17 Aug
1999
17 Aug
'99
10:22 a.m.
What puzzles me is why the IMSAI folks decided to use a
switching power
supply when the box and everything else already supported the needs of the
S-100 with the previously available and now quite inexpensive unregulated
supplies of yesteryear.
Probably an issue of economy, using PC-clone power supplies at about
$25 each vs using a custom-wound transformer at $200 or so a pop.
One of the main benefits of the S-100 was that it
had on-board regulation, so that if you didn't need a given supply, you
didn't have to bring it on board and regulate it, dissipating power as you
went. If the new box is capable of running the original boards, it must
provide the raw 8 and +/- 16-volt supplies. Where's the benefit in having a
switching regulator sitting in the back of the box? I suppose it creates a
market for a power distribution module to put +5 and +/- 12 on each board
which needs it rather than using the on-board regulators, but that opens
another can of worms. What's the "right" way to distribute it without
tampering with a historically correct board?
According to what I read from the web page, there's a PC-clone switching
power supply followed by a "boost" switching circuit to get back to
+8 and +/- 16. That's not completely unreasonable, but it sounds a
little bit fishy to me in the sketchiness of the details.
Several S-100 manufacturers who were still at it in the mid-80's had
regulated +5V on the S-100 backplane. Those who wanted to use their
older S-100 cards in such a machine just jumpered across the 7805's and
viola!
--
Tim Shoppa Email: shoppa(a)trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927