S-100 Power Supplies: thanks!

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Aug 29 15:28:00 2001

It's 6.3 volts * SQRT(2) less two diode losses. If one uses a SCHOTTKY bridge
with a really low forward voltage, and uses the low-dropout regulators (LM330T)
in place of the LM309's or LM340T-5's, one can use a heater transformer just
fine. The empty slots won't need much power and, unless you use 16 of the old
4K SRAM boards, your power requirement will fall within what that 12Amp model
can do.

One shouldn't try to save on the filter cap's though, and, BTW, and should put a
very low value (~0.25-ohm) resistor between the bridge and the filter caps to
protect the diodes at turn-on.

If there's a real need for lots of power, one can parallel two of these heaters
provided the phase is correct. I've got one transformer downstairs that is
about he size of half a watermelon, weighs on the order of 35#, and has all the
requisite voltages plus a few others I decided I didn't need. I also don't look
forward to lifting it.

Dick

----- Original Message -----
From: "Don Maslin" <donm_at_cts.com>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, August 29, 2001 1:02 PM
Subject: Re: S-100 Power Supplies: thanks!


>
>
> On Wed, 29 Aug 2001, Rich Beaudry wrote:
>
> > Date: Tue, 28 Aug 2001 21:53:29 +0100 (BST)
> > From: ard_at_p850ug1.demon.co.uk (Tony Duell)
> > Subject: Re: S-100 Power Supplies: thanks!
> >
> > >Have you considered winding your own transformer.
> >
> > Uhhh ... hadn't thought of that! :-)
> >
> > > In the UK we can buy 'transformer kits'.
> >
> > Did a quick search of a couple of distributors, but no luck yet ... I'll
> > keep looking, though!
> >
> > >According to my calculator, 6.3V * sqrt(2) = 8.9V or thereabouts. Since
> > >the 8V line is unregulated anyway, I would think you could start with a
> > >6.3V transformer. Can you really no longer buy valve heater transformers???
> >
> > !_at_$#!@$!!~!!!!
> >
> > I found a couple of 6.3V transformers, one at 8.8A, one at 12A ... I must be
> > going blind... I don't think they'd power my 21-slot backplane, but I do
> > have a couple of smaller ones that would probably be just fine...
> >
> > Rich B.
>
> If you get one of those, Rich, get it on a returnable basis. Some S-100
> cards are really picky about the voltage that the regulator chip sees
> and if not high enough will not function.
>
> - don
>
>
>
Received on Wed Aug 29 2001 - 15:28:00 BST