Drive an fet with a 555

Discussion in 'General Electronics Chat' started by arthur92710, Sep 21, 2007.

  1. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
    307
    1
    I finally got some fet's
    SUB85N02 but i cant get it to switch an led on and off with a 555. :mad:
    I need some help
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    555's have no problem driving FET's. Can you post up a schematic so we can see what might be wrong? Sure the 555 is running?
     
  3. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
    307
    1
    the 555 is running on 5sec off 5sec. Ill post a pic in a few.
     
  4. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
    307
    1
    its a n channel 20v mosfet in a To-263 package.
    the pin out is G D S
    g and s are long and d is short nut the metal back is also d
    I have +9 on d (the case), 555 out on g the first one and a led then ground.

    The led does not blink it just stays on.
     
    • fet1.JPG
      fet1.JPG
      File size:
      32.3 KB
      Views:
      130
  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    Arthur,

    The schematic, as drawn, works fine ... with the addition of a resistor in series with the LED.

    There is a discrepancy between what you are saying and what your schematic shows. Clear up those discrepancies and add the values to your diagram.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    With the way you have it drawn, your FET is a source follower, and will have several volts drop across it when it's on. If you reconfigure it as common source, it will be more efficient. See the circuit below.
    EDIT: It came out really tiny. Not sure why.
     
  7. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
    307
    1
    YAY!! IT WORKS!!! Ron you were right!! I did you circuit and it works:) ty
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Oh, gnarly!:D
     
Loading...