Explain the thermal triggering method of SCR. Enlist different triggering methods of SCR.

Explain the thermal triggering method of SCR. Enlist different triggering methods of SCR.
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1 Answer

Answer :

Types of Triggering:

1) Forward voltage triggering

2) Thermal triggering (Temperature triggering)

3) Radiation triggering (Light triggering)

4) dv/dt triggering

5) Gate triggering

(i) D.C. Gate triggering

(ii) A.C. Gate triggering

(iii) Pulse Gate triggering

Thermal Triggering : 

* If the temperature of a thyristor increases, there is an increase in the number of electron hole pairs. This will increase the leakage current. Therefore the value of α1 and α2 will increase. If (α1 + α2 ) tends to unity, then the thyristor may be turned on. 

* This is called as thermal triggering of thyristor. It is an undesirable feature. The break over voltage goes on decreasing with increase in temperature. 

* In short, due to increase in temperature the thermally generated leakage current increases. This current gets multiplied internally and thyristor is turned on. 
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