About a PWM power inverter

Discussion in 'The Projects Forum' started by gaetan8888, Mar 9, 2009.

  1. gaetan8888

    Thread Starter Active Member

    Nov 14, 2008
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    Hello

    I was, since few months, looking for an easy to build PWM inverter, and without any PIC programing.

    Looking at a 555 PWM amp circuit, I have an ideas, by merging a 500 w sine inverter with the PWM section of the 555 PWM amp circuit it made a PWM inverter.

    Here is the final circuit.

    http://img205.imageshack.us/img205/4066/invertersine500wccpwm.jpg

    It should work... I think... ??

    Any suggestions ?


    Thank

    Bye

    Gaetan
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Hello gaetan888,

    Schematic part Fig 72-2 appears to require anti-phased sinusoidal inputs at the LM234 comparators [U4b and U4c]. You have a sinusoidal generator in the XR-2206 already. Why then do you need to interpose a PWM conversion? For me - I doubt the circuit will work.
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Hi again,

    Then again - it may work! - depending on several things.

    What is the PWM frequency? Will you get clean switching at the LM324 comparators. You may need to add some hysteresis there to maintain PWM integrity. Also will U4a inverter switch the PWM signal faithfully.

    Will the transformer handle higher order frequency components OK? Not sure ...

    An so on ...

    I think other electronics experts will have a better idea on the functionality side.

    Good luck!
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The LM324 opamps are way too slow for the PWM signal.
    There is no "dead time" so when one Mosfet is turning on then the other one is still turning off and they short circuit the supply.
    The peak voltage of a 120V sine-wave is 170V, not 120V so the transformer's low voltage winding should be 8.5V, not 12V.
    The mains transformer might not pass the high frequency PWM frequency.
    The output should have an LC smoothing filter to remove the PWM carrier frequency.
     
  5. gaetan8888

    Thread Starter Active Member

    Nov 14, 2008
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    0
    Last edited: Mar 10, 2009
  6. gaetan8888

    Thread Starter Active Member

    Nov 14, 2008
    41
    0
    Hello

    I was looking at a PWM inverter circuit because modified sine inverter are too noisy in TV and audio systems and others things.

    I have a 500 w sine inverter schematic, I have the mosfet and few very big ferroresonant transfo, but it would need a very big heat sink and it would lost quite much energies into heat.

    Here is the original 500w sine wave circuit.

    http://img371.imageshack.us/img371/8734/invertersine500wcc.jpg

    Thank

    Bye

    Gaetan
     
    Last edited: Mar 10, 2009
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I'm afraid it is not so simple. You have to feed your sine wave reference to your 555 PWM. (Note how the Class D amp you referenced takes an input signal.) You must then provide out-of phase signals based on the PWM signal to your MOSFETs. (Note how the square wave inverter from your textbook has out-of-phase sine-waves which drive the MOSFETs.) You must also, as Audioguru has noted, provide "dead time" to prevent shoot-through on the MOSFETs. (Note how the sine-waves driving the MOSFETs in your textbook provide this automatically.)
     
  8. gaetan8888

    Thread Starter Active Member

    Nov 14, 2008
    41
    0
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