"scott93727g" wrote in message
...
Pwr suppley Problem
I made a power supply with 3 paralelled LM338 Regulators in paralell
(24V 12A trans), with 2 paralelled 20A rectifirs, worked great for 1
week, then all of a sudden, output dropped to 2 amps max (from 15A), ,
all componed seem to check out ok, getting full current out of filter
caaps past rectifiers, any ideas, tried substituting a good regulater,
and same thing, any ideas.

The LM338 is a variable monolithic voltage regulator good for 5A continuous.
Did you get the schematic for this PSU from somewhere, or did you come up
with the concept of paralleling up three devices yourself ? If so, there are
various reasons that you might be running into trouble with it. For a start,
you can't (shouldn't ...) parallel up three devices, just by connecting
their pins together. There has to be at least current sharing resistors, and
even this isn't generally recommended as the way to do it. Also, the devices
*must* have suitable decoupling caps fitted around them, otherwise they are
very likely to hoot, which can lead to rapid destruction.

If you need to use these devices to make a power supply with more current
capability than can be provided by a single device, I suggest that you use
the manufacturer's application notes as your starting point. See :-

http://pdf1.alldatasheet.com/datashe...ICS/LM338.html

In these notes, you will see schematics for using multiple parallel devices
correctly.

Good luck with it.

Arfa