Need help

Discussion in 'Homework Help' started by ambadi, Jan 31, 2012.

  1. ambadi

    Thread Starter New Member

    Jan 31, 2012
    1
    0
    what is the use of a capacitor and a resistor in series and a diode in between them with diode's positive connected to ground?

    in the circuit attached it is before the amplifier section with pn2222a
     
  2. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    C5 and R5 form a differentiation circuit that turns the positive going square wave edges into short pulses that turn on the flyback transistor for short periods of time. D1 provides a discharge path for C5 when the square wave goes negative.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The reason for restricting the excursion of the negative-going spike at the base of the transistor as noted by jimkeith is that if the amplitude of the negative-going spike is significant, it can damage the transistor. So the diode is there as a protective measure against damage to the transistor's base-emitter junction.

    hgmjr
     
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