Connecting a bipolar transistor.

Discussion in 'General Electronics Chat' started by GASANT, Feb 6, 2013.

  1. GASANT

    Thread Starter New Member

    Apr 30, 2012
    4
    0
    Hi Everyone

    I am trying to connect a NPN Bipolar Transistor to a led light.(experimenting)(trying to understand)

    Here is what I am using.


    1) 10v power supply for collector
    2) 5v power supply for base.
    3) green led light
    4) NPN transistor.

    I connect 5v positive to base of transistor.
    I connect 10v positive to positive led light and negative to collector.
    I connect 10v and 5v negative to emitter.

    The result is the led does not light up.
    Please help. What am I doing wrong


    Thank you
    Gasant
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The Completed Projects Forum is for Completed Projects only. It is meant to allow members to show plans for projects they built so other members can duplicate them if desired. New threads are also automatically moderated per Moderator review for this reason. Your thread does not belong in this forum, and was moved here.
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    ...take a look at this...and this...
     
  4. w2aew

    Member

    Jan 3, 2012
    219
    64
    ...without using an resistors for current limiting as shown in the links listed above, you likely would have smoked the transistor by connecting 5V between the base and collector.
     
  5. SPQR

    Member

    Nov 4, 2011
    379
    48
    From one Noob to another:)

    Here are some of the "rules" I've learned.

    1. EVERY LED needs to have an appropriately calculated resistor connected to it to limit the current to the level recommended by the datasheet and or adjusted slightly for a light output that works for you.

    2. Read the datasheet for the transistor, looking at maximal collector-emitter current (this will tell you if the transistor can "drive" what you want to drive).

    3. Learn how to calculate a base resistor/current - this is very instructive particularly about how the transistor works in general.

    4. For a "transistor as a switch" the base current needs to put the transistor into the "saturation" zone.

    As soon as you pick a couple of resistors, you'll see it work nicely.
    Think about using some pots to "play" with your system.


    I went through the same thing a few months ago, and I've learned a lot from this forum since then.
    There's a little transistor project I'll post on the projects forum for comments over the next week.
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    +5V on the base and 0V on the emitter without a current-limiting resistor causes a very high current which blows up the base-emitter.

    Why use an emitter-follower transistor anyway?
     
  7. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    Just to give you an idea connection wise-heres 2 simple circuits using an npn transistor in one and a pnp in the other.....
     
    SPQR likes this.
  8. GASANT

    Thread Starter New Member

    Apr 30, 2012
    4
    0
    HI

    Just need to thank everyone whom tried to help me.

    Bit late. Nevertheless.

    Thank you
    Gasant
     
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