Help with PWM a mosfet in multisim

Discussion in 'The Projects Forum' started by Avshi, Aug 26, 2015.

  1. Avshi

    Thread Starter New Member

    Jan 16, 2015
    Hello, this is my first attempt at using multisim and I don't have a huge knowledge base when it comes to electronic devices. I am trying to use this mosfet with the associated spice model files given here (I made my own component, see attached) to modulate output voltage from the mosfet with pmw (to connect directly to a nichrome heating element). The pmw signal was generated with the function generator. I am getting output voltage of 9.895 at 99% duty cycle with 2.5V amplitude offset by 2.5V (to mimic attiny167 pmw output). All this from a 12v source. I tried to increase the dc source to 18V and 50V, but it seems to always stay at 10V no matter what I do. Why is this and how can I fix it?
    Thanks in advance,

    -P.S. Attached is the project file, the component I made as well as a picture of the situation if you don't have access multisim and I wasn't clear enough.
    -P.P.S. I'll be on a plane for the next 20 or so hours and will look at the responses when I get back.
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    Simply connect the Source to GND, Gate to function generator and Drain through a resistor to the positive battery terminal.
    Also do not forget to connect to GND the middle pin of a function generator.
  3. Avshi

    Thread Starter New Member

    Jan 16, 2015
    Wow! thanks! Why does the position of the resistor matter in this case?
    Edit: got a little ahead of myself there. I can control the voltage, but my range is limited to between V1 and V1-2*amplitude. Is this supposed to happen? I wanted a high side switch for the heater, but I'm not sure that really matters.
    Last edited: Aug 27, 2015