Op-amps. A query...

Thanks Ivan

Hi DragonForce,
all is correct. Unbalanced PSUs with both plus and minus, but with different absolute value of voltage, are uncommon, though.
If the output swings around zero volts, an output capacitor is not required at all.

Your questions are not silly at all !

BR from Ivan

Sorry if these questions seem silly, I agree that the answer seems obvious, but I don't have the equipment to test the theory and besides, maybe some other people will gain something from the answers too.

First - I've seen references to "balanced" split rail power supplies. I understand that if you have a split rail supply, the output of the op-amp can swing below zero volts and give a true AC (as opposed to varying DC) signal at the output. Am I correct in this?

If the power supply is un-balanced, the output of the op-amp can swing above and below zero volts, but only so far as the power supply allows. For example, say we have +10V and -5V on the supply pins. Assuming the op-amp can swing rail to rail, the best I can hope to get from the output at any given moment in time, is an AC signal of between +10V and -5V - is this correct?

Assuming that the op-amp is a rail to rail output type: If I use a +10V single rail supply on an op-amp, I can achieve an output of between zero and +10V at any one time. Assuming this to be correct, if I then power that op-amp on a +/- 5V supply, I can still achieve a peak to peak output of 10V. This is to say, I can swing the output between + and - 5V.

If the output is swinging above and below zero volts, what of an output capacitor? I assume a non polarised should be used?

Please forgive my silly questions