Transistor Switching, Minimum current for base?

Discussion in 'General Electronics Chat' started by Ishiyuu, May 25, 2016.

  1. Ishiyuu

    Thread Starter New Member

    May 25, 2016
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    Hello all,

    I have a very general question that seems to not yet have been answered. In a circuit I am designing, What I want is a 2n2222 transistor to only fire above a certain current. In a simulator, I am applying a 361.1uA current to the base, and am getting a 36.1 mA current. In reality, is it possible to completely limit the emitter current to 0 without the base being 0?
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Welcome to AAC!

    How close to 0 do you require? Even with a large base resistor, there will be some leakage current.

    For anyone to be able to comment on the circuit you're simulating, you need to post a schematic.
     
  3. Ishiyuu

    Thread Starter New Member

    May 25, 2016
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    My apologies. My primary objective is to create a circuit whereby after 1 second of conducting, the circuit becomes "opened" for a period of time, where the base and collector connected cannot conduct current. I want to create this circuit in the most simple way as possible, without the use of gates or IC's.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    If you want the transistor to be saturated for a certain period after being triggered, you can make a discrete one shot to drive the switch. That will take 3 transistors, a capacitor, and some resistors.

    From wikipedia: https://en.wikipedia.org/wiki/Multivibrator
    upload_2016-5-25_7-54-31.png

    You could try using an RC network on the base of a transistor, but you won't get a sharp on-off transition.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    How long is this "period of time"?
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yes. First, there is a minimum base-emitter voltage below which no base current flows. Once Vbe is large enough and base current does start to flow, there is a minimum current necessary to start collector-emitter conduction. These values are on the datasheet.

    ak
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    No. If there is any base current whatsoever, it appears at the emitter. It cannot accumulate in the transistor!

    Now, you could have a base-collector current if the collector voltage falls below the base voltage. But I don't think that's what you are asking.
     
  8. Ishiyuu

    Thread Starter New Member

    May 25, 2016
    3
    0
    Thanks for the suggestions. I have found another solution however; I will use a relay instead
     
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