# Generating -10V or -12V @ 500 mA from +12 / +24V

I am designing a scaling op-amp circuit that requires approximately 500 mA of -10V power (-12V would be better so I don't have to rely exactly on a rail-to-rail op-amp). The circuit is scaling multiple -10V to 10V inputs by 0.10 (output = -1V to 1V).

However, the only power inputs I have available are +12V and +24V (5A and 10A, respectively). Is there a straightforward way to generate the required negative voltage rail? This is not as obvious as I had hoped, especially at the required power (I need to do this across 5 inputs, so all told worst-case is 500 mA).

• If you only want to attenuate the signal, is a resistive divider enough? You might be able to do without the op amps entirely. Bear in mind that this would lead to a high output impedance, so if you don't have any sort of buffer after it (which would require a negative voltage supply anyway) it can't drive a low-impedance load. Commented May 3, 2017 at 4:13
• Alternatively, if you can handle increased power supply noise, you could use the 12V power supply as a -12V supply, if it's isolated and capable of sinking current. Just connect its positive terminal to earth and its negative terminal becomes -12V. Then connect the negative terminal of the +24V supply to the negative of the 12V supply to get a +12V supply out of it. Commented May 3, 2017 at 4:17
• An inverting switching converter would be a pretty straightforward solution. Commented May 3, 2017 at 4:24