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LM338 (x3) power supply cuts out on high loads

The 700,000uF worth of capacitance is connected to the output of the regulator not because I'm try to filter the output, but because I am trying to charge the bank of capacitors for a completely different purpose.

I am now finding that. With this discussion especially, I know I need to lower the voltage into the regulator. Is there an easy way to do this without having to buy a new transformer? They are somewhat difficult to locate for a reasonable price in my area, at least at surplus prices which is about the only option at this point.

Would half-wave rectification be an option? I know I would probably need even larger filter caps, but if it lowers the voltage to a reasonable amount (but not too low...) I would save myself the trouble of trying to find a different transformer.

Thanks Kevin

Reply to
keebler65
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Please ignore the troll. Better yet, just kill file him.

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

National's

of

what

load,

very

make a

limit.

the lm317 ciruit you mentioned will probably do quit well, it needs one pnp transistor wich drives the 2n3055s. carefull to ensure its got adequate current limiting.

or roughly something like this ... used to apear in many op amp application notes ... however linear supplies are probably considered old hat now.

30v___________________ | | | | ____|/ | | | | |e | | | | |__|/____|/___|/ | |e |e |e | | | | | Re Re Re |__Z/|____|_____|____|________ op | Z\\| | R3 R1 | /|______| |_____/-| | \\+|->pot | \\| R2 | 0v______________|

4 x 2n3055 on suitable heatsink. (first transistor could be something smaller) Re=3ohm and zener = 3v for aprox 3 amp current limit, change to suit, max current =3x5 amp due to SOA Re needs to be suitable power. op amp could be lm358, pot needs to be a potentiometer conected to a reference voltage chose r1/r2 for the right op range. R3=1k ish.

also a second op amp could monitor the current ie average voltage accros all

3 Re and take the place of the zener.

If you not capable of debuging its best to find a design with more detail, im sure there must be some out there, or simulate it first with ltspice etc.

ooh a quick search showed up this ..

formatting link

Colin =^.^=

Reply to
colin

If charging speed is not an issue, just use a big R - say

50 ohms (2 25 ohm resistors at 25 watts each, in case you short the output somehow) - between the bridge and the regulator. That will be kinder on the bridge & the xformer, and you won't need 3 parallel 338's. It'll take a few minutes to charge. (You could use a much smaller xformer and save the 15 amp beast for a better purpose.)

Ed

Reply to
ehsjr

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