Question

An SCR has a breakover voltage of 450 V, a trigger current of 20 mA and holding current of 20 mA. What do you understand from it? What will happen if gate current is made 40 mA?

Answer 1

1. When breakdown voltage is 450V - It means that if the gate terminal is open and the supply voltage is 450 V, then SCR will start conducting heavily. However, as long as the supply voltage is less than 450 V, the SCR stays open i.e. it does not conduct.

2. When trigger current is of 20mA - It means that if the supply voltage is less than breakover voltage (i.e. 450 V) and a minimum gate current of 20 mA is passed, the SCR will close i.e. starts conducting heavily. The SCR will not conduct if the gate current is less than 20 mA. It can be said that triggering is the normal way to close an SCR as the supply voltage is normally much less than the breakover voltage.

3. When holding current is of 20mA - When the SCR is conducting, it will not open (i.e. stop conducting) even if triggering current will be removed. However, if the supply voltage is reduced, the anode current also decreases. When the anode current drops to 20 mA, the holding current, the SCR is turned off.

If the gate current is made 40 mA, then the SCR will be turned on the lower supply voltage.