Methods of Triggering of Thyristor
The method by which a thyristor is turned on is called triggering of Thyristor. In this process the thyristor brings in conducting state from non-conducting state. A thyristor can be turned on by any one of following techniques. In this article, we will discuss about different methods of triggering of thyristor or SCR.
- Forward voltage triggering
- Gate triggering
- Thermal triggering
- dv/dt triggering
- Light triggering
- Forward Voltage Triggering
When a thyristor is forward biased and the forward voltage applied across the anode and cathode, the width of the depletion layer, starts decreasing. At a breakover voltage the depletion layer vanishes and thyristor starts conducts. The triggering of the device is caused by the cathode, that is why it is called forward voltage triggering methods.
- Gate Triggering
In this method of triggering, source (say battery) connected across gate terminal and cathode. This junction makes forward biased with respect to cathode. Small gate signal applied to a thyristor turned on it. Gate triggering is most common method of triggering. The firing angle of device can be controlled by varying the gate signal.
The Gate triggering methods can be classified as.
- DC gate triggering
- AC gate triggering
- Pulse Gate triggering or UJT triggering
AC triggering may be Resistance r triggering or resistance capacitance rc triggering of scr or thyristor.
Why gate triggering is preferred?
In gate triggering, we can control the output of an SCR or thyristor by gate signal which is applied to the junction J2 that helps to make junction J2 forward biased and small gate signal can be triggered the SCR or Thyristor that is why gate triggering is preferred.
- Thermal Triggering
In this method, heat energy is applied to the thyristor to trigger it. We known semiconductor materials have negative temperature coefficient of resistance. As the external heat energy is applied to thyristor the resistance of the device is caused by using heat, hence the name is thermal triggering method.
- dv/dt Triggering
In this method, the triggering of thyristor is caused by using high rate of rise of voltage is called dv/dt triggering.
- Light Triggering
In this method, light energy fall on the thyristor, which results in electron hole pairs are generated in the device. This increase the flow of current with in the device which in turn causes triggering light activated silicon controlled switch are the examples of used light triggering method.