Numerical - Input voltage required for the breakdown in SCR

Determine the input voltage necessary to cause the breakdown in SCR for 200 Ω resistance connected in series if the required gate current for firing is 6 mA.


a. 2.7 V
b. 2.9 V
c. 1.9 V
d. 1.2 V

Correct Answer: c. 1.9 V


In accordance to the given data and the reference diagram, it is mandatory to estimate the value of input voltage in such a manner that it should overcome the barrier voltage of 0.7 V.

Secondly, it should allow the current of 6 mA to flow through the resistor of about 200 Ω.

Hence, from the figure, the value of input voltage can be estimated as,

Input Voltage = Gate to Cathode Voltage + (Gate Current x Resistance)

Thus, Vin = VGC + IG R
= 0.7 +( 6 x 10-3 x 200 )
= 0.7 + (1200 x 10-3 )
= 1.9 V
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