1
\$\begingroup\$

I am trying to build an op-amp circuit for a Hall effect sensor. The Hall effect sensor has an output range of 2.01V to 2.87V, and is fed to the Vin of the op-amp circuit below. The output V_out range is measured to be 3.71V to 0.81V. The 3.71V is largely off from calculations, which should be near 4.8V. The op-amp unit is a MCP602, which should give rail-to-rail output.

enter image description here

Using the same MCP602 op-amp as a comparator, I still get an output of only 3.71V. Swaping the op-amp for a LM358 unit, I still get a maximum output voltage of about 3.70V.

What could be the problem? Is it possible that all the op-amps I purchased are all faulty?

\$\endgroup\$
4
  • 5
    \$\begingroup\$ Where did you get the 'MCP602' from? \$\endgroup\$
    – Bruce Abbott
    May 16, 2021 at 5:25
  • \$\begingroup\$ Yeah, but the MCP602 doesn't have rail-to-rail input. See Vcmr in its datasheet. You might have better luck with a non-inverting configuration for this application. \$\endgroup\$
    – Ste Kulov
    May 16, 2021 at 5:54
  • \$\begingroup\$ @SteKulov But that is an inverting op-amp circuit so both inputs always have 2.5V - well within common mode input range. However the non-inverting config you suggest is subject to limited common mode range. \$\endgroup\$
    – Justme
    May 16, 2021 at 11:39
  • \$\begingroup\$ @Justme Ah, true. My bad. \$\endgroup\$
    – Ste Kulov
    May 17, 2021 at 1:48

1 Answer 1

Reset to default
12
\$\begingroup\$

I tested your circuit with an a genuine MCP602 (purchased from Element14) and an LM358. With Vin grounded the MCP602's output was 4.99 V, and the LM358 was 3.72 V. With Vin connected to +5 V the MCP602's output was 0 V, and the LM358 was 0.52 V.

Conclusion:- your 'MCP602' is a fake.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

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