how this H-brigde is working?

Discussion in 'General Electronics Chat' started by wiki., Sep 28, 2012.

  1. wiki.

    Thread Starter New Member

    Sep 28, 2012
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    Please help me out to understand how this H-brigde is working?
    i tried but i couldn't make any sense.
    i mean i know the general working of the circuit...but i don't know the reasons why one transistor goes to Saturation and other goes to cuttoff...

    i found it through google.it is attached in the form of image..
    thanks [​IMG]
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    It is a very simple circuit.
    When Q5 is turned off then R1 turns on Q1 and turns off Q2.
    When Q5 is turned on then it turns off Q1 and turns on Q2.

    Now you figure out the other side yourself.

    Don't you know how transistors turn on or turn off?
     
  3. wiki.

    Thread Starter New Member

    Sep 28, 2012
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    0
    Thanks For the Reply..
    but i still have some confusion!!
    why Q2 turns ON when Input A is High??
    i mean how are you finding out that Veb>=0.7V for Q2???
     
  4. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    When input A is high, and input B is low ...

    Q5 is on which sets the base of Q1 and Q2 low.

    Q1 is a NPN so it is off with a low at its base
    Q2 is a PNP so it is on with a low at its base

    Remember that on the other side of the bridge you have the opposite situation with input B low and Q6 off whcih sets the base of Q3 and Q4 high.

    Q4 is a NPN so it is on with a high at its base
    Q3 is a PNP so it is off with a high at its base

    Now, looking back at Q2 which was your question ...

    Its a PNP with its emitter at ground, its base pulled low, and its emitter pulled up to a higher voltage through the motor and Q4. Now do you see how Q2 is turned on?
     
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  5. Audioguru

    New Member

    Dec 20, 2007
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    No.
    The collector of Q2 is at ground. When its base goes low then its emitter also goes low like you said earlier.
     
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  6. JMac3108

    Active Member

    Aug 16, 2010
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    Oops, thanks for the correction!
     
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  7. wiki.

    Thread Starter New Member

    Sep 28, 2012
    4
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    JMac3108 and Audioguru i am very thankful to you...
    you have cleared my confusions. :D

    the concept of "Pulling" was new to me.i heard about pulling but i didn't understood it that time.... now i am somewhat clear about this concept. :)
     
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