SINE inv, need help

Discussion in 'General Electronics Chat' started by raffter, Aug 1, 2008.

  1. raffter

    Thread Starter Active Member

    Feb 28, 2008
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    guys,

    I have seen before the guts of some sine output inverters.. it used an SG3525 chip to drive the MOSFETS.... and a PIC(to control the PWM chip)..but sadly I threw it away in a junk pile..never hada chance to examine it :(

    I want to make something similar..perhaps

    been reading something about "magic sine" on the net..quite aware how the PWMs look like(for an approxiamation of a sine)

    now my question is: since normally(almost all) inverters use push-pull topology with the 3525, (presumably running @ 50Hz or 60Hz), HOW can I "CHOP" the the output/s of a 3525 so that each output will PWM an aproximation of a 1/2 cycle sine(PWM controlled my a PIC)?? presuming that is the right way.....

    will the 3525 reset itself IF I inject the PWM from PIC??


    Ralph
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    The 3525 is designed for hundreds of kHz PWM.
    The inverter makes a 50 Hz or 60 hz sine-wave by switching the 3525 outputs and Mosfets at a high frequency then filtering the switched high frequency PWM output into a sine-wave.
     
  3. bertus

    Administrator

    Apr 5, 2008
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  4. raffter

    Thread Starter Active Member

    Feb 28, 2008
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    dear bertus,

    I know how to use GOOGLE... you type in www.google.com and press the button labeled <-ENTER...then type in the keywords you want to know...seriously, HOW would I have found that "magic sine" w/o searching it on the web... :)

    I specifically wanted MORE info about UPS/inverters using a PIC/and SG3525... I already have made (in PIC) a series of pulses(to aprrox a 1/2 cylce sine) going to an SG3525 in push-pull mode.... and was asking IF this was the correct way....

    No offense.. And I hope Im very clear here..

    thank you

    Ralph
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    How did you connect the pic to the sg3525?
    The sg3525 is basicaly a stand-alone switching power supply, motor speed control or power converter.

    Do you have a schematic?

    Greetings,
    Bertus
     
  6. raffter

    Thread Starter Active Member

    Feb 28, 2008
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    Hello Bertus,

    Im in the process of finding that out(how IS the connection made)..... my idea is a PWM(from PIC) of 1s and 0s sent to the (maybe) shutdown pin of SG3525 run in 50/60Hz push-pull....

    or maybe im not in the right direction...on how to control the outputs....

    "magic sine" from don lancaster.. have a look....

    -Ralph
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Shutting down the sg3525 will stop the pulses on all outputs.
    How many volts are on the drive side of the transformer?
    The PIC is working at 5 Volt, so you need to interface to the drive voltage.
    My idea is pretty simple.
    The magic sine signal is coming from a pin of the pic.
    Send the pos. part to one driver and the neg. part to the other driver.
    In this way you don't need the sg3525.

    Greetings,
    Bertus
     
  8. raffter

    Thread Starter Active Member

    Feb 28, 2008
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    here is the simulated output from my PIC

    [​IMG]

    IF I would ONLY need a PIC,then its mandatory I add fast-switching buffers prior to driving the MOSFETs....

    I wonder if (lets say) I drive the shutdown pin of SG3525(through the PWM from PIC) if it still "retains" the "length" of the pulses going to the MOSFETs... say a PWM of the half-sine cycle of the 3525 push-pull outputs..

    ----------------
    or lets make the "output" of SG3525 to be the same as the image I posted... lets assume IT is the output of the 3525 if it HAS BEEN PWM controlled through the shutdown pin.... IS this possible also?? sort of "gating" the outputs of the 3525 by the PIC...

    I hope my explaination is clear enough


    Ralph
     
  9. bertus

    Administrator

    Apr 5, 2008
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  10. raffter

    Thread Starter Active Member

    Feb 28, 2008
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    regarding mosfets driving, I have it all figured out already..and is of no big concern to me really..

    sigh...seems like my question is NOT being answered ...I guess Im off on my own..

    thanks anyway...

    -Ralph
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like you can use the Sync input (pin 3) to input the PWM signal.
    This seems to be used for synchronizing 2 or more sg's.
    See datasheet.

    Greetings,
    Bertus
     
  12. raffter

    Thread Starter Active Member

    Feb 28, 2008
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    I have made another aproach to this... 1st is a boost converter then "chopped" to generate pseudo sine wave(PWM) w/c is controlled by the PIC...maybe I can "play" with the PWM timings for effeciency(but more on that later)... I made a small prototype and is now working... bUT I limited the output to 22VAC.. I still need to find HV FR diodes..and LOWER RDSon MOSFETs...so I can acheive 220AC output...
     
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