[SOLVED] TL081 datasheet offset configuration

[strasni_betmen]

Hi,

in the TL081 datasheet there is a circuit for input voltage offset adjustment.
i don't understand why are offset N1 and offset N2 pins connected to a negative voltage(through a pot)?

if IN+ and IN- pins are both positive, will I be able to adjust the offset
with that offset adjustment circuit from the datasheet?

i have a feeling that this what is troubling me is simple, but i just can't understand it, so
i would appreciate if somebody could explain the offset adjustment mechanism of TL081!

thanks
kind regards

 

[godfreyl]

The offset adjustment works whatever voltage is on the input pins. There's a schematic in the datasheet that shows what the offset pins are connected to internally. If you look at that, you can see how it works.

 

[strasni_betmen]

so for example,

if IN+ = 5V, IN- = 3V, the resulting signal will be 2V and I will be able to shift that resulting signal up or down using the offset adjustment configuration from the datasheet?

 

[godfreyl]

if IN+ = 5V, IN- = 3V, the resulting signal will be 2V

How do you work that out? With such a large differential input voltage, the output will be at Vout(max).

...and I will be able to shift that resulting signal up or down using the offset adjustment configuration from the datasheet?

No, that's much too large.

The purpose of the input offset adjustment circuit is to let you trim the input offset voltage to zero. The maximum input offset voltage for a TL081 is 20mV.

 

[strasni_betmen]

i'm sorry, i left out the context. i'm building a non-inverting low pass filter using TL081, and i'm planning to use it as a voltage follower with RC circuit on the input.

now when you know the story, do you think that i will be able to shift the signal more than 20mV with that offset circuit from the datasheet?

 

[godfreyl]

do you think that i will be able to shift the signal more than 20mV with that offset circuit from the datasheet?

I expect so, but I don't know how much.

Why do you want to do that anyway? Most people want to reduce DC offset, not increase it.

 

[strasni_betmen]

thank you for your help.
i am planning to use it to reduce offset, i was just wondering how come offset reducing works when offset N1&N2 are connected to negative rail. but for now, it's enough for me, i'm gonna jump to some testing...

kind regards