At 12:20 AM 3/31/2010, Bob Blick wrote:

>You are exceeding the common-mode range of the opamp by having 10v/2
>going into each input.

I had considered that but discounted that possibility - several 
op-amps (J-FET op-amps, especially) work just fine with the inputs at 
or somewhat above Vdd.  Take a close look at the spec sheets for a 
TL07x part, for example.

I saw the part number TLC something and assumed that the original 
poster had checked that the common-mode voltage was within the 
operating range of the chip.  Maybe I shouldn't have made that assumption . . .


I've also used op-amps from Linear Technology that allow operation 
with the inputs significantly above Vdd (a couple of hundred volts, 
for one particular part).

dwayne

-- 
Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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