Inverter ( NOT Gate ) not working

Discussion in 'General Electronics Chat' started by venkee, Dec 26, 2011.

  1. venkee

    Thread Starter New Member

    Nov 12, 2010
    4
    0
    Hi,

    Newbie question.....


    I am testing a simple inverter I made as per

    http://www.kpsec.freeuk.com/trancirc.htm


    [​IMG]



    At the output I have connected a LED via a resistor.

    Problem: The output ( LED ) is always ON whether the base current is switched on or switched off.

    I attached a LED after the emitter. And this is OK , ie it comes on only when the base current is on.

    Could somebody kindly clarify ?
    Thanks in advance.

    Venkee
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The circuit you're trying to use:
    [​IMG]

    The circuit you should be using instead:
    [​IMG]

    See how similar they are?
    Basically the same thing. Just put your LED in series with Rc.
     
  3. venkee

    Thread Starter New Member

    Nov 12, 2010
    4
    0
    Thank you SgtWookie.

    As I had mentioned, I am testing this circuit and had put the LED only for testing. Actually I need the inverted signal to control another part of the circuit.

    How do I do it then ? ie get the inverted waveform....


    Searching the net for such NOT-gate-type inverter turns up so many circuits but they are so similar to this....

    I dont know what is it that I am doing wrong.


    I have been testing the circuit with 4.5 volts.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    In this case your first circuit should actually work.

    - what transistor are you using?
    - how does the circuit you want to control look like?
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    What is the control signal?

    Double check your wiring.
     
  6. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    your circuit may be picking up noise if the base is floating and the transistor is sensitve enough.....both these circuits work(with an additional pull down/pull up resistor)
     
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