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Parallel versus Series Resonance Converter Topology - Pros/cons

Discussion in 'Electronic Design' started by Klaus Kragelund, Jan 4, 2006.

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  1. Hi

    I'm working on a resonance converter and have read a little bit on the
    subject thus far. Most recommend using a series resonance topology, but
    I cannot seem to find the excact reason why the parallel resonance
    converter is disregarded.

    The block diagram is a follows:\tmp\parallel_resonance_conv.jpg

    In this parallel resonance converter the OSC is adjusted to exactly the
    resonance frequency. Offcourse this will let the voltage envelope
    continue to rise on the LC circuit, but that is taken care of by the
    optocoupler which will shut down the driver when the voltage is to high
    on the output

    So in essence the converter is operating burst like on the resonance

    In this converter the current is cycled between the L and C in the LC
    circuit, so there is little current in the driver. On the contrary the
    series converter has large current in the drive.

    But what is the drawbacks to an parallel LC circuit like this versus a
    standard series LC resonance converter? Something that I'm missing?


  2. Tim Williams

    Tim Williams Guest

    Transistors are most efficient switching quick and solid. A capacitor is
    like a train hitting a brick wall. Series resonant has an inductor in
    series, so the switching harmonics are handled softly. Peak currents are
    low and the world sleeps soundly.

    If you must have a parallel resonant tank, you can feed it with a series
    inductor (check my website for a related project), but the behavior is a bit
    more complicated (showing both series and parallel resonant behavior).

  3. There isn't any - it depends on what one needs the converter to do. In
    general, parallel resonant converters tend to be current-fed i.e. large
    inductor on the input, so they regulate slower. The Mapham Inverter is the
    classic version. Other kinds work on dumping energy into the parallel tank
    and regulate by changing the dump frequency - Philips did a "Parallel
    Resonant Power Supply?" PRPS application note.

    If your reason for wanting a resonant converter is getting a clean
    sinusoidal output voltage then the large parallel capacitor on the output
    helps a good deal. Often those converters are running at a *fixed* frequency
    and the output voltage is controlled by adjusting the Inductor part of the
    L/C resonator (For large setups, such as an UPS, the "inductor" is a
    full-bridge feeding a constant current DC/DC converter - the current sets
    the "Inductance"). Cancelling part of the flux by transformer action can
    work too.
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