Re: Space Duel Power Supply -- Part II

"Christopher X. Candreva" wrote:

> On Fri, 15 Oct 1999, Mitchell Rohde wrote:
>
> > I'm not looking at the supply schematic, but a diode on the output of a
> > regulation circuit is intended to protect it from back-spikes ....
> > quick changes in load/inductances can create harmful spikes that can
> > damage regulators. Does the diode go between the output and a
> > cap/ground...?
>
> There's a 1uf electrolytic in parallel with the diode, both from +15 to
> ground. I guess what's confusing me is I'm used to seeing clamping diodes
> directly on high back EMF devices -- motors, coils, even chips, not at
> the supply itself.
>

Then it must be there to keep the output from getting driven
negative, probably during power-down of the game.

>
> > oh, and to replace it -- PIV = peak inverse voltage. It's the amount the
> > diode can stand before it dies -- NOT to be confused with forward bias
> > voltage. You can use any diode with a HIGHER PIV, but not lower... if the
> > orig was 100 PIV, go down to RAT shack and get a diode with 100+ PIV --
> > many go 200, 300, etc. The diode there is non critical in almost every
> > spec except PIV :)
>
> That's what I'm looking for -- that any run of the mill 1n400x will do, or
> if this 1n100 was higher speed or something. Discussions on the list before
> have said NOT to just replace a diode with a 1n400x. Maybe the 100 was just
> cheaper.
>

At first thought a 1N4000 series (even the 50 volt part) should be fine. But on
closer observation...

WHOOOAAA! NO, don't use any silicon diode there, the 1N100
is GERMANIUM! Perhaps a Radio Shack 1N34 or 1N60
could be used. The only thing in silicon even close would be a
Schottky diode like a 1N5711.

The diode has to turn on before the innards of the regulator do.
Germanium turns on at about .2 volts instead of the .65 of silicon.
Schottky is somewhere in between, and you will have a hard time
finding a 100 volt Schottky. But as long as it's good for at least
20 or 25 volts it should be fine.

> Thanks !
>
> -Chris
>
> ==========================================================
> Chris Candreva -- chris@westnet.com -- (914) 967-7816
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Received on Fri Oct 15 03:45:35 1999