2
\$\begingroup\$

I would like to add an offset to a signal to send it on a differential ADC. But i want to be able to control the value of this offset with a PWM. My sensor has a bandwidth of [1-100Hz] and i only have a 0-5V supply.

It works well with offset of 2.5V / 2V / 1V but for 0.512V i have an offset of 4V instead at output. And i don't understand why.

The OP-Amp use is a TL072, maybe it's a limit of that Op-Amp?

If you guys have an idea about how i can fix that or which Op-Amp should i use or an another way to doing that i'll like to hear that !

Thank you ![enter image description here

File:

https://www.catupload.com/download/c5e9aaaa13797a98368cb01dce96e3f5.html

Schematic V2 :

enter image description here

\$\endgroup\$
  • \$\begingroup\$ Can you also share the simulation file so that we can test the same on our end. \$\endgroup\$ – Mayank Jul 21 '17 at 13:12
  • \$\begingroup\$ is that what you asking for? (the link at the end of my post) \$\endgroup\$ – bouaaah Jul 21 '17 at 13:51
  • 1
    \$\begingroup\$ Hint: What are the specs of TL072 with +5 and 0 V supplies? \$\endgroup\$ – The Photon Jul 21 '17 at 14:09
  • \$\begingroup\$ @bouaaah I was asking for *.asc file that you used to simulate the schematic in LTspice \$\endgroup\$ – Mayank Jul 22 '17 at 4:55
  • \$\begingroup\$ I modified the link, there is the .asc file ;) \$\endgroup\$ – bouaaah Jul 24 '17 at 12:46
0
\$\begingroup\$

The input common mode range of a TL072 doesn't get to within 0.5 volts of the most negative power rail (0 volts) in your circuit. That is your likely problem. Try looking for a rail to rail opamp or maybe try an LM324.

Additionally, the minimum recommended supply voltage for that opamp is +/- 5 volts.

\$\endgroup\$
  • \$\begingroup\$ Thanks, I'm not familiar with common mode. I'll try another OPamp asap. \$\endgroup\$ – bouaaah Jul 21 '17 at 14:33
  • \$\begingroup\$ How did it go with the replacement and what device did you choose? \$\endgroup\$ – Andy aka Jul 21 '17 at 18:00
  • \$\begingroup\$ I think i'll choose a TLV2252. what do you think about it? And do you know a website where i can learn more about common mode range? Because i don't know how to use the datasheet to choose my opamp. \$\endgroup\$ – bouaaah Jul 24 '17 at 12:42
  • \$\begingroup\$ The TLV2232 looks OK providing the input voltage doesn't go above 4.2 volts. I'm sure there are websites for learning but I can't particularly recommend any for this other than just trawling thru google with key words. I learnt all this stuff before the internet was conceived so I'm not likely to have used websites for this LOL. \$\endgroup\$ – Andy aka Jul 24 '17 at 13:03
  • \$\begingroup\$ Hahah ok ty ! But i did a mistake, i mean i chose the TL2369, but i was reading the TL2252 when i respond to your comment :p \$\endgroup\$ – bouaaah Jul 24 '17 at 13:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.