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I have a problem with my permanent magnet DC brushed motor. I'm trying to drive it from N-Channel and P-Channel MOSFETs from STM32F100 pin (3,3V logic). I want to turn the motor on and off only, speed is controlled via step-down converter (LM2679-ADJ) and potentiometer. At first I tried to turn the motor on by push button connected to STM pin. Every time the motor has stopped after half of a turn (it has mechanical commutator). Both transistors turned off without my input. Later on I've put instruction in main loop of STM to constantly turn on the N-MOSFET and the motor started to work properly. I wonder what is wrong in schematics that causing that particular situation. I measured voltage across Zener diode and it's 12V when N-MOSFET is turned on. IRF5210 is fully turned on at Vgs=-10V according to datasheet.

Schematics in attachment. Any help will be appreciated.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

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    \$\begingroup\$ @WesleyLee You are fast as a weasel! rayvburn, please use the schematic editor. \$\endgroup\$
    – winny
    Commented Oct 30, 2017 at 19:55
  • \$\begingroup\$ Also, please measure gate-source voltage. 10k pull down sounds like a very high value. Not unreasonable, but high. \$\endgroup\$
    – winny
    Commented Oct 30, 2017 at 19:57
  • \$\begingroup\$ "Later on I've put instruction in main loop of STM to constantly turn on the N-MOSFET and the motor started to work properly." So your schematic/hardware works fine.. \$\endgroup\$
    – Trevor_G
    Commented Oct 30, 2017 at 20:11
  • \$\begingroup\$ Vgs seems to be right - stays at 3,3V (just like STM's supply voltage) when the N-MOSFET is on. \$\endgroup\$
    – rayvburn
    Commented Oct 30, 2017 at 20:43

2 Answers 2

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Later on I've put instruction in main loop of STM to constantly turn on the N-MOSFET and the motor started to work properly.

Then the hardware is obviously working, and you have a software problem.

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  • \$\begingroup\$ The point is - once the N-MOSFET is turned on I want it to stay turned on till the moment I push another push button and turn it off. Now, I have to constatly re-set the pin state to high to achieve continuous turning of the motor. \$\endgroup\$
    – rayvburn
    Commented Oct 30, 2017 at 20:21
  • \$\begingroup\$ @rayvburn then your micro may be resetting or you have a bug in the firmware. YOu may have bad grounding or not enough caps on the power lines though to trip the reset. \$\endgroup\$
    – Trevor_G
    Commented Oct 30, 2017 at 22:11
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It was a software problem. Noises from brushes caused executing interrupt routines from the button which turned off transistors. 470nF ceramic capacitor between motor inputs and 100nF between button legs solved the problem.

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  • \$\begingroup\$ You can accept this answer - even if it is your own - to signify the solution. \$\endgroup\$
    – Transistor
    Commented Nov 4, 2017 at 10:43

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