DC motor control help

Discussion in 'The Projects Forum' started by wewe, Apr 16, 2010.

  1. wewe

    Thread Starter Member

    Apr 9, 2010
    31
    1
    hello , i made a generator for PWM signals on pic 16f877 , i am willing to use this to control a 1500 W DC motor
    anyway i should have used a pic 18f because it can generate a dead time but it's too late for that , i don't want to re-write any code
    so i would like to know if there's any IC that takes a pwm as an input and the output would be 2 PWMs with a dead time between them
    if now what should i do with the circuit , i need a dead time that is almost 1 micro seconds or maybe 0.5 us
     
  2. russpatterson

    Member

    Feb 1, 2010
    351
    16
    Hi there. I did a motor controller with a PIC12f683 (no dead time PWM) but am only controlling a 15 watt motor. I ran across that deadtime and half bridge PWM stuff in a PIC18 datasheet and I don't really understand how that helps the motor control. Can you explain how it works and why it's necessary? Sorry I can't help you out.
     
  3. wewe

    Thread Starter Member

    Apr 9, 2010
    31
    1
    to control a motor you must have 2 complementary pwms to control a H bridge of transistors (let's say MOSFETS)
    when one pwm is on its rising edge the other is on its falling edge and vice versa , at this time there's a risk of activating all mosfets at the same time , which will cause a short circuit , so you need to generate a pwm where on each rising and falling edge there's a short amount of time where the output of both PWMs must be 0 in order not to risk it , this is called "dead time"
    now , really no one here ever tried to control a DC motor with a pic 18f ??
    its dedicated for DC motors for god's sake LOL
     
  4. russpatterson

    Member

    Feb 1, 2010
    351
    16
    So the H-bridge is to support reversing the motor? I'm controlling a water pump so I don't need reverse.
     
  5. wewe

    Thread Starter Member

    Apr 9, 2010
    31
    1
    yes it should reverse the motor
    and it's a project not a personal choice :p
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    1500 W is a big motor, something like 42 A @ 36 V, & maybe 300A locked rotor; keep tight current control.
     
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