Do Triggering a half SCR half diode rectifier need Pulse Transformer?

Discussion in 'General Electronics Chat' started by whywhy68, Jul 9, 2008.

  1. whywhy68

    Thread Starter Member

    Jun 11, 2008
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    http://www.allaboutcircuits.com/vol_3/chpt_7/5.html


    As shown here a SCR rectifier need a pulse transformer to trigger SCR2 & SCR4 together.. but if suppose SCR2 & SCR1 is changed to a diode. Do i need a pulse transformer to trigger them?

    My circuit is as shown below..

    [​IMG]
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I have successfully done it like this. You have to pick component values depending on your application and SCR specifications.
     
  3. theamber

    Active Member

    Jun 13, 2008
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    But you will have to control the triggering of the diodes manually. By applying the required voltage to turn them on.
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    What does this mean? The trigger timing can be in a feedback loop. I wouldn't consider this to be manual control. Did I misinterpret your meaning?
     
  5. theamber

    Active Member

    Jun 13, 2008
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    No disregard my post I did not read the link. I thought you wanted to use a triggering mechanism without the scrs.
     
  6. whywhy68

    Thread Starter Member

    Jun 11, 2008
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    [​IMG]


    1) May I know what is R3 used for?

    2) Is R3 included in controlling the firing angle of the SCR ?

    3) May I know what is the related formula for adjusting the firing angle of the SCR with C , R2 ,R3(if needed) ?


    Would greatly appreciate if some expert can assist me over here. I am using the SCR for making a AC/DC rectifier
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    R3 is a bias for the SCR, and yes, it is definately part of the phase shifter. I'll let someone else take question #3.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    R3 keeps the SCR off when it is not triggered, by providing a path to ground for the gate current. It may need to be a lower value, depending on the SCRs you choose. The trigger signal must be a fast-rising positive pulse edge, so R3 has no effect on the phase. The same is true of C1, R1, and R2.
    The circuit below is one way of controlling the phase. You may find a simpler way to do it.
     
  9. jpanhalt

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    Jan 18, 2008
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