i have a 24V dc bus, and i need a +15V and -15V rail for some opamps....how do i create a -15V rail?

i found a chip pt6645, but i cant get ahold of 1.

 

http://cache.national.com/ds/LM/LM2576.pdf figure 10 shows what you want.

 

looks good, going to give it a bash, thanks alot!

 

What do your op-amps do?

It's possible you could use AC coupling capacitors if it's AC or use a virtual earth circuit, if it's DC.

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The op-amps are for signal conditioning (offset/gain) before going into a dsp, so dc application. Another student developed the cards, and I don’t want to go and redesign his work unnecessarily. The stipulate rails for the circuitry is +- 15V, but 12 will work just as well.

 

How much current does it use?

A virtual earth circuit will probably work.

http://www.electro-tech-online.com/e...wo-7805-s.html

http://www.electro-tech-online.com/g...l-grounds.html


Just ensure that all the circuits operating from it that interface with each other all use the same virtual earth for the 0V rail.

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Further to my rather short posting, if you change to an LM2576HVT-15 it will give 15V. If you are only powering a couple of op-amps it is a lot more powerful than you need, but you can use that principle with just about any buck regulator.

 

Charge pump converters are suitable when low power is required. If +/-12 Volts are fine, you can invert +12 V with an ICL7662 or similar (newer?) ICs. Your input voltage limits the choice of the converter amongst few devices, though.

http://datasheets.maxim-ic.com/en/ds/ICL7662-Si7661.pdf