Circuit Theory of Operation

Discussion in 'General Electronics Chat' started by kurt.brinker, Nov 9, 2009.

  1. kurt.brinker

    Thread Starter New Member

    Nov 9, 2009
    New guy here and i could use some help on this. I can't get a clear answer from anyone i work with so here we go.

    We are using a digital output as the input to a vfd. The only way i know to do this is with pwm so i assume that is how its being done. This is the exact circuit. Part of what confuses me is the fact that the opto-coupler is listed as having a 5V input.... We can use a 5V output so why use 24V?

    If someone could throw out some theory of operation, that would be great.

    I have rarely ever had to go down to component level on things so bear with me.

    24V-------680Ω----------A1 on opto coupler
    Digital Out----------------A2 on opto coupler
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    What is the part number on the opto-coupler?

    Some VFDs use an analog input, where the speed is proportional to the analog voltage (or current). When you say PWM, is the signal being passed through the optocoupler a 5V PWM logic signal? If so, the 5V on the input side says nothing about what the VFD wants on the opto's output. It could require a 24V signal.
  3. kurt.brinker

    Thread Starter New Member

    Nov 9, 2009
    the opto coupler is a Pheonix DEKO-OE-5DC/24DC/100KHZ

    The vfd input is indeed analog and yes it is my belief that the signal being passed through is a pwm logic signal. I am confused as to why we use 24V on the input side of the optocoupler. I also assume the reason for the resistor is to limit the current of the circuit??

    attached is a diagram of the vfd input which is either 0-5 or 0-10
    10--- +
  4. Dave

    Retired Moderator

    Nov 17, 2003
    The last post of this thread got lost on the moderation queue.

    I have jumped this thread up the forum listings. Apologies for the inconvenience.