# Confusion in minimum gate triggering current of SCR

I was reading an article about working and properties of SCR from eleccircuit.com and in a section How to pick a SCR -it is written that we should check its rating and one of the mentioned rating in this article is - IGTmin rating (Minimum gate triggering current) i.e the minimum gate current that can trigger the SCR.

But isn't minimum gate current rating should be zero because at breakdown forward voltage we need no gate current at all for forward conducting mode?

And how this minimum gate current (IGTmin) rating is calculated, what is its significance?

• It is not calculated, it's measured. Apr 3, 2021 at 17:29
• What do you mean by "breakdown forward voltage"? Apr 3, 2021 at 17:43
• @Transistor error, it should be VBO (Forward breakover voltage) is the voltage causes SCR to start conducting without no gate current. Or, The maximum voltage that SCR can tolerate. Apr 3, 2021 at 17:48
• We (generally) don't use them in forward breakover voltage as there is no control. We keep below that voltage so that we can control the SCR using the gate. Apr 3, 2021 at 17:51
• @Transistor ok, but let's say I want to to measure minimum Gate triggering current of SCR , for that I have to know what minimum voltage or current ,we have to apply across SCR and finally we can conclude what should be its IGT rating but there is no mention of minimum voltage or current , so what is the prodecure of IGT measurement? Apr 3, 2021 at 18:22

The minimum gate triggering current is the smallest current you need to give the SCR to guarantee triggering under normal working conditions.

This is the amount of current the rest of your circuit needs to provide. If your circuitry provided less than this the operation could fail to function properly under some conditions. For example high-temperature, low temperature or with a device that is not as sensitive but still meets the datasheet specification.

This current requirement is not calculated as such. The device will be designed to meet a specific minimum gate triggering current. Every device will be tested when manufactured but only under a specific set of conditions. As a circuit designer you will need to calculate the minimum gate current your driver circuit will provide and ensure it meets the minimum requirement of the SCR.

The minimum trigger current is not very dependent upon the voltage between the anode and cathode until the breakdown voltage is reached, however it may be significantly dependent upon the device temperature with much more current being required at low temperatures.

For example see figures 3 and 5: C106 SCR datasheet

• Hi Kevin , isn't forward break over voltage is also an rated voltage and should be considered as working normal condition and hence minimum gate triggering Current should be Zero? Apr 3, 2021 at 17:50
• @user215805 - that's an abnormal condition. You would normally design a circuit so that forward breakdown never occurred. Zero would not be a useful figure to put on the data sheet, the circuit designer needs to know how much current is required to trigger the SCR all the other conditions to ensure it is met. Apr 3, 2021 at 18:55
• Ok, I'm accepting your answer ,in data sheet you linked , why voltage across anode to cathode is taken as 4V for minimum and maximum gate trigger Current ,on what basis 4V is chosen not any other voltage ? Apr 3, 2021 at 19:36
• @user215805 - where did it say 4V? In the table it states 6V as Vak. That is somewhat arbitrary, the gate trigger current is not significantly dependent on Vak. It is easier to test at low voltages and currents. Apr 3, 2021 at 20:52