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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

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  • \$\begingroup\$ Have you considered using a MOSFET to drive the motor with PWM? \$\endgroup\$
    – Bort
    Commented 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
    Commented 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
    Commented 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
    Commented Jan 31, 2018 at 22:21
  • \$\begingroup\$ Is there a long pause between moving? (I am thinking of a PTC) \$\endgroup\$
    – Oldfart
    Commented Jan 31, 2018 at 22:23

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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.

schematic

simulate this circuit – Schematic created using CircuitLab

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

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