Electronic – Controlling MOSFET and LED from same PWM output


I am controlling a MOSFET and LED from the same PWM output from a PIC. The MOSFET is driving a fan, while the LED is used as rough visual indicator of the speed. The circuit is below and it seems to work and I have not experienced any problems yet. But, I am unsure if this is recommended.

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Looking at the suggestions, I made the following changes.

  • added diode to fan
  • replaced R21 and with R22 and LED1

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Best Answer

The MOSFET takes no significant current from the output pin and the 2k2 in series with the LED will not pull the voltage down. Q2 should be a digital type (turn on 5V). The 10K could be lowered to discharge the gate-source charge more quickly and I would add a (snubber) diode across the fan just in case of spikes when it is turned off.

It works!