Op Amp Rails Question

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turjohn

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I've got a board that brings in 15V from an external supply and then I am generating -15V on the board with a chip from Maxim but it doesn't seem to want to work consistently from board to board so I am looking at an alternate solution from Linear. They've got a voltage inverter using a charge pump that I've breadboarded and it seems to work fine, except it doesn't give you exactly the negative of the input voltage, when I feed it 15V I get about -14.3V out. My question is this: what effect will this have on my op amps, if the positive rail is at 15V and the negative rail is at -14.3V? I don't plan on my signals going rail to rail, but will unbalanced rails introduce some offset at the outputs of the op amps?

Thanks in advance...
 

The effect will be that signals that are referenced to earth, will appear to the op amp as referenced to +.35 V, which is nothing. If the line differential was huge, say +15 and -6 then the common mode voltage of the input stage could be exceeded.
Frank
 
As long as the signal at the inputs is within the common-mode range of the op amp then a difference in the plus and minus voltages will generally have negligible effect on its operation.
 
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