how to solve this distortion from output rectifier?

Discussion in 'General Electronics Chat' started by skychan1213, Nov 13, 2008.

  1. skychan1213

    Thread Starter New Member

    Jul 10, 2008
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    hello everyone..i am doing my final year project, and my project title is semicoductor tap changer for power transformer.as shown in the picture, the output from the full wave reticfier is distorted.what action i should take to solve this problem?thank you very much....from: ching shi
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Looks like a perfectly good full wave rectifier output to me....what's the problem?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    I think he's talking about the "flat spot" around the zero crossing caused by the Vf of the diodes in the bridge rectifier.

    If you want to get away from that "flat spot", you could either use a synchronous rectifier circuit (uses power MOSFETs as "ideal diodes") or a precision rectification circuit.

    Some ideas: http://en.wikipedia.org/wiki/Precision_rectifier
    Precision FW rectification circuit on EDN: http://www.edn.com/contents/images/6250014.pdf
    Another article on precision rectification: http://www.arrl.org/tis/info/pdf/0707053.pdf
    (but it uses 741 opamps - I'd use something better, like an LF353, TL072 or perhaps an LT1057)
    A paper on synchronous rectification: http://scholar.lib.vt.edu/theses/available/etd-173510281975580/unrestricted/chapter2.pdf
    Google search: http://www.google.com/search?hl=en&q=precision+rectifier+circuit (84,000 hits)
     
    Last edited: Nov 13, 2008
  4. Wendy

    Moderator

    Mar 24, 2008
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    It still won't be perfect, bu their is also Schottkey Diodes. They drop a less forward voltage.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    BAT54's have among the lowest Vf, if you don't pass much current through them. 100uA will give a max Vf of around 240mV. Basically, the less current through, the lower the Vf. If our OP substituted BAT54's for his bridge, the "flat spot" would narrow considerably, but wouldn't go away completely.
     
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