transistor help

Discussion in 'General Electronics Chat' started by Robin Mitchell, Feb 28, 2010.

  1. Robin Mitchell

    Thread Starter Well-Known Member

    Oct 25, 2009
    734
    200
    hi everyone, long time no see

    I have a problem...

    if you have a tran and use it as a switch, does a current still go through if there is nothing on the collector but there is a high current on the base?

    Because that is what i am getting with this 639 transistor :(

    thanks
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Schematic please.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Can you post a schematic of what you are talking about?

    Greetings,
    Bertus
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That sounds a lot like a shorted transistor.

    What is the magnitude of the base current?
     
  5. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    If it is an NPN transistor, then with no collector resistor, the base emitter junction, acts as a forward biased diode, and all current through the emitter flows out the base, which would upset input signal sources.

    Also if input is large enough then the collector base diode becomes forward biased, and a positive signal out the collector would result, but it would be limited by the current flow through this diode junction.

    This is not normal current flow through the transistor.

    Is this the current flow your talking about.

    If not then like "beenthere" said in the above post, it could be a shorted transistor .
     
    Last edited: Feb 28, 2010
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