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-ve from a +ve rail?

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b.rad

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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.
 
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.
 
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.

https://www.electro-tech-online.com/threads/5v-supply-from-two-7805s.39621/
virtual-earth-gif.19542

https://www.electro-tech-online.com/threads/headphones-amplifiers-and-virtual-grounds.41122/
virtual-earth-low-pwr-gif.21398


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

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.

https://www.electro-tech-online.com/custompdfs/2008/09/ICL7662-Si7661.pdf
 
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