Could you purpose any IC for PWM generator?

Discussion in 'Homework Help' started by theasus, Jan 1, 2010.

  1. theasus

    Thread Starter New Member

    Sep 12, 2009
    Could you purpose any IC for PWM generator?
    Desired frequency interval is 1Hz to 300Hz.
    I found some like 8038,XR2206 but they are very old IC and it is hard to assure these IC.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. Wendy


    Mar 24, 2008
    The 555 is much like a swiss army knife, you can approach this problem several ways. Here is another oldie but goodie.


    I pulled this schematic from chapter 5 of this article...

    LEDs, 555s, Flashers, and Light Chasers
  4. thyristor

    Active Member

    Dec 27, 2009
    This what I designed for my boat as a 12v lamp (and fan) dimmer. It gives full control from 0 to 100% using a single LM324. Frequency of operation can be set as per the formula on the diagram.


    The output of the integrator is a linear ramp that goes from about -3v to +3v (referenced to the mid-rail). When this output value is higher than the voltage set by VR1, the comparator output goes positive and the MOSFET turns ON switching on the lamps. When the integrator output is below the voltage set by VR1, the lamps are OFF. The output of the integrator also feeds the Schmitt trigger thus forming a regenerative loop (oscillator) which produces a square wave at the output of the Schmitt and the linear ramp at the output of the integrator.

    VR1, R6 and R7 are calculated such that the voltage at VR1 wiper can be set just below -3v to just above +3v (referenced to the mid-rail) allowing full 0 to 100% control of the lamp brightness.

    If anyone wants to know how the frequency formula is derived, I am happy to add it to the thread.
    Last edited: Jan 5, 2010