Re: Need help with level shifter

On Wed, 11 Mar 2009 15:45:12 GMT, ehsjr
<ehsjr@xxxxxxxxxxxxxxxxx> wrote:

Bob Masta wrote:
On Tue, 10 Mar 2009 03:08:39 -0700 (PDT), aleksa
<aleksaZR@xxxxxxxxx> wrote:


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...


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
www.daqarta.com
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+12---+---[10Vreg]----> +5 --------[Circuit]---+
| |
+---[5Vreg]-----> New ground ------------+
|
Old ground -----------> -5 --------[Circuit]---+

How will the new ground sink 6A from the +5 volt line?


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... <g>)

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
.

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