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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
    http://www.jdm.homepage.dk/newpic7.htm"
     

    Attached Files:

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

    vk6kro

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    Science Advisor

    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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