I have an old PC power supply:
+12V 9A +5V 20A-5V 0.5A
-12V 0.5A
and what I need is:
+5V 6A-5V 6A
Can someone guide me in the right direction? Am I searching for the "level shifter"?
A schematic would be great, of course...
You can use a buck-boost converter to generate -5V from either the +5V or
+12V lines:A real circuit will be rather more complex than shown there, due to the need to regulate the output by varying the duty cycle.
Search for datasheets for "switching regulator" ICs. They will contain example schematics.
No; a level shifter shifts the voltage levels of a signal. It requires that you already have a DC supply at the desired voltage.
A level shifter is a device that operates on signals. You need to actually transfer power, a job for which you need some sort of switching supply.
You either need a negative switcher to tack onto your generous supply of
+12V or +5V power, or (since you're proposing to build one anyway) you need to go out and buy a switching supply that does what you need without the false economy of putting $$ worth of parts onto that 'free' supply you have.Check Marlin P. Jones
-- http://www.wescottdesign.com
Get another old PC power supply & use its +5 inverted (be sure to isolate). Bob
While I fully agree with the other posts that recommend a "real" second supply or a switchmode regulator, just for completeness there is a way to use a "level shifter" to do *sorta* what you want.
The idea is to take the +12V supply and run it through separate +5V and +10V regulators, then use the common ground as -5V, the +5V output as ground, and the +10V output as +5V. You would have to be *very* careful to keep the original ground (which you are now calling -5V) away from the new output ground. The new ground thus can't be connected to the chassis, etc.
In general (and probably in this case), this would be a really dumb approach. But you should keep the general concept in mind. In the more usual case, you have a single supply like +12V and you want to split it into +/-6V to provide a central ground reference for a few op-amps, and maybe drive a modest load with a bipolar swing. This is usually called a "ground splitter". You can just use an equal-resistor voltage divider on the 12V to get 6V, then use an op-amp buffer (possibly with a pass transistor or two in the feedback loop) to provide the ground for an external load.
Just something to keep in mind for future reference.
Best regards,
Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis
+12---+---[10Vreg]----> +5 --------[Circuit]---+ | | +---[5Vreg]-----> New ground ------------+ | Old ground -----------> -5 --------[Circuit]---+
How will the new ground sink 6A from the +5 volt line?
Ed
As it turns out, 5V is not enough, and I will probably buy two 7.5V units.
Thanks, everybody.
OOPS! You are right... should use only the +10V regulator, then use a ground splitter on that. The splitter will need to be able to source and sink current, so the op-amp buffer will need two pass transistors in its feedback loop. (This was actually what I was going to suggest originally, but the 5V regulator seemed so much easier... )
Best regards,
Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis
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