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Circuit diagram to analyze that looks wrong to me

  1. May 22, 2008 #1
    I have a circuit diagram to analyze that looks wrong to me. It is fairly straight forward and I will attempt to describe it. It is an unlabelled power source with the neg terminal feeding a photocell, that part I understand. Here is the problem, that same neg branch of the circuit also feeds into the collector terminal of an NPN transistor with the base terminal of the NPN transistor receiving the switched neg fom the photodiode. It appears the intention of the design was to use the photodiode to switch the transistor which switches a light. Kind of like how the steet lights come on at dark. My question is, can an NPN transistor function with this bias, neg to collector, switched neg to base and pos side of light bulb connected to emmitter?
     
  2. jcsd
  3. May 22, 2008 #2

    NoTime

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    What are the two classes of bi-polar transistor?
     
  4. May 22, 2008 #3
    NPN and PNP
     
  5. May 22, 2008 #4

    NoTime

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    Ok, which one is your project using?
     
  6. May 22, 2008 #5
    npn by the symbol
     
  7. May 22, 2008 #6

    NoTime

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    From your description this doesn't sound correct.
    Perhaps you should post the schematic.
     
  8. May 22, 2008 #7
    circuit diagram
     

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  9. May 22, 2008 #8

    berkeman

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    Circuit looks wrong, or it's a trick question (like the answer is "never").

    The load should be directly connected to the collector, and the voltage source should have + on top of the load, and - down on the emitter. The cathode of the photodiode should also connect above the load to the + supply.
     
  10. May 22, 2008 #9

    NoTime

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    In this case it looks like the battery symbol is backwards.
    The same issue applies to the photodiode as well as the transistor.

    Edit: You beat me to it B, I considered the "never" answer as well :smile:
     
    Last edited: May 22, 2008
  11. May 22, 2008 #10
    Thanks to all that took the time to have a look at this thing. My text is full of misprints and omissions.
     
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