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Original question:

LM358: LM358 comparator transition issue

LM358: LM358 Transition issue from -5V DC to +5V DC at the Output Pin of comparator

Ramana Murthy
Expert 1765 points
Part Number: LM358
Other Parts Discussed in Thread: LM393

Dear Sir,

LM358 Transition issue from -5V DC to +5V DC at the Output Pin of comparator

Voltages at Pin 2 is higher than Pin 3 Still Output is Positive.
Please resolve my problem.

I tried with LM358 (SMD Package) and LM393 (SMD Package), But not getting proper output.

Please find the voltages at every pin of op-amp LM358
Please find the attached Schematic and suggest the changes.

1651.LM358.pdf

Regards
Murthy

  • 0
    TI__Genius 15410 points

    Hi Murthy,

    Both input pins (Pin 2 and 3) are outside the common mode voltage range (2V below Vcc = 3V). Therefore, it is possible to see phase inversion. I recommend reading Section 9.3.3 of the datasheet and also "Design Guidelines for Devices with LM324/LM358 Cores" for more information.

    You will need to reduce the input voltage to one of the input pins to remain within the Vcm range of the device (2V below Vcc) as recommended in the datasheet and app note for proper operation. If you cannot reduce the input voltage to the pin, I suggest finding another device with a rail to rail input. To find the best device, I suggest creating a new forum post about the LM393 and our comparator team will help you out.

    Thank you,

    Tim Claycomb