On Fri, 4 Jul 2008 01:20:49 -0700 (PDT), angus.oliver@[EMAIL PROTECTED]
wrote:
>Hi All,
>
>Having found dual op amp packages around a fifth the price of
>comparable single packages from online distributors, I think i'll go
>for the double.
>(BTW, I'm using supply of +16, and ground).
>
>I don't want the unused channel drawing current unnecessarily though,
>or bouncing the output around.. - If I tie the non-inverting input to
>+3.3V, and have a high resistance feedback resistor to the inverting
>input (with no other input to that pin), would that be as good as
>anything? I figure the output won't have to 'try' very hard to modify
>the voltage of an input pin with no other voltages on it..
>
>Am I right?
>
>Thanks..
Yup, keep it closed-loop, away from the rails. You don't need the
resistor, just connect the output to the IN- input. 3.3 volts on the
IN+ input should be fine for any opamp.
Some, maybe most, opamps draw a lot of extra current if railed, so
don't tie the ni input to V+ or V-/ground. Some will even mess up the
other amp sections if one section is run open-loop.
If you don't have a suitable dummy voltage handy, and the signal isn't
really fast, you can use the extra opamp section as a follower of the
section that you do use; that keeps it happy, too.
John
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