> [...]
> > In my own power supplies, I've usually put a switch on the output, so
that
> I can leave the supply powered up and simply switch the output on and
off.
> But the bench supplies I've bought never seem to have that feature,
which
> has always puzzled me.
>
> Such a switch can get you into trouble, if it applies an instantaneous
> supply-voltage step to a circuit. The dV/dt slew rate can be very high.
Hmm, good point. Of course, that could happen in the as-manufactured circuit too - some of my circuits get powered by batteries, turned on by a switch, so there's going to be as much dV/dt as the internal impedance of the battery permits. If the circuit dies on the power supply, it might be telling me something.
I guess what I really want is a switch that either cuts the output to zero or ramps it back up to the preset voltage over the course of, say, 100msec. I do want it to go all the way to zero, though, so that when I'm fooling around with the circuit I don't inadvertently reverse-bias a tantalum cap or whatever. Alternately, I want the max current to be limited to < 5mA or so - which amounts to the same thing.
It always makes me uncomfortable to turn on a circuit under test by means of turning on the AC to the bench power supply. I wonder whether the supply's current limiting circuitry will be able to kick in in time, whether the voltages will stabilize right away, and so forth. I guess I've never actually had a problem with it, though; not sure why.
-w