Hi, Basic question I guess: consider the following circuit - A current source connected in serial with a resistor R - both between the "in -" and "in+" of an opamp. the "in - " is connected to the opamp "out" via a resistor R1. the "in + " is connected to the opamp "out" via a resistor R2.
what is the output voltage?
i seem to be reaching a contradiction using the ideal opamp model. How is this settled?
Thanks !
Well duh! It's unstable... positive feedback.
...Jim Thompson
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I love to cook with wine. Sometimes I even put it in the food.
By not asking stupid twat questions..... Would you care to explain why you have not asked a stupid twat question? You might start off by giving the sums you have used to reach your contradiction.
On the other hand you might just float away.
DNA
I understand,
Thanks alot!
Especially thank you, Genome, for the helpful response.
It will settle right on the rail, since the circuit is useless. Look how the current flows from the output back into the output, it is independent of the output voltage, thus there will be always a voltage between +in and -in, overdriving the opamp. but you can at least know what direction the PD was connected.
-- ciao Ban Apricale, Italy
Amplify Notice that nowhere in your circuit do you have a ground connection--that is, a point of reference for measuring the op amp output voltage. Since the inputs of your ideal op amp are infinite resistance, then the current source just pumps current around the loop R, R1 and R2. The op amp output voltage, no matter what it is (in an ideal case), can't deliver current to R1 or R2, since there's no path from it to ground through either of them. What is the voltage drop across R1+R2? What is the voltage difference between the op amp + and
- inputs? What's the op amp open loop gain?
Cheers, Tom
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