Electrical – diode selection for large current reverse bias, small current forward bias

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I'm designing a circuit where I want to pass a small test current from one leg, but block a large "firing" current (rocketry) coming from another leg in reverse bias. I have a 5vdc indicator line (with about 1-2 vdc and <.5 amp once it would get to the diode) I want to pass through a forward biased diode to indicate the fuse is still viable without burning the fuse, but need that same diode needs to block 12 vdc at as much as 30 amps in reverse bias for a short duration (maybe as long as 5 second until the igniter lets go and opens the circuit and the "firing" voltage is turned off manually). How do I select the proper diode? What am I looking for on the diode spec sheet to be sensitive enough to allow the low current forward bias and strong enough to block the large current reverse bias. I know that is what diodes do, but how to select the right one escapes me.enter image description here

Best Answer

What am I looking for on the diode spec sheet to be sensitive enough to allow the low current forward bias and strong enough to block the large current reverse bias. I know that is what diodes do, but how to select the right one escapes me.

Just use a high speed diode like a 1N4148, BAS16 or 1N914. It will certainly block 12 volts and won't conduct any appreciable reverse current when the heavy duty 12 volt supply is activated. I said use a fast diode because reverse recovery time for those stated above and in the single figure nano second range.