Rectified wave problem


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  1. #1
    Join Date
    Dec 2012
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    Türkiye
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    Default Rectified wave problem

    Hi everyone;

    I'm upto a triac control circuit . So , in order to control the triac triggering angle we need to detect the zero crossing points .. I've made the attached circuit schematic on a breadboard but I'm having too weird problem about the full wave rectified sine wave .. The rectified wave can not reach to zero cross twice but only once during a period and plots an unintended line as seen on the attached picture .. I've changed the circuit components for a thousands of times including the resistors , capacitors , bridge rectifiers , transistors even the breadboard ... The rectified wave even acts same on a single load resistor ...

    What could the problem be ?

    PLEASE HELP ... Name:  Zero cross detector.jpg
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    Last edited by gunayburak; - 15th July 2014 at 01:18.

  2. #2
    Join Date
    May 2013
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    australia
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    Default Re: Rectified wave problem

    looks like your ac signal earth reference is biased one forward diode voltage above earth.
    you need something like this
    Attached Images Attached Images  

  3. #3

    Default Re: Rectified wave problem

    I use 'ac opto' to get 0xing. vary R3 to change width of the zero areaName:  zero xing.JPG
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    oh, add series resister to opto input !!

  4. #4
    Join Date
    Dec 2012
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    Türkiye
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    103

    Default Re: Rectified wave problem

    Quote Originally Posted by amgen View Post
    I use 'ac opto' to get 0xing. vary R3 to change width of the zero areaAttachment 7388

    oh, add series resister to opto input !!
    Thanks for your replies guys .

    To amgen ; Why would we still need the diodes and the cap since the AC opto and a series resistor are sufficient to detect the zero crosses ?
    I mean the following link would have sufficied I suppose ?

    http://i.stack.imgur.com/sw3mO.png

  5. #5

    Default Re: Rectified wave problem

    thought that was part of your power supply stuff !! otherwise then not needed.
    don

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