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I have a 5 V water pump and a 5 V/2.4 A power source. These work together. Now I want to control it with a PWM signal from an STM32 board using a FQP30N06L N-Channel MOSFET and that doesn't work - nothing happens, the PWM signal goes out but the pump doesn't seem to get the power and doesn't turn on.

This is my circuit:

Schematic of the circuit

The diode looks dumb but it's the only one I could find rated over 2 A.

I would very much appreciate help in finding the error.

Photo of the perfboard with the circuit

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    – SamGibson ♦
    Commented Jan 13, 2022 at 9:18

1 Answer 1

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The issue was that the signal (the gate-source voltage) was too low for the MOSFET to open up with this load. With 3.3V it didn't open at all, with 5V it opened a little bit (and heated up a lot), and only with around 9V it opened fully. This is probably because this MOSFET is counterfeit and out of spec - here's a tweet with more info by someone who had a similar issue: https://twitter.com/ExtElec/status/1494060721818198020

Thank you everyone for the help!

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