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LED light

  1. Sep 14, 2008 #1
    Can anyone explain to me why LED2 light only half time compared to LED1? If Us=2sinωt volts
     

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  3. Sep 14, 2008 #2

    Redbelly98

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    Think about what the transistor does when Vs is "high".
     
  4. Sep 15, 2008 #3
    it doesn't help me a lot...
     
  5. Sep 15, 2008 #4

    Redbelly98

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    That's okay, we'll review how the transistor functions in this circuit.

    The transistor has 3 nodes:
    The Base (left side of transistor)
    The Emitter (lower-right of transistor)
    The Collector (upper-right of transistor)

    In this circuit, the transistor acts like a simple switch. When the Base voltage is high, you can treat it as a short between the Emitter and Collector. Which LED or LED's have any appreciable current going through them, if you short the Emitter to the Collector?

    When the Base voltage is low or negative, you can treat the Emitter to Collector as an open circuit, with no appreciable current. If that's the case, which LED or LED's have an appreciable current going throw them?
     
  6. Sep 15, 2008 #5
    I understand it now. Thx for the help!
     
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