PWM w/ Variable Width

Discussion in 'The Projects Forum' started by xxbleh, Mar 1, 2012.

  1. xxbleh

    Thread Starter New Member

    Mar 1, 2012
    3
    0
    Hey,

    I'm having trouble with my circuit. I have a comparator that will compare a sawtooth oscillator (voltage reference) and a variable AC voltage (1-10V). I need the circuit to work as:

    1V --> 10us
    10 --> 1us


    COMPARATOR: CD4007's
    SAWTOOTH: PNP's, NPN's, and diodes
    AC VOLTAGE: POTENTIOMETER

    So far, I got the circuit to work partially. However, the only problem is that I can't get the requirements for the width at the certain voltage. I play around with the caps and resistors of the sawtooth, but I can't get it to work :(

    FIRST PICTURE: Overall Ckt
    SECOND PICTURE: VIN --> 1V
    THIRD PICTURE: VIN --> 10V
     
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  2. xxbleh

    Thread Starter New Member

    Mar 1, 2012
    3
    0
    bump. BUMP. bump.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,019
    3,235
    Hey yourself,

    You are getting a little less than 2μs at 10V input. In order to get 10μs at 10V you will need to reduce the frequency of the sawtooth by over a factor of 5. For that I think you will have to increase the value of R5 and C1 so that the time constant R5C1 is a little over five times larger.
     
    xxbleh likes this.
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