Switching PS for S-100 Computer?

If you want a switchmode PSU you have to know what the load will be. That includes the MINIMAL load, which must be within specified limits, else the unit won't regulate. The problem with S-100 is that most of them have a PSU that's capable of 100x the power needed. IF you design a switcher for 100x the power needed, it won't regulate with the 1x load. I have half a dozen S-100 systems, none of which need more than seven or eight slots populated, and those only when I'm using the ultra fast SRAM boards. In most cases, the load on the +8 is about 4 amps and the load on the bipolar 16 is less than an amp. If you use a 22 slot backplane with the idea in mind that you're going to use the 16 4K SRAM boards that justify such an arrangement, you might need a BIG power supply. If you're going to use a 65K DRAM board, as most S-100 systems use, you won't need a big supply. It's all in making up you mind. If you want to use a switcher that you can afford, then you use a PC PSU at the low end, and something intended for a UNIX server at the upper. It has the necessary power and voltages, but requires that you modify each S-100 board by bypassing its regulators. Is that what you want to do? Keep in mind that these boards were designed to work with the on-board regulation. Whereas a HUGE transformer from a distributor may cost $200 a switcher at 8 volts with enough current to cover the most heavily loaded S-100 will cost more than that. You might get by with a heavy duty bipolar 15-volt switcher if it has an output voltage adjustment. A transformer capable of doing the job will cost $25 from a surplus vendor, though it may cost $30 to ship. Isn't that an easier solution? Check with www.mpja.com, www.mouser.com, and the like and see if you don't find a suitable transformer. If you really can't find one, let me know and I'll send you an S-100 PSU for $5 + freight. I'm sure I've got one or two to support between 15 and 21 slots, though they've been on the shelf since the '70's. Dick ----- Original Message ----- From: "Rich Beaudry" <r_beaudry(a)hotmail.com> To: <classiccmp(a)classiccmp.org> Sent: Thursday, August 23, 2001 1:34 PM Subject: Re: Switching PS for S-100 Computer?