P-Channel MOSFET

Discussion in 'General Electronics Chat' started by Tobias, May 1, 2009.

  1. Tobias

    Thread Starter Active Member

    May 19, 2008
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    I am making a device for a friend that needs to switch 16v power on and off. He wants to switch the power and not the ground. So I bought a MOSFET from Mouser, http://mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMveMCOqFR6qCL5od2AuAbDnWGlf1ag0e1Y=

    This is my first shot with MOSFETS. Last night I was playing around with it. I have the Drain tied to ground through a 22k resistor to give it some load. On the Source side I have 12v. I noticed that when I ground the Gate, it turns 'on' the MOSFET and I have voltage on the Drain side. I tried to use 5v to switch 'off' the MOSFET and that didn't do the trick. I had to give the Gate 12v to turn 'off' the MOSFET.

    Is this normal? Or do I need to find a 'Logic-Level P Channel MOSFET?' Can anyone recommend a part number is thats the case?
    Thanks
    Toby
     
  2. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Can you post a wiring diagram of what you want to do. Do you have to switch it on/off with 5 volts. What is the load. Sounds like you might need a logic level mosfet,or you could use a small signal transistor (npn) turned on by the 5v to ground the gate. If we have a diagram to go by, we can supply more info.
     
  3. Tobias

    Thread Starter Active Member

    May 19, 2008
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    Attached is a schematic. I want to switch 16v on Clutch-Out, L/L-Out, Aux Out 1, and Aux Out 2 with a PIC chip based on conditions of four inputs.

    I am learning about the MOSFETS. I need a P-Channel I think to switch the 16v. It needs to handle min 20 Amps.
     
  4. Wtech

    New Member

    Apr 27, 2009
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    I used the configuration as shown in attach picture. Base of BJT or gate of small power N type MOSFET is driven by microcontroller directly. Normally microcontroller pin is low and BJT will remain OFF so at collector there will 12V, for PFET gate and source are at same level so FET will also remain OFF. Conversely when microcontroller high the pin, BJT will ON, at collector there will 0V, and FET will also ON because of Vgs = -12V
     
  5. gerty

    AAC Fanatic!

    Aug 30, 2007
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    This is how I switch some emergency lights, they aren't nearly as high in current, but it'll give you some idea of what I'm talking about.
    Anymore questions, just ask.
     
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Another thing you might want to look at is your indicator led. You have it tied to the gate of the transistor. You should have a resistor for each led, separate from the transistor.
     
  7. Tobias

    Thread Starter Active Member

    May 19, 2008
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    thanks guys
     
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