# Opamp compensating circuit

While reading a book on opamps I came across this output offset voltage compensating circuit.

They used thevenin's circuit looking at Ra from point T:

Then they converted a part of the first circuit the this:

But what I don't understand is how can the given circuit can have both resistance Rmax as well as voltage Vmax at the same time? Why have they shown both the things together in the same circuit. Like if the resistance were Rmax, voltage would have been zero at point T. Can anyone explain please!

Thanks!

• This method is doing things more complicated than they need to so in my opinion this is a very bad example to show DC offset compensation. What they're doing is using a resistive divider circuit to add/subtract a DC voltage to the - input. It is easier to explain if this voltage was applied to the + input as then it will not interfere with the input signal. Using the opamp in open-loop (no feedback) like that only works in theory, try this with a real opamp on a bench and you'll notice how it is impossible to get the output at 0 V. Noise and thermal effects will prevent that. – Bimpelrekkie Sep 23 '19 at 6:25
• If you want to learn about opamps I recommend reading the free ebook, opamps for everyone: web.mit.edu/6.101/www/reference/op_amps_everyone.pdf and also watch the videos made by Dave from the EEVBlog: youtube.com/… – Bimpelrekkie Sep 23 '19 at 6:27