op amp power rails

[Wp100]

Hi,

Would apprieciate some advise on an op amp question.


An existing op amp circuit fed from split rail supplies of +/- 5v, inputing about +/- 10mv and outputing +/- 1v.

If just the -5v rail was reduced by 5% to 4.75v would the output signal of +/- 1v be changed and if so, would it be just on the negative side or the whole signal ?
( its not my circuitry so cannot actually test it )


thanks.

 

[Papabravo]

As long as there is some room between the output level and the supply rail the effect should be minimal. Everything changes as the output approaches the supply rail and other more subtle changes may occur as one or both supply rails collapse. AFAIK it would be possible to run your application with +8V and -4V or any other non symmetrical combination where there was sufficient headroom between the output peak and the rail.

 

[Wp100]

Hi PB,

Thanks for that.

 

[MikeMl]

Not enough info to answer. If the voltage applied to either the inverting or non-inverting input is developed from a resistive network which has a connection to the -5V rail (or the +5V rail), then a change in the rails will cause a proportional level shift in the output. If the inputs are connected only to external signals, ground, or a regulated voltage reference, then there will be only a tiny shift as the supplies vary. Look up the Power Supply Rejection Ratio (PSRR) for the subject opamp.

 

[Wp100]

Hi Mike,

I do not have the circuit or board, but will pass the info back to the owner.

The point to be made here is do not change anything unless you are 110% sure !

thanks again