what is gate turn off thyristor (GTO)?

Question

Draw the structural diagram of GTO. Explain briefly the switching behavior of GTO with the help of appropriate voltage and current waveform.

Answer 1

Gate Turn Off Thyristor (GTO)

• Conventional Thyristor can be turned on with gate terminal but can not turn off from gate terminal.
• But in case of Gate Turn Off Thyristor (GTO), we can turn it on and off from its gate terminal.
• By giving positive signal GTO can be turned on and by giving negative signal it can be turned off.
•GTO is used for the chopper and PWM inverter applications.
•GTO is a three-terminal device.
•Basically, it has four layers PNPN.
• GTO has high voltage blocking capability and high overcurrent capability.
•In on state GTO operate like conventional thyristor.
• GTO turn off occur by removal of excess holes in cathode base region by reversing the current through gate terminal.
•Stopping the current through the gate can turn off GTO.

Switching behavior of GTO :

The figure shows the basic gate drive circuit for GTO. GTO required positive gate pulse to turn on, this positive gate pulse is applied using the gate drive circuit. The transistor TR! is turn on which turn on the transistor TR2 and TR2 provide the positive gate pulse to GTO. The thyristor can be turned off by the negative gate pulse, this negative gate pulse is supplied by gating thyristor T1, which provides the negative gate pulse to GTO and turned it off. Higher the forward gate current smaller the turning on time. When the anode current is more than latching current we may remove the gate drive. The figure shows the switching characteristics of GTO. In switching characteristics of GTO the T_q is the total turn off time. T_q is subdivided as storage period (Ts), fall period (T_p) and tail period (T_t).