TRIAC Circuit Element Confusion

Discussion in 'General Electronics Chat' started by BigHairyAnimal, Dec 23, 2016.

  1. BigHairyAnimal

    Thread Starter New Member

    Dec 23, 2016
    Hello AAC Universe,

    This is my first post on here so please forgive any manners that I've yet to learn. I'm in the middle of a power electronics project and have taken a respite to study phase shifting TRIAC circuits so I can use them in my new designs. I have a good grasp of the circuit design and how to snub things for motor control but keep coming across two things in standard off-the-shelf designs that I don't understand:

    1) The designs often show the capacitor between the gate and the anode instead of between the gate and the cathode. It's almost like they swap the capacitor and resistor locations. This complicates things in my mind. Why would they do this? Is it functionally different?

    2) A full-wave bridge rectifier keeps showing up in the designs and I can't figure out what it's for. Are they just using it as a diode array? Is it some kind of feedback system?

    The "off-the-shelf designs" I speak of are eBay purchases which often go by the name of "Dimmer Circuit" or "Power Regulator". I've included a photo of one such circuit as well as my hand-drawn reverse-engineered schematic of it. Help?
  2. ScottWang


    Aug 23, 2012
    The circuit looks like doesn't right, where is the AC110V input, why the 33K connected together, could you take a photo for another side of PCB and please check the circuit again.

    What is your new designs?
  3. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    Agree. the schematic doesn't look right.

    Also a Triac does not have an Anode and Cathode. They use MT1 and MT2; Look at the datasheet. The triacs have "trigger quadrants" and they are not quite equal in operation.
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    ScottWang likes this.
  5. BigHairyAnimal

    Thread Starter New Member

    Dec 23, 2016
    Thank you everyone! Dodgy - thank you for that perfect answer on the bridge. A clever circuit indeed.

    Everyone else, I've attached a photo of the bottom board traces. Also, in my hand drawn schematic: line hot comes in top left, output (and load) top right. Any thoughts on my first question?