[SI-LIST] Re: DC Power supplies Connected in parallel
- From: "A. Ingraham" <a.ingraham@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 13 Aug 2012 11:13:30 -0400
> What happens when 2 DC-power supplies are connected in parallel which has 2
> different voltages let say one has 12V and other has 5V.
Because this sounds like a question from a beginner (one who is just
learning about electronics) ...
What happens depends entirely on the design of the two power supplies.
There are many possibilities.
They could design a power supply like an audio power amplifier,
meaning that it tries to make 5V (or 12V) no matter which way the
current needs to go. Then you would have two power supplies
"fighting" with each other and Ohm's law predicts very large currents
from one supply into the other, until something blows or melts.
But most power supplies are not made this way. Usually they need to
supply current to the load only (for positive voltages) because the
load's voltage normally doesn't get higher than the power supply that
is feeding it. So you can think of them like an ideal Thevenin
voltage source in series with a diode: current goes only one way. In
that case, the power supply with the higher voltage "wins" and the
lower one is effectively "not there" and has no current.
Real power supplies could be either of these, and more. As already
noted, some come with over-voltage protection which adds another
factor into the picture. And all real power supplies have voltages at
which they "break" if you connect them wrong.
Paralleling power supplies with the same voltage is tricky enough, let
alone trying to do it with two intentionally different voltages. One
would never use two supplies with distinctly different voltages, in an
attempt to get more current, which is what I think you asked.
In a nutshell, there is no one answer, no one result to your question.
By the way, this has nothing to do with Signal Integrity. While there
are many experts here, this is not the right place to ask that.
Andy
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