I have created a circuit which implements PWM dimming using phase cutting with Zero cross detection which works well on incandescent bulbs but creates humming noise when connected to a fan. I am using BTA16-800CW (Snubberless triac) to control AC and my triac driver is MOC3023. The ZCD is done using SFH620A-3 opto coupler. I have not connected any snubber / rc filters as BTA16 is mentioned to have it inbuilt. Is the humming expected when doing PWM dimming ? Is there any way to get rid of it ?

I am using the standard approach to detect zero cross as shown below. enter image description here

  • \$\begingroup\$ Sounds normal. Where is your inductor? \$\endgroup\$ – winny Feb 26 '18 at 20:27
  • \$\begingroup\$ Not much you can do about it as you are driving the rotor with 60hz yet its back emf is not. This is why VFDs are used with AC motors. You will get a beat frequency between the rotor and the 60Hz drive. \$\endgroup\$ – lakeweb Feb 26 '18 at 20:32
  • \$\begingroup\$ Not directly related (hence the comment) but when I implemented some PWM on computer fans (12V, DC) I got humming when the PWM was done in an audible frequency. This suggests that unless you can switch the fan (A) Differently or (B) faster, you're going to get a hum. \$\endgroup\$ – Helpful Feb 26 '18 at 23:11

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