Choosing the right Transistor

Discussion in 'General Electronics Chat' started by bhaazee, Jun 15, 2012.

  1. bhaazee

    Thread Starter New Member

    Mar 3, 2012
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    I have been trying to choose the right transistor for lighting a 5v LED. However simply searching on ebay gives different results (MPSA42, AC176, BC550, ON222 and so on). Trying Google to find the right transistor is still in-vain. Looking for suggestions

    Regards
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    There may be literally thousands of transistors types that will work in your application, so you can get really picky as to package size, price, color, and other things you perhaps never considered to be "design electronics."

    That said, I keep a bunch of parts that end with "2222A" (such as 2N2222A) in my parts bin for times I need something in an NPN. I have a few parts with leads, but most are SOT-23 packages as I prefer to breadboard with SMD parts.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    Transistors are categorized by many different parameters.
    The main ones of our concern are:

    type of material (germanium Ge or silicon Si)
    polarity (PNP or NPN)
    maximum or breakdown voltage
    typical operation current
    power dissipation
    maximum frequency of operation
    current gain

    Controlling an LED at 5V falls under the less demanding applications.
    Hence just about any transistor will work. For the most typical circuit configuration an NPN transistor such as 2N3904 or 2N2222 will work.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  5. bhaazee

    Thread Starter New Member

    Mar 3, 2012
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    Thnx for the replies. But, if possible could you explain me what 2222 or 3904 means (would like to learn it :))?
    I believe 2N means NPN
    Also the Transistor spec says 40V (Is this the rated voltage?) None of transistor spec gives the min. voltage needed to toggle. Is there a min. defined voltage value at which a Transistor could operate?
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    The letters and numbers mean very little.
    No, 2N does not mean NPN. 2N3906 is a PNP BJT.

    Treat the letters and numbers like the license plate on a car. It is just a registration number.

    When a transistor is rated at 40V it means do not exceed 40V.
    Typically, transistors can operate down to 1-2V.
    Special low voltage devices can operate below 1V.
     
    Last edited: Jun 15, 2012
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