Triac Ringing?

Discussion in 'General Electronics Chat' started by wd8cxb, Sep 22, 2015.

  1. wd8cxb

    Thread Starter New Member

    Jul 8, 2009
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    upload_2015-9-22_13-8-42.png upload_2015-9-22_13-9-30.png upload_2015-9-22_13-13-16.png

    My Triac circuit that is controlling a motor load that has ringing when it turns on and off. Even when feeding a resistive load the ringing is present.

    I have a 0.33uF Snubbing circuit on the output of the triac. The input voltage is 230VAC and either 50Hz or 60Hz. The images below was on a 60Hz source. The circuit will be used on both 50Hz and 60Hz.

    I have read that the noise could be cause be the phase angle when I turn the triac on as well as not having a snubbing filter in the gate portion of the circuit.

    I am rather confused as to what is actually causing this "spike" or ringing. I have tried controlling the load a couple different ways. The first was maintain the turn on angle and then varying the pulse width and varying the phase angle based on the zero crossing.

    Both work but both have the ringing noise in the waveform.

    What can I do to correct this, change the firmware, add a filter on the input? Change the value on the Output cap? Change the value of the trigger resistor?

    I have played with all of the above thoughts but nothing seems to make a difference.


    This is the ringing shown as the triac is switching.
    upload_2015-9-22_13-8-42.png

    Here is a different view showing the input and output signal.

    upload_2015-9-22_13-9-30.png

    This is the circuit controlled by a PICF689
    upload_2015-9-22_13-13-16.png
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    One possibility is that the ringing is a scope, or scope probe artifact, and not really there or at least not so large. Beyond that, ringing is a resonance effect, and always involves both inductance and capacitance. A scope probe ground lead makes a dandy loop antenna (the inductor) feeding the probe's intrinsic capacitance. Other culprits are the load, its wiring, pc board traces, etc. Using all X and Y rated ceramic caps, move some with the shortest possible leads across various circuit elements. This might localize the source.

    1. ViewDraw (DxDesigner, Mentor Graphics, whatever)?

    2. TBDBITL?

    ak
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If your 230VAC input is mains-derived it will have noise on it.
     
  4. wd8cxb

    Thread Starter New Member

    Jul 8, 2009
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    I agree there would be noise on the mains but not like this. Still something to consider though.

    The unit currently is powered directly from the a 230V/60Hz outlet. If I run 50Hz it would come from a motor generator set.
     
  5. wd8cxb

    Thread Starter New Member

    Jul 8, 2009
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    I did try to move things around just in case. Also setup a ground plane under the circuit board using a sheet of aluminum conected to earth ground.

    I have tried a couple of different loads. It seems very odd. I did put a .1uF X2 Cap on the input and that make it a little better but not by much. Also tried a .68uF X2 Cap.


    Unfortunatley not part of TBDBITL. Went there many years ago and tried out but did not make it. Wanted to dot the I!!!!! Was only there for one year then transfered to BGSU so never got the chance again.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    The motor is inductive, so a spike or two here and there is inevitable on sharp switching edges. As others have mentioned; the ringing could also be an artefact of the scope lead.

    The triac datasheet should specify a figure for Dv/Dt, if edges are steeper than that, it can trigger the triac other than by the gate - if its causing a problem, you should be able to cure it by making the snubber "stiffer".
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    By move around I meant move the capacitor from one location to another, using it as a high frequency AC short to see if there was one particular component that was noisier than the others.

    ak
     
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  8. wd8cxb

    Thread Starter New Member

    Jul 8, 2009
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    I did not get a chance to work on this today but will try moving the cap around to different places. I did order some other capacitors to make the snubber a little more stiffer. Right now the snubber cap is a .33uF. I planned on changing it to a .68uF cap.

    I do appreciate all the ideas!!!

    Thanks!
     
  9. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Why is that ringing/spike important? is it causing you trouble in the control side of the circuit?
     
  10. umphrey

    Member

    Dec 1, 2012
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    I have had this problem many times! Are you using a differential probe? One thing to try is connecting a 2nd probe to the circuit, but connect both probe leads to the same point so you know that probe should read 0 voltage. It probably won't, but whatever it reads will give you an idea for how noisy your measurements are. Be careful with grounding if you aren't using differential probes!
     
  11. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    You can limit the spikes (if they're real) using a tvs diode of an appropriate value
     
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