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I am using this Triac circuit to control the brightness of several incandescent lights. The circuit monitors the phase of the 120 volt wall current, then signals an Arduino when the phase crossed zero. Based on this signal input, the Arduino switches the AC current which goes to the lights, limiting the amount of power that is feed to the lights. More info can be found here

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I read that this circuit can not be use to switch LED lights. Why is this? I am assuming it's because the switching rate is around 60 herts, which will cause a visual flicker. If so, can I connect the MoC3052-M input to a PWM output? This should switch the AC current fast enough to create an effective dimming effect. Will I need to alter the circuit in order to do this effectively and safely?

Here are my options for powering the LED's:

1) bridge rectifier only, powering the LEDs with 120 volts DC. 2) Wall Plug transformer (wall wart) to power the LEDs with 12 volts DC.

If there is another option to convert 120v to 12v or 9v DC, one that will work well with this circuit, please let me know.

EDIT======================

I plan to use this device for the switching:

enter image description here

The goal for this question is to find a way to use this device to dim an LED rope light (as well as the incandescent lights.)

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    \$\begingroup\$ Your 120VAC to 12VDC psu wont like being turned on and off repeatedly. Is there any reason you dont want to PWM the 12VDC side of the PSU? Its easier and safer. \$\endgroup\$ – Wesley Lee Jun 4 '16 at 1:53
  • \$\begingroup\$ Since your "120v AC to 12v DC converter" is a complete unknown, there is no way to predict how well it will tolerate phase-chopping "dimmer" control. If you live in 120V territories, then you probably have 60 Hz mains power which will flicker at 120Hz (or 60Hz at worst). Not clear where you got 33 Hz? \$\endgroup\$ – Richard Crowley Jun 4 '16 at 2:24
  • \$\begingroup\$ If the LED rope light uses a bridge rectifier, would it work? \$\endgroup\$ – Hoytman Jun 4 '16 at 2:49
  • \$\begingroup\$ yeah, as long as there is enough load to allow the triac to latch \$\endgroup\$ – Daniel Jun 4 '16 at 3:01
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    \$\begingroup\$ This is simply not answerable without details of the LED driver circuit, but as a general assumption it will most likely not work. Even trying it is not recommended as you do not know how it might fail. \$\endgroup\$ – Chris Stratton Jun 4 '16 at 4:05
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Certain types of LED light strings will work with AC Phase Control dimming - but most will not work.

What will most likely work is the series strings of LED Christmas Lights. These are simple series strings of LEDs with sufficient series resistance to keep the current at the proper level when fed with the rated AC voltage. The strings of this type that I have seen are actually two strings connected in inverse-parallel - one string conducts on one AC half-cycle, the remaining string conducts on the other AC half-cycle.

However, most LED lighting uses some form of Switch Mode power supply. Unless the power supply is specifically designed to work with AC Phase Control dimming, they most often do NOT work properly.

Like the comments say - how well this will work is completely dependant on how the LED string is designed and constructed.

Take one apart and see how it is built. Add your findings to your question and we can offer an opinion as to how well it might or might not work.

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  • \$\begingroup\$ one contains (only) a bridge rectifier. \$\endgroup\$ – Hoytman Jun 4 '16 at 7:32
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If you LED strip has only diode bridge rectifier + cap, and it has a low voltage AC input, then it will work. If the LED strip is more sophisticated using buck converter, then I guess it won't work.

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