Question about a simple transistor switch??

Discussion in 'General Electronics Chat' started by samy555, Dec 31, 2013.

  1. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    Hi

    The first image shows the situation when the transistor works as a switch
    [​IMG]

    In the second photo I connect D2, the result: LED is no longer shine
    My question is why?
    [​IMG]

    Thanks alot
     
  2. tindel

    Active Member

    Sep 16, 2012
    568
    193
    D2 probably has a lower forward bias voltage than the Q2 base-emitter voltage... Which is drawing all the current away from Q2 and doesn't allow the LED to illuminate
     
Loading...