P Channel Mosfet (switching leds).

Discussion in 'General Electronics Chat' started by PVBLLLC, Feb 6, 2016.

  1. PVBLLLC

    Thread Starter New Member

    Feb 6, 2016
    3
    0
    Can some one tell me what's wrong with the attached sketch?
    The p-channel fet/12vLED's won't turn off with the potentiometer.
    I'm using a p-channel fet because the LED array I'm using has 5 segments with a common ground.
    The arduino (bar graph sketch) and potentiometer work correctly with 9 volt LED's.
    Please ref attached.
    Thanks
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    You just hyjacked an older existing thread:
    P Channel Mosfet
    Now you have a thread of your own.

    Bertus
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Where do you think the gate of the fet will get its drive?

    Please post a propper schematic with the schematic symbols in stead of a drawing of the setup.

    Bertus
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
    3,249
    626
    Welcome to AAC!
    You have the MOSFET connected wrong and probably don't need a transistor to drive the gate.
    I don't see a pot in your drawing.

    A "proper" schematic would make it easier to read your circuit. When you post pictures or schematics, please make sure they can be read. I had to use a photo editor to magnify your picture to read the text.
     
  5. PVBLLLC

    Thread Starter New Member

    Feb 6, 2016
    3
    0
    Thanks for the help guys!!!!
    I'm not an electrical engineer, designer, etc.
    Have combined other works to get where I am with this project.
    I don't know how to generate a proper sketch and this is my first post.
    Can you edit my set up sketch showing the proper connections for the MOSFET?
     
  6. PVBLLLC

    Thread Starter New Member

    Feb 6, 2016
    3
    0
    please ref attached bargraph-arduino-demo
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
    3,249
    626
    That doesn't mean you shouldn't learn how to draw a "proper" schematic so that you can communicate in the language that EE's understand.
    This is how I interpreted your "schematic"; I added the ground connection between the battery and the rest of the circuit.
    upload_2016-2-8_6-47-1.png
    This would never work. You have the MOSFET connected backwards and the LED would always be on. If the MOSFET were connected correctly, it would not turn off properly because there's no pull-up on the gate.

    This is how it should be drawn:
    upload_2016-2-8_6-48-47.png
     
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