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I am designing a phase-cut dimming driver for Incandescent bulbs as well as LED panel lights with dimmable drivers. Using a BTA24 Triac and VOT8121AB Optocoupler driven by my MCU.

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For zero-cross detect I am using a PC814 bi directional optocoupler enter image description here

My code looks right, it is based on my study of various articles and sample codes. It has been working with fans. The problem i am facing with is the lights, during light dimming i am seeing frequent flicks (The light turns off for few milliseconds).

I wanted to understand if this is the right circuit for phase-cut dimming driver or not. Should i be changing my design or values of capacitor etc. Is there an alternate design that can be used for proven better results?

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    \$\begingroup\$ Can you capture any glitches on the output from your MCU? \$\endgroup\$
    – winny
    Commented Nov 1, 2021 at 7:59
  • \$\begingroup\$ First of all you'd better to split 330k resistor in two lower values and arange them on both input traces. Instead of using a cap, use a schmitt trigger. The rest is not very described, but a 24A triac would have a large holding current, so it may be cause if the load current is small. There is also a phase lag I vs. V, so you have to keep the triac gate trigger high enough time after the ZC to start conduct in next half period. \$\endgroup\$
    – Marko Buršič
    Commented Nov 1, 2021 at 13:35
  • \$\begingroup\$ @MarkoBuršič. Makes sense. Understood. \$\endgroup\$
    – Daga Arihant
    Commented Nov 2, 2021 at 5:10

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You are using a BTA24 for phase cutting which means you can only do leading-edge dimming (turning on TRIAC up to next zero-cross pulse).

There may be two reasons to get flickering:

  1. If the controller is not able to read each and every zero cross pulse, and it won't turn on the TRIAC when it misses the zero-cross pulse (need to check each pulse using an oscilloscope).
  2. The flicker may appear if you don't use a proper dimmable LED driver at yje end side.

You mentioned the code is working with fans, but you can't figure it out properly with fan speed and if you operate the fan at below 40% it produces humming sounds in the long run (personal experience).

To solve the flicker issue you can try different dimming methods (trailing and leading edge) using MOSFET or any IGBT.

https://easyeda.com/TamojitSaha/fl5150_dimmer may useful for proper dimming with out reading zero cross.

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