Change Transistors Working Point!

Discussion in 'The Projects Forum' started by anomalyz, Apr 29, 2010.

  1. anomalyz

    Thread Starter New Member

    Mar 21, 2010
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    How can I lower the working point of a Tip31. I need to be able to use it at a slightly lower voltage.
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    A little more info, please.

    What is your intended voltage?

    do you have a schematic?

    Can you explain what you hope to achieve with this circuit and why you feel you need a lesser voltage?

    Why not use a NPN with the ratings you require?
     
  3. anomalyz

    Thread Starter New Member

    Mar 21, 2010
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    I built the circuit from this website-http://www.instructables.com/id/Music-LED-Light-Box/step6/Building-the-circuit/
    When I use my ipod I have to turn the volume almost all the way up before the lights start to go to the music. I added speakers to the circuit and do not want them at full volume to go with the lights. I need the transistor to allow the lower volume on my ipod to start and light up the lights. Hope this helps!
     
  4. retched

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    Dec 5, 2009
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  5. anomalyz

    Thread Starter New Member

    Mar 21, 2010
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    I used a 9V battery instead of the 12V to power 4 2.2V leds. I added two speakers to the audio of the left right wire from the audio jack - not going through the transistor. Tip31c
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    Yes, you need more a different NPN. the tip31 requires more voltage than you are providing.

    Check the link on post #4. Read that for good ideas and other parts.

    Each of you 2.2v leds are reducing the voltage.

    4 leds at 2.2v each is 8.8v.

    8.8v - 9vbattery leaves only .2v to power the transistor.
     
  7. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Hi

    It is a good idea to measure some output voltages from your IPOD, so as to have an idea of what voltages to design for.

    If you have a voltmeter, put music in your ipod, and using the jack hook up your voltmeter with a DC setting,

    than turn the volume to minimum, and record peek voltages, just find a round off number, as there changing so fast with the music.

    then set the volume for high, and write down the peek voltages, again.

    Then set the volume in the middle, and write down the peek voltages.

    That way your letting people know what voltages to design for.
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    Instructables are written by people who know nothing about electronics.
    The circuit you linked to has no biasing for the transistor, no base current limiting, no reverse emitter-base voltage protection and no current limiting for the LEDs.

    The MP3 player might blow up its output trying to drive the base-emitter junction of the transistor with nothing to limit the current.
     
  9. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Hi,

    You can try this,
    It works at a min. of 200mV pk.

    ipod leds.jpg

    I used 4 green LED's, and designed it for 8v. so 9v. battery will work fine for it.

    The input resistance is low though, less then 700 ohms, it may work depending on what your IPOD can handle with impedances.

    Also uses some current too, but its a start to get you in some direction for your project, you can add to it or deviate from it to make it suit your wants..
     
    Last edited: Apr 30, 2010
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