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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Pwr suppley Problem
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. |
#2
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Pwr suppley Problem
"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 |
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