Dave said:
It is indeed. However I'd like the correct nominal voltage for prolonged
soak testing.
Why wouldn't you soak test at worst case numbers rather than nominal?
Certainly depends on the power supply, but there needs to be enough flux
in the transformer to make the outputs work.
If the 5V is the regulated output...or 3.3...or whatever,
and there's no load, there won't be enough flux to make the 12V work at
any significant load.
You're gonna need to redesign the circuit to sense the 12V output
so you can get the current you need. The rest is just resistor ratios.
But wait...if there's no load on the other outputs, you run the risk
of transients charging the caps till they explode.
And depending on the physical location on the circuit board you
pick to connect your new components, you may make significant changes
to the transient response. With high-currents, one point on a trace
ain't the same as another. You can compensate the feedback loop,
but load transient induced spikes can/will cause you grief if your
layout doesn't consider it. Building the transient test fixture
to test your design is non-trivial.
There's an interesting ratio. How much you are saving on the power
supply (including costs of
design/debug/labor/testing/documentation/training)
divided by the cost of blowing up all the stuff connected to it.
And what do you do when it breaks...or you need another one
and the original PS product is no longer available?
Few people understand the subtleties of power supply design.
It's a black hole (art) that sucks in everything around it.
Go buy a real honkin' power supply and use a slew of small circuit
breakers to power your individual test stations.
I don't know your burdened design labor rate, but modifying
PC power supplies is often false economy.
Your time might be better spent
simulating the automotive power
environment for your tests.
littelfuse appnote an9312 is a place to start.
Are we having fun yet?
mike
