[sdiy] L7912ACV puts out -16.3 volts

[Dave Krooshof]

>Nothing wrong with two bridges.
>Description sounds like missing minimal load to me. (If there is
>no blatant circuit error.)
>Connect two 1k resistors from +12V to GND and from GND to -12V
>and see if voltages will be right then.

>Dear Dave,
>the l7912 regulator needs to have a small load on it to work correctly ,
>the +v version 7812 doesn't seem to !
>so I think if you put a small load [ 1k res ? ]across each output to
>ground that should work.

that's it.
I left the circuit alone for a night, for regain a clear eye.
I had a 10K load to measure, yesterday.
Checked serveral resistors, the minimum load for the 7912
is in the 7K region, as the voltage starts dropping down from 16 volts.
At 5K it's 12 volt.

I=V/R
12/7K=1.7mA
I guess it's safe to leave the resistor in there. Then I know
the load is already on it's minimum. There's -14 volt over this end now.


As far as the two bridges are concerned, It might be a waste of bridges,
but  IMHO it doesn't matter to much conceptually, where in the circuit
two of the four outs are connected to get a zero.
And since the 7812 is behaving a lot better loadwise, Harry's solution
is going to be in my next power supply:
>If you used two bridges you might use two positive regulators....
>then thie them in series.


Thanks guys, I'm happy to know I can count on debugging advice here.

----- >^v< ---------------------------------------
Dave Krooshof http://www.xs4all.nl/~krooshof
geluidstechnicus @ http://www.ahk.nl/the
webmaster: http://www.popronde.nl
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