pos 12 volts to split 5 volts supply?

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Post by Bern » Thu May 25, 2006 11:06 am

Hi Dacflyer -- This may be too late, but possibly another idea to look at. I haven’t tried it, but a quick thought and scribbles on paper look like it might be worth trying. The only requirement appears that the Pos load always has to be greater than the Neg. load. -------

Take your 12 volt supply and connect to a 10 volt regulator in a conventional manor. At this point leave everything floating. The 10 V output will become the +5 V source. -- Take a Neg 5 V regulator and connect its common to the +10 V output of the 10 V Reg. Tie the Neg 5 V regulators’ input, to the neg side of the 12 V supply. (This is also the 10 V regulator common pin) This will become the Neg 5 V output. --- The output of the Neg 5 V regulator now becomes the common or ground of the final supply. -----------

Now they are acting like normal regulators, and if the Pos load is always higher current than the Neg load, it might do your job. --- You should put in the normal bypass caps, as with any voltage regulators. You mentioned that you tried using two regulators without any success, wondering if yu tried this configuration. Good Luck!!!

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Post by dacflyer » Thu May 25, 2006 8:11 pm

thanks bern , i'll try this also...even just to see if it works

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Post by MrAl » Fri May 26, 2006 6:51 am

Hi there,

That's definitely thinking there Bern! :)
The only thing i'm worried about with this config and even
the one i suggested to try is that if the output of one regulator
appears too much sooner than the other then the circuit could see
a much higher voltage than is expected...
For example, say when the power switch is turned on the +10
regulator starts up and puts out +10 volts which is relative to
actual ground, and say the +5 volt reg hasnt started up yet because
of a slight delay so it's output is still 0.0 volts. This puts +10v to
a place in the external circuit that expected only +5 volts, at least
until the +5v regulator starts up.
Then again if the +5v regulator starts up before the +10v reg then
circuit ground gets +5v on it, so it looks to the circuit that the place
that is expecting +5v gets -5v until the +10v regulator starts up.

Either could have nasty effects, unless the external circuit is
not that voltage sensitive.

It might be possible to use diodes to prevent this kind of situation,
as long as they dont prevent one of the reg's from starting up.
LEDs vs Bulbs, LEDs are winning.

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Post by dacflyer » Fri May 26, 2006 1:38 pm

a six volt zener should solve that problem,,or ???

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