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diac troubles in a heater circuit

Discussion in 'General Electronics Discussion' started by tuneup, Jun 13, 2018.

  1. tuneup


    Jun 13, 2018
    I have a rather simple circuit that controls heating elements. After testing each component, I find them all good except the r20 (47 ohms resistor And the diac.( the diac show a few ohms in each direction when tested with an ohm meter). I have replaced the 47 ohm resistor but don't have an idea of what diac would work in this circuit.
    This is were my electronics stop and your help is needed.
    This diac is the only component that I can't identify. I will add a circuit diagram I found that is wired exactly the same.
    the component values are slightly different. they are:
    r20 = 47 ohms
    c24 = .224uf
    triac = 56026
    c23= .104uf
    r19 = 1k ohms
    vr4 = 0-500k ohms
    diac = unkown
    the load is a 240 volt heating element.
    thanks for any help.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    A typical diac has around 30 V to 40 V breaktrough voltage. In this circuit it is used to cerate a rising edge to trigger the triac. The absolute parameters of the diac are very likely not critical. Any off the shelf component should be usable.

    btw: a bit misleading is the text giving R20 = 47 Ω but the schematic showing R20 = 100 Ω
  3. tuneup


    Jun 13, 2018
    Thanks so much for the help and info. I ordered a db3 this morning.
    Sorry I wasn't more clear for the drawing, it is one I found on the internet that just happens to be exactly as my circuit except for the values of the components. that is why the components were stated out.
    thanks again.
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