S-100 Power Supply

[woody1000]

Hi All
I have been looking at the 2 power supply options presented on the s-100 computers site.

I want to go with the switching power supplies from Watt Supply. For the +- 16 volts

there are a number of supplies that have +- 15 Volts . The + 15 is rated at 2.5 TO 3 Amps

and the -15 is only rated at .5 amps ( at least 3 amps would be required ).

Refering to the switching supply solution presented on s-100 computers, three supplies were used.

one suppling +- 16 ,one for +8 and one for + 5 and 12 Volts ( is 5 and 12 needed ? ).

I did not find a power supply on Wattsupply that +- 15 volts @ 2.5 to 3 amps. ( is there one ? )

The only other way i can see to get the required current is to buy 2 15 Volt Supplies and wire the output

in series and ground the center point. But this would need an isolated ground.

any thoughts or other solutions anyone else has done ?

I'm not Sure but i thought it was John who built his power supply with the 3 switching units


Thanks

Doug Wood

 

[kyeakel]

An old s-100 computer doesn't have the +5 or +12, they would be be used for more modern peripherals if added. Some of the +-15v supplies can be adjusted up to get closer to the +-18v that was originally supplied, but most s-100 cards use these voltages to generate +-12v if needed. Sometimes -5v is made on the card as well. I used 2 supplies, 1 for the +8 and the other for +-17.5v which was as high as I could adjust it.

 

[Chuck(G)]

Just curious--why 3A on the -12? To the best of my knowledge, that's only used for substrate bias on older MOS devices and for EIA RS232 mark level. Shouldn't be more than a couple of hundred milliamps, tops.

 

[woody1000]

Hi Guys

The design for the power Supply on the S-100 site showed the -16V fused at 3 amps. So i assumed the
current requirements could be higher than the .5 amps on the switching supply ( especially with many cards ).
With the -16 V supply only a few hundred milliamps the switching supplies would easilly do.


Thanks
Doug Wood

 

[monahan_z]

That's the lowest board fuse (of that type), Jamaco had at the time. Except for a few old chips 8080, UARTs etc -16V is almost never used on S100 boards. A typical reason for blown fuse on the -16V line is a dead short, thus thus the fuse.