Re: S-100 prototype boards
- From: "John_VC" <john_vc2004@xxxxxxxxxxxxxx>
- Date: Thu, 28 May 2009 01:27:32 +0100
Hi Andrew, thanks for your work on this project, I hope it goes well.
"lynchaj" <lynchaj@xxxxxxxxx> wrote in message
news:dbd7c066-bd70-4bbd-af74-c4a97e642533@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
The N8VEM S-100 backplane is already out and seems to be OK. Yes, its
off to a slow start but that is not unexpected. Probably the N8VEM
S-100 prototyping board will be too. After that, I intend to design a
simple PCB for a linear power supply.
Do you mean an unregulated power supply with just a mains transformer,
rectifier and smoothing caps? Linear implies some voltage regulation. I
would suggest moving to low cost switching regulators, eg LM2678 (5A).
For 5V and 12V regulators on S-100 cards I would suggest switching
replacements for 7805 / 7812, such as PT5101 or 7805SR / 7812SR. These may
cost more but save on total power needed, and can run with minimal
heatsinks.
You can make your own linear power supply or you can substitute
SMPSUs. I've done those and they will work however they are both
difficult and/or expensive. I managed to cobble an S-100 power supply
together using repurposed SMPSUs and it works OK and I've repaired
repurposed linear power supplies. The main issue with S-100 power
supplies, IMO, is they are typically custom solutions. I do not know
of an off the shelf solution with S-100 compatible voltages short of
buying an old one from eBay or buying two or three SMPSUs.
With switching regualtors on S-100 cards you can feed in higher DC voltage
on the bus (say 15V) in place of both 8V and 16V.
Personally I would use a PC ATX PSU (£10 in the UK) to provide 12V DC @ 10A,
regulate this to 5V on each card, and remove / bypass any 12V regulators (as
5V is likely to be more critcal than 12V).
BTW Herb has covered some ground here before:
http://www.retrotechnology.com/herbs_stuff/s_term.html#regulator
As Herb points out, running 5V along an S-100 power supply bus is asking for
trouble, as a PCB bus is a poor way to transport power cleanly from PSU to
the furthest card. If you are designing a system you have to consider the
power supply from the start. To avoid things like a 1V drop from PSU to end
of the bus, one engineering overkill homebrew solution would be to have a
PSU with short thick leads to two big bolts (+ and GND) for the main high
current supply (at whatever voltage needs the most amps), and run individual
thick insulated wires soldered a short (10mm) track from each S-100 socket,
with the other end connected via a tag to the PSU bolt. This would reduce
noise and voltage drop from one card affecting another's supply.
Just my 2p,
Regards,
John
.
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