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I want to PWM lights with Arduino and IRF3205 N-channel MOSFET.

For fully turning the MOSFET on I am using this circuit. The op amp (datasheet here) and load are powered by a single 12V source (lead acid battery).

Circuit

(MOSFET has 100k pulldown resistor at gate, not shown in circuit)

Now the output stays high even when I manually connect inverting input to +12V and non-inverting input to ground. I tried three ICs and they are not damaged so it is not the IC. It is so frustrating.

Only way that the MOSFET turns off is when I short gate and source together. Then it turns on slowly during 1 sec and stays on until I short those pins again.

The MOSFET turns off after the IC is removed from the IC socket.

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    \$\begingroup\$ Show all power rails. Show that mosfet source ground point connects to op-amp ground. Link to a data sheet for the op-amp. \$\endgroup\$
    – Andy aka
    Commented Aug 15, 2019 at 12:01
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    \$\begingroup\$ They ask you for a complete schematic because words are too easy to misunderstand when discussing circuits. \$\endgroup\$
    – JRE
    Commented Aug 15, 2019 at 12:54
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    \$\begingroup\$ SE provides you with a circuit designer that you can used from any browser. \$\endgroup\$
    – Scott Seidman
    Commented Aug 15, 2019 at 13:00
  • \$\begingroup\$ The link to the datasheet needs to be edited into the post, not posted as a comment. I've edited it in. \$\endgroup\$
    – Null ♦
    Commented Aug 15, 2019 at 14:05
  • \$\begingroup\$ If the MOSFET has a pull-down resistor on the gate, that should be shown on the schematic - the note in your question could easily be missed by someone viewing the schematic. The schematic must be an accurate representation of your circuit. \$\endgroup\$
    – Peter Bennett
    Commented Aug 15, 2019 at 16:01

1 Answer 1

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Your negative image is hard to see. The opamp has no pin numbers.

Is the opamp a fake LM358 from ebay? Or did you connect the opamp pins backwards?

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