OP AMPS... Common Mode Input Range Inquiry

Thread Starter


Joined Oct 31, 2006
Hi Everyone,

I would like to inquire or clarify about the characteritic of the OP-AMP,
which currently Im making High Current Side Sense Circuit at the
secondary side of my current power supply design, and Im planning
to use an OP AMP as Non-inverting amplifier sensing the voltage across
the sense resistor and amplify it.... And my inquiry is that the Common
Mode Input Range must be always less than the VCC of the OP AMPS?
If yes, what is the explanation? IS there any available OP AMPS that
could accomodate higher range of Common Mode Input Range greater
than its' VCC?


Joined Feb 24, 2006
The common mode input range is determined by, among other things, the differential input stage. In bipolar input stages your common mode input range might actually be less than the difference in the supply rails by 1-2 Volts DC. It is not uncommon to use +/- 15 Volt supplies when all of your inputs and outputs are limited to +/- 10 Volts.

There are other kinds of input structures which allow a closer approach to the rails, but going beyond them is not something I've encountered. These devices are called "rail-to-rail". You have to read the datasheets carefully to see what they will and won't do. Expect to pay substantially more for them however.


Joined Apr 20, 2004

Sorry I can't cite the part number, but I do recall a manufacturer that makes a high side current sensing ic. I'm sure it would be less trouble to use than an op amp. You might look at the Linear technologies site for the device.