Bistable Thyristor

Discussion in 'Homework Help' started by Steve1992, Oct 28, 2006.

  1. Steve1992

    Thread Starter Senior Member

    Apr 7, 2006
    100
    0
    Hi,

    Im confused on why both SCRs dont turn on at the same time?

    Is this because, C2, initially acts as a s/c, so Q1 will turn on first?
    C2 would therefore determine the lamp switching on/off frequency?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    C1 determines the switching. It looks as if Q1 will turn on first. As it conducts, the Q1 side of C1 goes to ground, while the Q2 side charges up to 12 volts. The next pulse hits both scr's, but only Q2 is properly biased. Q1 has 0 volts across it. It is still conducting because of the current through it and the lamp filament. So Q2 turns on and pulls enough charge off C1 that the voltage across Q1 reverses, and Q1 drops out of conduction.

    The charge across C1 settles down in the opposite direction, so the next puls will Turn on Q1 and turn off Q2.
     
  3. Steve1992

    Thread Starter Senior Member

    Apr 7, 2006
    100
    0
    I believe C1 is acting as a commutation capacitor.

    Am I right about C2 being there to ensure Q1 switches on first, becuase
    an uncharged capacitor acts as a s/c initially?

    What you wrote, sounds good to me.

    Thanks.
     
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