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Re: Power distribution across an S100 Board and voltage issues with TO-3 Regulators..

Hi all,


If I may offer a suggestion on getting reliable DC voltages at decent amperage, I’ve always scrounged and recovered parts and components wherever I could as long as I can remember, and the best source of parts I've ever found is old Telco line cards and DSLAM gear. As all Telco’s are continually upgrading exchanges and equipment, it leaves a lot of old cards and sometimes VME style chassis’ that get scrapped. These are a fantastic source of DC-DC converters, relays, TTL, inductors, switches, EPROMS, etc. The DC-DC converters are probably of most interest here, as there is generally several of these very high performance switch mode converters per card, 24-72V in, 12V, 5V and sometimes 3.3V out, at 3 to 5 amps. They run cool, and work a treat, and are rock solid on their output. Some of these new are around $50, up to $200 each for the Lambda ones! This is an example of the simple 4-5 pin ones I retrieve:



I’d highly recommend finding and getting to know your local DSL or Telco stores guys to swap beer with them, as they’ll likely be the ones organising the recycling of these cards. They are a veritable gold mine of useful parts.

Another bonus is that all these cards also have chassis eject levers on them!


Cheers, Ian

On Tuesday, June 3, 2014 5:01:57 PM UTC+10, monahanz wrote:
Does anybody know how much tolerance 74xx TTL chips have to a situation where on the LHS of the board near the V regulator is  5.13 volts while on the extreme RHS the voltage has dropped to 5.03 volts.  This is the new 80386 board which draws a fair amount of current. 
See here:-

I am using a 78H05 TO-2 regulator (Fairchild).   Even though these regulators are hard to find, with their heat sink they run nice and cool. Is the above acceptable both in terms of voltage gradient and absolute number i.e. >5V.

 While on TO-3 5V regulators, I have been plagued with "no name brands" that either quickly die or are way outside what they should be in terms of voltage.
Just yesterday I got 2 "LM323K's (5V, 3A) from Unicorn. One put 6.2 volts on a test board!!!!   I had others from Jameco that put out 4V's.

Since a couple of our recent S100 board use these regulars, please test them first. Mouser stopped carrying the LM323's. If anybody has a good source to name brand 78H05's or LM323's please let us know.
I'm reluctant to go with two L7805ACV's TO-220 (5V 1.5A) because they use up so much board space with their heat sinks.