Other Parts Discussed in Thread: LM393, LM358
In continuation of previous thread: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1166946/tl082-schmitt-trigger-not-cutting-off-at-set-threshold/4389144
I have made a circuit like this:
(A slight correction that supply voltage is 20.4V and NOT 20V, all resistors are of 0.1% accuracy)
This circuit is a schmitt trigger having upper threshold at 1.15V theoretically as non-inverting input should develop 1.127V. I have a variable current source at inverting end passing through a resistor to develop a voltage to be compared.
But when I built the circuit using LM393, a comparator opamp, I got 1.074V at non-inverting pin. I thought maybe it is because of input bias current of non-ideal opamp. Anyways now it should toggle the output when inverting terminal voltage reaches 1.074V . But as I increased the current slowly I saw that opamp is toggling at 1.7mA which corresponds to 1.7mA*560ohm = 0.952V which is lesser than 1.074.
Now when I replaced the opamp with LM358, a general purpose opamp, the non-inverting input was found to be 1.14V and ouput toggled when current is 2.02mA which means at inverting voltage of 2.02mA*560ohm = 1.13V. Which is much better performance than LM393.
I am not able to understand that in previous thread I was suggested LM393 which is comparator opamp, it is working poorly than a general purpose opamp, what is the reason? Why LM393 not togging exactly or nearby its threshold voltage? Also my circuit is little critical and I need to toggle the output at 2.01mA so should relying on LM358 a general purpose opamp be feasible?