Algorithm for a program to generate pwm signals using pic 16f877

Discussion in 'Embedded Systems and Microcontrollers' started by varunkumhar, Jan 8, 2010.

  1. varunkumhar

    Thread Starter New Member

    Jan 8, 2010
    hi.i am currently working on a project which converts a 50 hz frequency input into 800hz frequency output.the principle employed is to first convert the input ac to dc using a rectifier and then to use an inverter to convert this dc to the ac output at the required frequency. i am planning to implement the inverter using a mosfet bridge which is triggered by pwm signals supplied by means of pic 16f877 microcontroller. please help me with the pic programming. i would be very thankful if anyone could post the program or algorithm
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Why do the up conversion? Use some fixed oscillator to generate a frequency and divide it down to 800 Hz.
  3. varunkumhar

    Thread Starter New Member

    Jan 8, 2010
    hi thanks for your reply.mine is an industrial project.the company requires 800hz for transformer testing purposes.please help me with the pic programming to generate pwm signals to trigger the mosfet.
  4. SgtWookie


    Jul 17, 2007
    Well, if you take a 50Hz AC signal and run it through a full-wave bridge, the output will be DC with 100Hz ripple.

    What are you trying to do; create a pseudo-sinewave output via PWM? Or are you trying to simply perform a push-pull conversion?
  5. Markd77

    Senior Member

    Sep 7, 2009
    You should be able to get 800Hz with a 4MHz clock.
    Just use the formulas in section 8.3 of the datasheet, ie:
    PWM period = [(PR2) + 1] • 4 • TOSC • (TMR2 prescale value)
    With 4 MHz clock TOSC would be 0.00000025
    and 800Hz is 0.00125
    PR2 should be 77 (decimal) and TMR2 prescale should be 16
    This gives 801.28 Hz
    You will need to do a similar calculation for the duty cycle.
  6. Art

    AAC Fanatic!

    Sep 10, 2007
    The 16F877 has a hardware PWM pin.
    You can just set it and your program can run at the same time.