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Transistor problem

Discussion in 'General Electronics Chat' started by Solid Snake, Jan 9, 2003.

  1. Solid Snake

    Solid Snake New Member

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    I want to control a 12v line with a 5v TTL voltage. I used a transistor but the problem is, with a 5v input, I only get a 5v output. It seems that the transistor is not amplifiying the voltage as I thought it would do. I have +12v on the collector, the load between emitter and ground, and 5v on the base through a resistor. I only get 5v on the emitter. Is there any way I can do this with a transistor? I want to stay away from relays.
     
  2. herbymcduff

    herbymcduff New Member

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    if you are wanting a 5v output to supply TTL devices, then it seems to me that your circuit works.
    Maybe you should use a voltage regulator like a 7805. With 12 volts in, you would get 5v out. And it is much more reliable than a transistor.

    It also seems that you are confusing the transistor. You said you have 12v on the collector, and five volts going in on the base. Are you using two supplys? Now if you used a voltage divider on the base, and got 5v thats fine. But you also said you are taking your output from the emitter. And you said that you had five volts out. Impossible. You would only get 4.3 because of the base to emitter voltage drop.

    Also, if you want to amplify the voltage, you would have to take the output of the collector. But your not amplifing DC. You would only be amplifing AC if you had it inputed on the base.

    So a little more info would be great.
     
  3. Sebi

    Sebi New Member

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    Yes,but You need two transistors. One PNP serial ,emitter on+12V, collector is out, and other NPN, collector to PNP base with serial resistor,emitter to GND (-) base with serial 2k resistor to TTL out. Sometimes need 1...2k resistor between PNP emitter-base for correct closing.

    I hope this help for You.

    P,S, Sorry for bad english, i never learn....
     
  4. dave

    Dave New Member

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  5. Solid Snake

    Solid Snake New Member

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    No, I 'm already using a voltage regulator to get TTL voltage. I want to use TTL voltage to control a 12v device. The problem was that I was using a common collector arrangement which has a gain less than one. I changed it to a commen emitter arrangement and it works fine now.
     
  6. Sebi

    Sebi New Member

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    O.K. but when the load is on GND(-), switch serial in positive line and supply voltage higher as control voltage You can always use PNP-switch arrangement.
     

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