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Topic: RobotDyn AC Light Dimmer and Transformer Operation (Read 181 times) previous topic - next topic


Building a larger scale foam cutter 110V AC power supply and attempting to replace the conventional Lutron Dimmer switch with an Arduino driven system.  I'm using the RobotDyn Controller


It works great as a light dimmer but when I use it with a transformer I get a buzz.  My research has found that the problem may be because of leading edge/trailing edge issues.  Wondering if anybody out there has faced this issue and have any solutions to offer.



Transformers are designed for a sine wave and nothing else, unless it is a pulse transformer. But in your case, does the buzz hurt anything or is it just annoying? Does the transformer get hotter than normal?

There should be no problem in doing what you are attempting, unless the above is a problem.



Looks like "cutoffs introduce an extra high frequency component to the waveform" according to an answer I got on Amazon.  I'll do some more testing (see what it looks like on my scope) and see if I can live with the noise.  Any suggestions on another Arduino driven option?



Excellent tutorial on AC power at: http://www.bristolwatch.com/arduino/arduino1.htm.

Installed the snubber he describes (1K resister and 0.1uF capacitor) between the output power and neutral lines.  Buzz was eliminated up to 90% power and much less than before at higher power settings.  I'll experiment with different resistor settings to see if I can improve the results.


Aug 27, 2019, 02:29 am Last Edit: Aug 27, 2019, 03:02 am by WattsThat
Just to clarify, a snubber is not connected hot to neutral, it across the triac terminals MT1 and 2. It's there to help the triac behave properly with an inductive load.

The schematic is correct, just poorly drawn which may be the source of your confusion.

st.com triac app note an437
Vacuum tube guy in a solid state world


Personally wondering if instead of trying to "dim" the output by "cutting" the waveform, just use the zero cross portion of the robotdyn to "pulse" the output for full or 1/2 cycles.

Your transformer will receive a smooth signal so no unusual noises or wasted heat or additional circuitry needed?

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