Transistors

Discussion in 'Homework Help' started by domandrzejczuk, Dec 20, 2007.

  1. domandrzejczuk

    Thread Starter New Member

    Nov 19, 2007
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    Just doing a homework problem and i need someone to refresh my memory as to under what conditions is a npn transistor turned off, and under what conditions is it in saturation mode?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. domandrzejczuk

    Thread Starter New Member

    Nov 19, 2007
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    Thanks a whole lot!!
     
  4. domandrzejczuk

    Thread Starter New Member

    Nov 19, 2007
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    I'm still not sure if i have this correct. I have a npn transistor where the base is connected to some voltage source vin to a 100k resistorand across a diode. The emitter is connected to ground with no resistor, and the collector is connected to some power source Vcc and goes across a 27k resistor. How would i figure out the voltages for vin and Vcc so that the transistor is in saturation mode?
     
  5. rathinavell

    New Member

    Dec 21, 2007
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    yes.the transistor is go to saturation mode
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    Transistors are really current devices. Place some voltage on the collector resistor for Vcc. Vary the voltage on the end of the 100K resistor. Measure the voltage at the collector. When the current through the base resistor is large enough, the collector voltage will be essentially 0. That means the transistor is in saturation. If the base current decreases, then the voltage between the collector and the 27K resistor will start to increase from 0.
     
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