I spend too much of my life worrying about current limiters.
This time, I have a 5 volt power supply, powering some logic that drives a customer load. The load should be 50 ohms, but someone might decide to short it, and I don't want to fry the driver or drag down the +5 rail. So I need a low dropout (under 0.1 volts maybe) roughly
120 mA current limiter. I need two, actually, for two output drivers, and I don't have much room or budget.I can't find any commercial limiter chips or LDOs that can do this. The limiters mostly work at USB levels, 1 amp roughly, and the LDOs have wild short-circuit current spans, like 3:1 or something.
Looks like I'll have to do it myself. This isn't bad:
It's a limiter, not a regulator, so the loop doesn't need to be stable. I think.
(I think I need some new whiteboard markers, too.)