I have a situation where a small DC motor is moving the flap from one side to the other. The flap can be in two positions but without limit switch. Change of position lasts about 3 seconds. The problem occurs when the motor reaches its position, but still has supply. After some time it can easily break gears. So I want to limit the current for the motor in at least one direction.

I have been thinking about this simple current limiter, but is it a problem when it gets reversed supply? Is it ok to solve it with one diode which will conduct most of the current in that situation?

enter image description here

  • \$\begingroup\$ Have you considered using a MOSFET to drive the motor with PWM? \$\endgroup\$
    – Bort
    Jan 31, 2018 at 21:50
  • \$\begingroup\$ I want to keep it simple and I can not change electronics that drives the motor. \$\endgroup\$
    – Lazaro
    Jan 31, 2018 at 21:53
  • \$\begingroup\$ Just to be sure: does the motor turn/run one way only or two ways? In the latter case you can not use the above circuit. \$\endgroup\$
    – Oldfart
    Jan 31, 2018 at 22:17
  • \$\begingroup\$ It turns in two ways. Is there some other solution? With two LM317 as current limiter, and two diodes maybe? \$\endgroup\$
    – Lazaro
    Jan 31, 2018 at 22:21
  • \$\begingroup\$ Is there a long pause between moving? (I am thinking of a PTC) \$\endgroup\$
    – Oldfart
    Jan 31, 2018 at 22:23

1 Answer 1


Sorry it is now past 1 AM here and I am getting tired. I just wanted to give you a heads-up what the idea was. The bridge rectifier makes sure that the current through the circuit always goes the same way, no matter which way the motor turns.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Thank you, I didn't consider that a bridge rectifier can be used like this. This could be the solution. \$\endgroup\$
    – Lazaro
    Jan 31, 2018 at 23:03
  • \$\begingroup\$ What is D5 for? \$\endgroup\$
    – topher217
    Oct 2, 2020 at 7:41

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