Transistor help

Discussion in 'The Projects Forum' started by timplett, Jan 25, 2009.

  1. timplett

    Thread Starter Member

    Jan 20, 2009
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    I want to use a transistor to power a motor but I need the motor to run when there is 0 volts to the base and shut off when the base receives voltage. How do I do this?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Use PNP transistor instead of a NPN one. What is the voltage and current ratings of the motor?
     
  3. timplett

    Thread Starter Member

    Jan 20, 2009
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    I am not exactly sure of the size motor I will be using yet for this project. It will be 12 volts and I think under 10 amps.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If it's more than a few Amperes, you'd be better off using an N-channel power MOSFET; they're much more efficient power-wise than using transistors. A P-channel power MOSFET could be used, but they are typically less efficient than their N-channel counterparts.

    Once you figure out what your input signal will look like, and how much power your motor will require, we can be of more help.
     
  5. timplett

    Thread Starter Member

    Jan 20, 2009
    19
    0
    I am planning on using a monostable 555 circuit as was suggested to me by mik3 so the output of the 555 will be the input to the base of the transistor. As far as the motor as I said I am not completely sure yet but lets say 5-10 amps @ 12VDC. If anything it may be less than 5 amps, but not significantly.
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Use a n channel MOSFET driven by a BJT as to turn it on/off fast and not allow it to spend much time in the linear region and dissipate much heat.
     
  7. timplett

    Thread Starter Member

    Jan 20, 2009
    19
    0
    Would that still be a PNP BJT?
    I was searching for MOSFET transistors for sale and this one would more than handle the load and the datasheet (http://www.datasheetcatalog.org/datasheets/50/118235_DS.pdf) says it can be operated directly from integrated circuits. Would you still recommend the BJT?
     
    Last edited: Jan 28, 2009
  8. timplett

    Thread Starter Member

    Jan 20, 2009
    19
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    I was actually just doing some further research on the 555 and stumbled across a monostable circuit with the output normally on. Does this make it simpler at all?
     
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