTO) is a type of thyristor that can be turned on and turned off. The turning on and off of the device can be accomplished by applying the correct voltage in the gate terminal. Applying a positive voltage to the gate terminal turns the GTO in on state while applying a negative voltage turns the GTO in off state.

GTO advantages :

➢ High voltage and current capability.

➢ Low cost.

➢ Low conduction loss.

GTO disadvantages :

➢ Non uniform turn on and turn off current.

➢ Long switching time.

➢ No current limitation.

➢ High gating power.

B. Structure And Operation


GTO Symbol And Basic Structure

GTO can be turned off just like other...
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