I live in Ireland, on a 240V/50Hz supply. I run a Wink Hub, and therefore am bound to using US based Z-Wave frequencies, which usually operate on a 120V/60Hz supply.

I have an Aeon Labs Dimming Module, and have checked the components for suitability for 240V. The TRIAC is rated 600V. I have tested this on an incandescent lamp, and it operates fine; however, I am yet to test this on a LED luminaire to see if it flickers. I have been told a dimming device created for one regional frequency could flicker on another frequency (a 60Hz dimmer on a 50Hz supply).

My question is concerning the technical operation of the dimming feature. I can see it uses a TRIAC. The Z-Wave ZW0301 chip has a ZEROX pin (zero-crossing).

Once it has synchronised with a zero-crossing, it is my understanding that it waits a period of time before switching on the TRIAC until the next zero-crossing (known as leading-edge dimming). The amount of delay would be a function of the period/frequency, and the amount of dimming required. If the device was programmed for 60Hz, and was operating on a 50Hz supply - all I can fathom happening is that it would not have the same 'range' of dimming.

Why wouldn't a manufacturer simply use the zero-crossing to synchronise/determine the exact frequency of the line it is operating on; instead of hard-coding the device to either a 60Hz or 50Hz value?

So - the only issue I can see with flickering on LED luminaires would be due to the LED driver itself not drawing enough via its bleeder circuit to latch the TRIAC once it has fired. Which has nothing to do with 50/60Hz.

So when a manufacturer says 'compatible with most leading and trailing edge dimmers', I can only assume it is to do with the choice of L and C used on the dimmer - and whether or not the LED driver has an appropriately sized bleeder. Adding a few more LED drivers on the same line would probably resolve any of those issues though.

Any thoughts on my ramblings?


1 Answer 1


I have now worked on several products that incorporated triac controls. Cost was the driving force when selecting their features and functions. The cheaper product's microcontroller simply did not have enough memory to support dynamically selecting 50/60. Therefore the software was hard coded and two market specific software versions were made.

The more expensive product needed a micro with more inputs and outputs. This gave the micro the side effective of having more memory. The greater memory gave the ability to code dynamic 50/60 support.

Triac's have a minimum on pulse value to ensure that they turn on. The software that I have dealt with slides that pulse around to change the dimming. The problem can come from how often that pulse is synchronized with the zero crossing. If it's every half cycle then the wave form is symetric and there won't be any problems until very low dimming is needed. In the scenario the pulse will slide over top of the trailing zero crossing false triggering the triac for another half cycle. This would cause flickering but only when a very low dimming state is reached.

If the synchronization happens every cycle then the waveform won't be symmetric between the first half cycle and second half cycle. This will cause flickering as soon as dimming is induced.

  • \$\begingroup\$ Doesn't the TRIAC automatically turn itself off at a zero-crossing? And doesn't a TRIAC turn on with a simple pulse to the gate pin? So, once a zero crossing occurs, it delays an amount of time, and then pulses the TRIAC gate causing it to 'latch' on (or 'fire' I think I've read). It stays on until it reaches a zero-crossing, and stays off until another pulse occurs on the gate to latch in on again. So wouldn't the uC need to know about this zero-crossing to start its delay timer? \$\endgroup\$
    – mriksman
    Commented Jan 7, 2016 at 12:45
  • 1
    \$\begingroup\$ @mriksman Correct, you described the first scenario i listed. The second scenario times two pulses of a single zero crossing. \$\endgroup\$
    – vini_i
    Commented Jan 7, 2016 at 12:57

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