Electronic – Using an opamp with fractionnal gain with supply less than input signal

gainoperational-amplifier

Let's say we have an AC signal that can swing from -15v to +15v max peak to peak. If I use an opamp with the power rails to -5v and +5v, can I get a non clipped output signal if I use a gain of 0.333? Or will op amp failed to recognize anything above/below +/-5 V at it's input even if the required output is within range?

Do I need to have my opamp's power rails and specs within the input range or the output range provided that the output have less peak-to-peak swing than the input with my gain of 0.333?

The signal I'm talking about is a low, signaling level (about 1mA max) with varying frequencies, like an audio signal.

Best Answer

The op-amp will have a common mode input range specification. This means that there is a range of voltage relative to the supply rails in which you need to keep the inputs for the op-amp to function correctly. For example, with LM324 you can take the input down to the negative rail but not within 1.5V of the positive rail. If you use an inverting amplifier configuration then the inverting input of the op-amp is a virtual earth so you might have 0V on both inputs, even with a 15 V signal. A non-inverting configuration where you apply the signal directly to the non-inverting input would not work.