Mosfet circuit to drive 12V 2A DC motor

  • I am going to put together an external driver for a 12V 2A motor driven from a PWM fan output. I see the PMV40UN2 is rated for 4.4A max but I assume the traces, connector, or cooling are not up to that based on the documentation max of 1.5A for the fan outputs. My question is would there be any disadvantage to using a dirt simple circuit or using a NPN / PNP pair between the fan output and the IRLB3034 mosfet I plan to use. (The reason for the 3034 N channel is that I have several of them in my parts stash) Also, do any of you more advanced electrical people see a problem with either of the circuits I threw together? I'm not an engineer but have played with electronics all my life.

    EDIT: Perhaps the 1.5A limit would not apply if I used an external +12V if the limit is due to the positive side of the board wiring?

  • administrators

    Does your motor really draw 2A continuously, or only when starting? If it's only when starting then you can drive it directly from the Fan0 output, using a flyback diode if your Duet is not the 1.02 revision.

  • No diodes anywhere near the fan outputs on the board, just the resistors. I just measured and 1.69A full load, 1.03A no load, and after doing about 30 starts measuring max instantaneous most were in the range of 1.89A to 2.12A although I did get a 2.63A and a 2.86A instant peak on 2 starts under load. If I go the direct route I'll put a fast blow fuse in line, a 2A 3AG would never blow under normal conditions.

  • administrators

    Sounds OK to drive it directly then. The version 1.02 Duet has flyback diodes for the fan outputs built in, the 1.0 and 1.01 boards don't.

  • Thanks

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