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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).

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    \$\begingroup\$ 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. \$\endgroup\$
    – Hearth
    Commented May 3, 2017 at 4:13
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    \$\begingroup\$ 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. \$\endgroup\$
    – Hearth
    Commented May 3, 2017 at 4:17
  • \$\begingroup\$ An inverting switching converter would be a pretty straightforward solution. \$\endgroup\$
    – uint128_t
    Commented May 3, 2017 at 4:24

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There are plenty of devices that can do what you want. Try searching for "inverting buck converter". Here's an image I found: -

enter image description here

You could even buy an isolating DC to DC converter and tie the positive output to 0 volts - this then gives you a negative 12 volt output. Also, flyback converters are useful for converting positive input to negative output.

The devil is in the detail (as with all switching regulators) so do a bit of research to check that any schematic offering can regulate from the range of input supply voltages you have specified.

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