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  1. #1
    alpha-dog Guest

    Single chip solution pwm

    This is a TL494 pwm I've built for the P-Channel mosfets. It will work with the N-channel mosfets also but you need to reverse pins 15 and 16 inputs.

    Attachment 1214

    This pwm does everything that the ZFF does and more. Although I only show here current limiting, duty cycle adjust, and PRF ( frequency ) adjust, there's also Dead time and a control that allows for two outputs with 48% max duty cycle at 180 degrees out of phase.

  2. #2
    drumacc Guest

    bigger

    This post is 6 months old, I know, but do you have a larger version of your sketch? Can't make this one out...

  3. #3
    alpha-dog Guest
    This should be larger


    Attachment 1217

  4. #4
    Join Date
    Nov 2008
    Posts
    5

    ?

    Sorry still cant see the values of the resistors and such. Looks great from what i can make out tho. Any chance you can make one slightly bigger again?

  5. #5
    alpha-dog Guest
    It's really big on my machine. I've had this problem before on this site.
    If you want to build one of these, I get my components from digi-key.

    part
    digi-key part number
    amount

    tl494
    296-1799-5-nd
    1 $.52
    100k trimmer pot
    490-2876-nd
    1 $ .86
    10k trimmer pot
    490-2875-nd
    2 $1.64
    5.1k resistors
    p5.10kcact-nd
    5 $.32
    1k resistors
    1.00kxbx-nd
    5 $.32
    220 ohm resistor
    p220cact-nd
    5 $.32
    .1uf cap
    2
    .01uf cap
    1

    tl494 pin-out
    pin 1 connect center conductor 10k trimmer and then one side of pot to grnd and the other side to Vref ( pin 14 )
    pin 2 connect to 5.1k resistor to pin 3 and connect another 5.1k resistor from pin 2 to grnd
    pin 3 connect 5.1k resistor from pin 3 to pin 2
    pin 4 connect to grnd
    pin 5 connect to .1uf cap ( Ct cap used in Osc. ) and connect other side of cap to grnd
    pin 6 connect a 1k resistor: connect 1k resistor to 100k trimmer pot connect center conductor of pot to one end conductor then end conductor to grnd
    pin 7 connect to grnd
    pin 8 Vc output connect to pin 11
    pin 9 Ve output connect to grnd
    pin 10 Ve output connect to grnd
    pin 11 connect to 220 ohm resistor and other end of resistor to pin 12: connect to .1uf cap and other end of cap to grnd: connect to 1k resistor
    and other of resistor to grnd
    pin 12 connect to +12vdc filtered power ( pwr run circuit used by ECU is already filtered, this would be switched power )
    pin 13 connect to grnd
    pin 14 Vref output to high side of both 10 k trimmer pots
    pin 15 to center conductor of 10 k trimmer pot: one side of pot to grnd and the other to Vref
    pin 16 to Rshunt ( 8" of 12 guage solid conductor wire in grnd path of electrolyzer )

    I us the breadboard from radio shack ( 2 boards in one package )
    I also use there project box and terminal board

    When setting up your pwm adjust pin 15 to about .5vdc and pin 1 to about 2.3vdc. You can adjust pin 6 to ground for 101k ohms for the lowest freq.
    Make sure that pin 15 is a higher voltage than pin 16.
    pin 1 sets your duty cycle and looking at pin 3 you can see a dc output from pins 1 and 2. Pins 15 and 16 make up the current limiting comparator. You will adjust pin 15 once the system is hot.

    If you would like to try one of these but don't want to build it yourself, PM me about building you one. I can also make it work for N-channel mosfets, but it is for P-channel mosfets.
    Russ

  6. #6
    Join Date
    Jan 2012
    Posts
    3
    Hi,

    I'm new here, and would like to ask whether anyone was able to build this pwm with N-channel mosfets and ask his/her opinion/feedback about that pwm. I have built it with N-channel, and reversed the 15 and 16 pins, I could set .5vdc on pin 16 and 2.3vdc on pin 1 and could also set the frequency, but still I cannot regulate the current as i wish. Neither the freq. nor the duty cycle nor the current can be set or regulated. The HHO generator always works on maximum current,(as it is getting hot, it takes up more and more current) and the current can't be regulated.
    If anyone can help me, please answer soon.

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