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



Schematic V2 :

enter image description here

  • \$\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

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.

  • \$\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

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