Is It Possible To Choose a Higher Holding Current When Designing SCR?

Question

I'm looking at this data sheet: SCR data sheet on Digikey

This device seems perfect for what I want to do, with 1 exception:

The holding current is way too low.

Various forums have suggested that (on state current) = k * (holding current), where k is typically between 2 and 3. The factor of 2-3 seems absurdly low compared to the devices I have looked at. For instance, if you search for SCR on Digikey, the highest holding current is a small number of Amps (I see 2) while the on state current goes into the thousands.

What I really want is the holding current to be about 20% of the on state current.

Is there any way to modify the design of the SCR itself to achieve this? (As opposed to using an external transistor to shunt current around the SCR. I'm trying to eliminate external components.)

Answer 1

You can pore over the datasheets and find one that suits you better. Holding current is generally correlated with gate trigger current. Usually you want relatively low current, but not so low you have trouble commutating the thyristor or you get false triggering.

You can add a resistor from gate to cathode, but of course the results are not guaranteed (or even characterized) and may be variable from unit-to-unit. I suspect the ones you're looking at already have a "shorted gate" construction (basically a low-value internal resistance to decrease susceptibility to false (eg. dv/dt) triggering so the external resistor may not have much effect. They are already quite insensitive.

For a sensitive-gate thyristor such as the ancient C106 (~200uA trigger), the resistor can have a large effect:

Image from 1972 GE SCR Manual.