Electronic – Op-Amps with unequal split supplies (e.g. V+ = 25V, V- = -11V)


Most electronic designers will be familair with designing op-amp circuits with a single supply rail (e.g. Vs+ = 5V, Vs- = 0V) or matched split supplies (e.g. Vs = +18V, Vs- = -18V).

I have a design where I need to handle both +24V inputs and -10V inputs. Of course, there are some off-the-shelf parts that can handle +/-40V supplies, but my choice is rather limited.

On the other hand, op-amps with 36V supply voltages are plentiful, and given my voltage span is +34V, a carefully chosen rail-to-rail input/output (RRIO) op-amp should be up to the task, if I can make the supplies +25V, -11V.

This would make the design rather unusual (to say the least). What do I need to pay particular attention to when designing for this unusual arrangement of supply rails? Or, am I simply better off going for the high-supply op-amp?

EDIT: Do I, for example, need to take into account the following:

  • A higher than normal offset voltage/bias current?
  • Problems with matching between bias current and/or offset voltage between channels?
  • Changes to distortion?
  • Any other likely specification changes?

Best Answer

It's fine as long as you don't go outside the common mode input range.

Remember that the op-amp thinks only in terms of V+ and V- applied. It doesn't care what you call ground.