SMPS Power supply: MP 3800

I have a 12V brushed DC motor hooked up to a PWM controller. When I run the motor (all works as it should) however there is a lot of crackling noise coming from the PSU.

Note: Snubber diode (or 'Flyback' diode) added due to PWM Controller manual recommendation.

Considering the PSU has its own PWM...am I creating dirty power by chopping the signal once again with my PWM controller?


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ You aren't doing anything terribly wrong, but your design really needs some capacitors between the PSU and the PWM controller. \$\endgroup\$
    – hekete
    Jul 26, 2019 at 6:08
  • \$\begingroup\$ @hekete - How many caps should I shunt and how best to calculate them? (Assuming electrolytic will be ok?) \$\endgroup\$
    – SheerKahn
    Jul 26, 2019 at 6:13
  • \$\begingroup\$ How much current does the motor draw? \$\endgroup\$ Jul 26, 2019 at 7:33
  • \$\begingroup\$ @BruceAbbott - 2-3A normal operation. 5A under stall conditions \$\endgroup\$
    – SheerKahn
    Jul 26, 2019 at 7:47
  • \$\begingroup\$ There are too many unknowns to really make a best calculation. You can either scope it, or go with the usual method of trial and error. A 100nF ceramic is usually a good place to start for noise. Then maybe try 10,47,100uF electrolytics and see if it improves at all. \$\endgroup\$
    – hekete
    Jul 27, 2019 at 4:04


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.