OPAmp Power supplies

[mwminor]

Hi there,
I've come across a couple of circuits which contain OP Amps the power supplies for which are not connected directly to a +/-15V supply but rather through small - 100 Ohm - resistors.
Is this for some kind of current limiting purpose...? The OpAmps in question are OPA128 - very low current devices - would 100 Ohm provide any real protection anyway..?

 

[Resqueline]

It could be, but I suspect their main purpose would most likely be for noise isolation/protection. I'd expect capacitor decoupling to be present near the OPA.
The Power Supply Rejection Ratio does not reach its maximum of 120dB if PSU noise above 1Hz exists on the negative, or above 100Hz on the positive supply.
BiFET op-amps can be destroyed if they lose their negative supply.

 

[davenn]

Yes, many OP-Amp circuits I have used over the years use 100 Ohm resistors in the supply lines to each chip.
I understand its for a bit of power supply conditioning to balance the current in each supply pin.

D