Gate triggering method is the most efficient, simple, reliable and common method to turn on a thyristor. A positive gate signal is used to turn-on the thyristor in this method even before the specific breakdown voltage. When the thyristor is forward biased, sufficient positive gate signal is applied between the gate and cathode terminals which injects electrons into the junction j2 resulting increases in reverse leakage current causing breakdown at the junction j2.
The conduction period of thyristor can be controlled by varying the gate current within the minimum and maximum values. There are three types of signal which can be used for gate triggering that are listed below.
- DC signal
- Pulse signal
- AC signal.
DC Gate Triggering Method
In this gate triggering method, sufficient DC voltage is applied between the gate and cathode terminals in such a way that the gate terminal is made positive with respect to the cathode terminal. The dc current flowing through the gate is responsible for the breakdown of the junction j2 and turns-on the thyristor.
In this method, a continuous dc gate signal is applied causing more internal power dissipation and increases power losses.
Pulse Gate Triggering Method
The most popular gate triggering method for triggering a thyristor is the pulse gate triggering method. In this method, the gate terminal is supplied with single pulse or a train of high frequency pulses which turns-on the thyristor.
The main advantages of pulse triggering method is that the gate drive is discontinuous i.e. doesn't supply pulse signal after turning on the thyristor which reduces the power dissipated at the gate i.e. reduces the losses at the gate.
AC Gate Triggering Method
The most commonly used gate triggering method for triggering a thyristor is the AC gate triggering method especially in ac application. In this method, the thyristor is triggered by the phase shift ac voltage derived from the main supply. The firing angle is controlled by changing the phase angle of ac signal.
Only half cycle of the ac signal is available for the gate drive to control the firing angle and for the another half cycle a reverse voltage is applied across the gate and cathode terminal. Here is also the need of a separate step-down transformer to supply the voltage to drive the gate. These are the two limitations of the ac gate triggering method.
Conclusion
Hope, you have clearly understand about the gate triggering method to turn on a thyristor and all three signals used to turn on the thyristor. Make sure to leave your opinion and suggestion about this post in the comment section below.