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Thread: PWM vs CCPWM

  1. Question PWM vs CCPWM

    what is the essential difference between the two? From what i can find online, ccpwm sounds like the lazy man's pwm who don't want to install an ammeter into their system and watch the amp gauge. People trying to sell ccpwm just made it sound like an over-glorified current limiter in my opinion. Someone factually correct me if i am wrong. I was thinking i'd build my own pwm controller with a couple of mosfets and an arduino for under $30 bucks and when you already have all the parts lying around....its free. Also, what is the benefit of frequency control? I get the concept and operation of it, i just don't know why we implement it into the system. Would pulse control by itself be sufficient?

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    I've already done this successfully: /entry.php?4-Arduino-Controlled-PWM&bt=7. This was being hosted over at hodinfo.com, but I think I'm going to have to copy it over where I wish to share it.

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    looks like a really complex system you built. I've got a thread going in the arduino forum http://forum.arduino.cc/index.php?topic=204623.15 but its hard to get straight answers out of everyone who has posted. I'm not even sure what mosfets to use and finding a code to control the pwm frequency is even more difficult which is why I wanted to know if a frequency controller is even that important compared to just pulse control

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    Here is where I will explain the how: http://www.hhoforums.com/entry.php?5...no-Powered-PWM
    Last edited by Stevo; 12-16-2013 at 09:08 PM.

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    will that library let me control pwm frequency using a POT? would a couple of those sparkfun mosfets work better than a couple of these mosfets http://uk.farnell.com/nxp/buk652r3-4...t78/dp/1863285 and a gate driver? I want to use multiple in parallel to reduce heat and enable me to use a smaller heat sink

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    I use 3 of the FQP30N06L MOSFETS in parallel at the moment with the unit I have installed and have tested up to 20 amps @ 14.5VDC with little to no heat using a small 45mm cubed heat sink and same sized slim 12V fan.

    The issue (if any) with the BUK652R3-40C you listed are the "On Characteristics" such as "Gate Threshold Voltage" which is rather low in the FQP30N06L and one of the main selling points. This comment thread helped me to understand this better: https://www.sparkfun.com/products/10...7b7fd351004ebb. Other than that, if you do end up choosing to use a gate driver I would be interested in hearing what your thoughts are after implementing. This might help me make a decision on the bigger unit I have sitting around.

    When it comes to controlling the frequency with the POT, in void setup you have to set the frequency like so:

    //sets the frequency for the specified pin
    bool success = SetPinFrequencySafe(PWMPin, frequency);

    //if the pin frequency was set successfully, pin 13 turn on
    if(success) {
    pinMode(13, OUTPUT);
    digitalWrite(13, HIGH);
    }

    which I have not timed yet or tested during the main loop(). I am unsure as to how much delay calling this method might introduce or if doing so is even possible. This could be a good bench test though..

    Edit: PWMPin is 3 and it's the ATMega 328 Nano.

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    I think I will go with the mosfet you suggested. It's cheaper, easier to get and doesn't require a gate driver (though i was kinda lookin forward to soldering that to a pcb). Now what do they mean in that comments thread about bringing the gate voltage above the rail voltage to get it to fully turn on? I'm not sure what rail voltage means. I have an arduino uno rev 3 and according to their website, pins 5 and 6 have a 980hz frequency and the rest of the pwm pins are 490hz. I'm not real knowledgeable at the technical details of this stuff. Used to be better with the code side of things but haven't touched my arduino in months so i forgot most of it. Can you tell me what the benefit of frequency control is? think i'm just gonna leave that part out, which frequency should i use, the 490hz pin or the 980hz pin?

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    Quote Originally Posted by wikitjuggla View Post
    Now what do they mean in that comments thread about bringing the gate voltage above the rail voltage to get it to fully turn on? I'm not sure what rail voltage means. I have an arduino uno rev 3 and according to their website, pins 5 and 6 have a 980hz frequency and the rest of the pwm pins are 490hz. I'm not real knowledgeable at the technical details of this stuff. Used to be better with the code side of things but haven't
    According to what I've read, rail voltage is basically the voltage read at the filtering or stiffening cap(s) connected to the source pin and +. In this case it would be ~14VDC.

    This document is super informative: http://www.fairchildsemi.com/Assets/...OSFETs-PPT.pdf
    Last edited by Stevo; 12-18-2013 at 04:44 AM.

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    I had a feeling thats what rail voltage was. Do you use a gate driver on your module or just an arduino pin? what is the current draw per mosfet on the gate pin? That document helped a little bit but all those symbols are just really confusing. Looking at a mosfet datasheet gives me a pretty good idea of what it must feel like to be dyslexic. For such a tiny little thing, they are ridiculously complex

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    Quote Originally Posted by wikitjuggla View Post
    Do you use a gate driver on your module or just an arduino pin? what is the current draw per mosfet on the gate pin?
    No, I don't use a gate driver. Not yet..

    http://www.hhoforums.com/entry.php?5...-PWM#comment16
    Last edited by Stevo; 12-18-2013 at 07:11 PM.

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