Generating negative supply.

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#1
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Hi guys,

i need to generate a negative supply -5v for an opamp, i dont need more than a few milliamps of current.

i have already have a 5v power rail and gnd.

whats the easiest way to do this?

also a clean output would be preferred. and also a low noise output would be nice as well.

thanks.

- Tony B. Sydney, Australia.
tbaz2679@mail.usyd.edu.au

Status: Supporting the GNU

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Anything here helpful? Not used the parts myself, but have used their level shifters and other DC-DC smps.

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This page has useful information about different methods of creating +/- power supplies from a single voltage source: http://tangentsoft.net/elec/vgro...

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I have used the ICL7660.

http://www.maxim-ic.com/quick_vi...

I needed to generate +/- 5VDC from a 9V wall wart power supply. I connected the battery to the ICL7660 and then used a LM79L05 on the output of the ICL7660 to get the -5VDC and a LM78L05 connected to the 9V line to get +5VDC. I know that is overkill, but costs were not a real issue, especially considering it was probably less than $2 for the addition of the LM79L05 and its associated capacitors. I was only building 25 units.

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How about the MAX232?

Ross McKenzie ValuSoft Melbourne Australia

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Ive decided to use the simple charge pump from texas partnumber TPS60403. cheap.

Now, i want to connect it to my opamp, just an lm741, also cheap, and use it to measure the drop acros a low ohm resistor on the gnd plane to measure current.

do i need to regulate that voltage to a clean -5 volts or is it ok with a small ripple there?

Also, is the lm741 good for current sensing? should i use something better? what could be more accurate?

thanks for your quick help guys.

- Tony B. Sydney, Australia.
tbaz2679@mail.usyd.edu.au

Status: Supporting the GNU

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If that is all you needed the negative supply for, just get a rail to rail single supply op amp. This will handle inputs from Vcc down to GND and the output will swing from Vcc to GND too. :D No need for the hassle of the negative supply.

The 741 is not a good opamp. You need a precision opamp for this - low offset voltage, low drift. Search the forum for related threads - this is something that is often asked and discussed.

If you think education is expensive, try ignorance.