Gate Turn-Off Thyristor(GTO)

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What is GTO?

GTO
GTO is a three terminal device with anode, cathode and gate. It is similar to SCR. The major difference between SCR and GTO is that GTO can be turned off. GTO is a PNPN device that can be turned on by applying positive gate pulse and turned off  by applying negative gate pulse. So, it is called as non-latching device. It has higher switching speed than SCR and it can withstand higher voltage and current. At present, GTO with ratings up to 5000 V and 3000 A are present. 
GTO symbol

The GTO switches regeneratively into the on-state when a positive gate signal is applied to base of NPN transistor. During turn-off, the internal regeneration is reduced by reducing the current gain of the PNP transistor which draws sufficient current from the gate.
GTO transistor model

The reduction in gain of NPN transistor can be achieved by,
  • Gold doped GTO
  • Anode-shorted GTO
 Gold doped GTO                       Anode-shorted GTO                   
 More on-state voltage drop Low on-state voltage drop
 High reverse-voltage blocking capability Low reverse-voltage blocking capability  
 Suitable for high frequency operation Suitable for low frequency operation

How GTO is turned-off?

When a negative pulse is applied to the gate, excess carriers are drawn from the base region of the NPN transistor and collector current of PNP transistor is diverted into external gate circuit. Thus, the base drive of NPN transistor is removed and this, in turn, removes the base drive of PNP transistor and stops conduction. 

Switching Performance

The energy required to turn-off GTO is much less than conventional thyristor. The switching performance can be classified as,
  • Gate turn-on mechanism
  • Gate turn-off mechanism
Gate turn-on mechanism
GTO gate turn on
Gate turn-off mechanism
GTO gate turn-off
Applications
  • Robotics
  • Traction
  • Adjustable inverter drives
  • Rolling mills
References

1] M.D. Singh and K.B. Khanchandani, "Power Electronics", Mc Graw Hill India, 2013.
2] Rashid M.H., "Power Electronics Circuits, devices and Applications", Prentice Hall, India, Third            Edition, New Delhi, 2004.
3] P.S.Bimbra, "Power Electronics", Khanna Publishers, Eleventh Edition, 2003.

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