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Resistance power rating for this AC dimmer circuit?

Discussion in 'General Electronics Discussion' started by Laciecion, Nov 24, 2019.

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  1. Laciecion


    Nov 24, 2019
    Hi everyone!
    I was reading this really nice page about light dimmers when I saw this diagram for a AC dimmable led bulb dimmer and thought about giving it a try.[​IMG]
    It is build around a FL5150 IC, here you can find the datasheet. My question is about the power rating needed for the resitors and voltage rating for the capacitors, I have seen it using 1206 1/4W SMD resistors but I am not sure if that is safe enough.

    It would be nice if someone could help me to figure this out, hope this is not a stupid question I am getting started with electronics and learning a lot in this forum.

    Thank you!
    Last edited by a moderator: Nov 25, 2019
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    1/4 W power rating is probably o.k.
    Note that Rsense1 and Rsense2 need to be rated for 230 V AC or higher (at 2MΩ power dissipation will still be very low).
    You'll have to observe safe isoaltion gaps between different traces/wires at high differential voltages.

    This circuit is connected to dangerous live voltages on mains level. This is not a suitable circuit to get you started with electronics. I suggest you start with low voltage circuits, possibly battery powered or powred by a low power voltage source (e.g. a 5 V USB power supply from a charger).
    bertus likes this.
  3. bertus

    bertus Moderator

    Nov 8, 2019

    @Harald Kapp said, use a low voltage source.
    This is a solid advice.
    Direct mains powered equipment will be dangerous and can even be leathal.

    As for safety rules, you could have a look at the following page:



    May 20, 2017
    I will add my voice to those urging extreme caution which amounts to DON'T. As advised, start with something that requires no more that 5 to 15V dc.
    Cannonball and bertus like this.
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