Sinewave power question:

Discussion in 'General Electronics Chat' started by howhurley, Feb 5, 2009.

  1. howhurley

    Thread Starter Member

    Feb 1, 2009
    As some of you know, I have been working on a special inverter taking 100-150 VDC and transforming it into 117 vac. My modified sinewave I spoke of last week just isn't feasible because of the noise.

    One of my highschool daughters asked me (yes, she's a brainiac) yesterday a stupid question that turned out to be smarter than me.

    She asked me if I could just take a low power sine wave generator, feed it into a 600 VDC 15 A full-wave H bridge and use the output directly. Well, I can see that the DC isn't high enough magnitude, but if I doubled the DC, biased the unit so I could use the most linear area of the bridge, wouldn't that work? This would save me a lot of board space and trouble, if that's all there is.

    Don't beat me up, folks.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    The advantage of the H bidge is in that the switching components operate either in the non-conducting or fully conducting state. This minimizes ohmic losses by keeping the IGBT's or FET's out of the linear region.

    Driving with a sine input runs the devices exclusively in the linear region. The same would take place if you were to use a big audio power amp to generate the 60 Hz waveform. In fact, an audio amp would work better, as it has feedback built in to control the output accurately.

    Take a look at the linear region in a power FET. It's very small, and not consistent device to device. Beside the tiny region of linearity, the package is not good for linear operation. You might need a water cooled heat sink.
  3. howhurley

    Thread Starter Member

    Feb 1, 2009
    So is there anything you could think of that would provide enough power (5A with a starting surge of almost 15A) at 117 vac, driving an inductive load?

  4. Audioguru


    Dec 20, 2007
    Inverters with pure sine-wave outputs use high frequency Pulse-width-Modulation to drive the switching devices. Then a small simple filter is used at the output.
  5. bertus


    Apr 5, 2008