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.

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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?

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    \$\begingroup\$ Where did you get the 'MCP602' from? \$\endgroup\$ 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


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.


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