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Need help to understand this circuit

  1. Oct 23, 2009 #1
    this is the circuit of JDM programmer.
    I'm trying to understand how Q2 works here.coz only base of Q2 get a voltage and emitter or collector is not connected to power supply,

    there is a description about this circuit,but I cant understand that description.

    here is the circuit

    http://img17.imageshack.us/img17/322/newpic22.gif [Broken]

    and this is the description

    Attached Files:

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 23, 2009 #2


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    The Micro being programmed can supply voltage or connect the RB7 port of the chip to ground.

    The connections at the right hand side of the diagram refer to a serial RS232 port on a computer which can also supply power.

    So, the transistor Q2 gets its voltages from these sources and it operates sometimes as a common base amplifier and sometimes as an emitter follower, which is a neat trick.

    You would have to know the programming software to work out the exact processses involved, but the description seems to describe the function of this transistor adequately.
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