Input Frequency for Triac Driver

Discussion in 'The Projects Forum' started by Gurmani, Dec 24, 2012.

  1. Gurmani

    Thread Starter New Member

    Dec 24, 2012
    Dear All.
    I am detailed to control a small single phase 220VAC 50Hz Motor by pulse width modulation circuit and using an optoisolator Triac Driver.
    I have designed a pulse width modulation circuit by using LM3900 Op Amp and MOC3083 Optoisolator (with zero crossing) for Triac driver.
    This circuit is malfunctioning as the motor is jumping and taking jerks in rotation.
    I think that frequency of pulse modulation circuit which is input of optoisolator is wrong.
    When I checked it by oscilloscope the frequency was about 1khz, then I adjusted it to 50hz but the problem is same.
    Can any body help me to advise the exact frequency of this circuit for triggering of Triac. Thanks
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    can you post a diagram, you may be triggering your triac with the wrong phase.
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    An AC motor can cleanly be controlled by essentially PWM of the 50//60hz AC line. An easy way to do this is with a capacitor and potentiometer - see nice write ups on Wikipedia or eBook on this site.

    If you need to use a uController, monitor a zero cross with the Controller and delay the trigger pulse to start the triac as needed.

    A 1000Hz control ow PWM will make harmonics with the 50 Hz and may cause jerkiness. As the motor is started in various times along the AC pulse. Remember, once a triac is triggered, it stays on until the AC mains cross zero, no matter what signal is on the triac trigger (control) pin.