Op-amp supply rails and common-mode voltage range considiration.

[David_]

Hello.

I have a circuit with a op-amp amplifying a 0-3,3V signal into -3 to +30V signal, as well as another 0-3,3V signal into +3 to -30V.
First I thought to use a op-amp that could be supplied with +33V/-5V & +5V/-33V, or something very similar. But now I have selected a op-amp that could be supplied with ±30V, so that op-amp(LTC2057HV) could be used with almost equal supply rails. Just offset them slightly to ensure a max +30V output for one and a min -30V output for the other.

Is there anything to gain by using equal or almost equal rails as opposed to use +33V/-5V & +5V/-33V?


I have read a lot about input voltage common-mode range but there seams to be something I can't get my head around.

 

[mrinalmani]

Although you have nothing to lose, you may find it slightly more difficult to split a, say 40V supply into +35 and -5. It will be relatively easier to split a 60V into +30 and -30. However an OP amp working with voltages as high as 60V should be expensive and the price may not be justified over the small difficulty of un-equal voltage splitting.

 

[David_]

Actually the LTC2057HV cost about 5USD, which in my application is not much. The supplies comes from a center-tapped transformer so splitting supplies is not a problem, I will have a LM317s & LM337s or something equivalent so the voltage levels are easy to choose. In the current design I have pots to adjust the voltages but I will change those into resistors. Its all SMT parts.