[sdiy] L7912ACV puts out -16.3 volts

[Dave Krooshof]

Hello,

I just made a powersupply that is supposed to put out -12 and +12 volts.
The + side is OK, it gives 12.1 volts.
The - side is wrong, as it puts out 16.3 volts.

The powersupply consists of a 230 volt to 2x 15 volt transformer.
It puts out 2x 18volts AC. *
The circuit has 2 diode rings (bridge cell in english?), 2 elcos 1000µF,
4 104 caps, a L7812CV and a L7912ACV for + and - voltage regulators

What has gone wrong?
- Was my 7912 off when I bought it?
- did I make a wrong connection that causes it to shift? (I checked and
rechecked, but who knows...) The 7912 connects differently from its
positive brother: 1=left=ground, 2=middle=in, 3=right=out.
- Has my over-enthousiastic trafo just fried my 7912?
- Is 18 volts to much for a 7912? I couldn't tell from the data sheet.
(which is here: http://www.st.com/stonline/campaign/gold/linear/stpos.htm )


Thanks a lot in advance for the responses.


Dave




* Why the hack can't they make stuff like trafos that behave
according to the given specs? (or boxes that say what the inside will do)

Pierce: War is hack.

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Dave Krooshof http://www.xs4all.nl/~krooshof
geluidstechnicus @ http://www.ahk.nl/the
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