power supply - senior moment

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ed
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#1 power supply - senior moment

Post by ed »

I've built a number of power supplies like the one shown, at least I think I have.
This one doesn't work. The rail voltages are as shown on the diagram. The Tx is 2 x15v.
it's supposed to supply + and - 12v but the negative rail comes out at -20v ish.

At first I thought I'd got a dodgy 7912 so I bought some more and replaced the one in the circuit....same result, -20v
I've double,triple checked the connections because the pin outs on 78 and 79 regs are not the same...all is good.
Can anybody suggest what I'm doing wrong?
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Nick
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#2 Re: power supply - senior moment

Post by Nick »

Try adding a small load, not sure the reg will work with no current being drawn.
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ed
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#3 Re: power supply - senior moment

Post by ed »

thankyou...12.2 and -11.9
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