[sdiy] power supply pain

[Jim Patchell]

Gavin Russom wrote:

> Hi there
> So I built my own power supply for my modular (which I know everyone
> reccomends AGAINST)

        Not me ;^)


> but the reason I did it was because I needed +12, +9,
> +5, -5, -9, -12 outputs but couldn't find a suitable one for sale.  I built
> it and it tests perfectly at all the outputs.  But when I hook it up to my
> ADSR that runs off +5 the voltage immedeately drops to about +2.2 volts,
> even if i test it at the output of the power supply.  If I run the ADSR off
> a 9volt battery it works perfectly, but if I connect it to the +9 of the
> power supply again the voltage drops to about +4.3 volts even at the supply
> output.  If I hook up the ADSR to the +12v out put the voltage doesn't drop
> but its too much voltage for the ADSR.  The power supply uses a 7812 to get
> the +12V, then taps off a resistor network to get the +9, and goes through a
> resistor network and a 7805 to get the +5.  The variable voltage source
> that's tapped off the same resistor network works great no matter what its
> hooked up to.   Any suggestions?   I'd even buy one at this point if it had
> the right outputs, but I'd rather fix my own!
> thanks
> MYSTIC

    Look at the voltage on the input of the 7805.  If it drops below 8 volts,
the output will go out of regulation.

    Generally, using resistors to get the power supply voltages you need is not
a great idea, because the output voltage will vary with load.

    If there is a way we can see the schematic, it would help in solving your
problem.

    -Jim