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Half-Bridge or Full-Bridge SMPS?

Discussion in 'General Electronics Discussion' started by eem2am, Sep 3, 2011.

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  1. eem2am


    Aug 3, 2009
    I think that Offline Half-Bridge converters are a complete waste of i right?

    The full-bridge is cheaper and better......

    FET RMS current will be much higher with a half-bridge than a full bridge, and the half-bridge fets will need to be more pricey with bigger heatsinks.
    -this is due to the unfortunate rail-splitting capacitors in a half-bridge, which divide the input voltage by two.

    Also, the Half bridge needs these highly expensive , extremely low dissipation factor, rail-splitting film capacitors.....these are more expensive than a the extra mosfets in a full bridge, would be payed for by the fact that the full bridge doesn't need the expensive film capacitors.

    4 FETs, Two NCP5181 Bootstrap fet drivers.

    2 FETs, one NCP5181 Bootstrap fet driver, 2 Pulse rated film capacitors

    ...Already the half-bridge is looking awry...........but there's more woes for it........

    the half bridge cannot utilise low-side resistive current sensing, because when the high side fet conducts...most of the power current would not go through the low-side current sense the half-bridge must use an expensive current sense transformer in order to be able to sense any primary overcurrents.

    ..the Full-Bridge can just use a cheap current sense resistor.

    Also, in the event of overload, the half-bridge's rail-splitting capacitors will end up with one discharged , and the other charged all the way up to the rail........which means that each rail-splitting capacitor must be rated for the full Vin of the DC thats two, expensive 400V rated pulse capacitors for the half bridge.

    Also, the film capacitors for the half-bridge take up a large amount of space in the half bridge.

    Is anyone seriously going to defend the half-bridge?

    Even more woes for the half-bridge in that it cannot do peak current mode control without blowing itself up, or at the very least running in an unstable way...this is mitigated by adding a balancing winding, but thats more expense and complexity.

    The full-bridge might need more heatsinks...but actually, no it won't...because if you use Insulated tab fets you can simply fix the four fets of a full bridge to the same heatsink, side-by-side.

    Its already been said that primary current is much higher for a half-bridge than a there's more woes for the half-bridge at the EMC testing stage.

    So, Is anyone seriously going to defend the Half-Bridge vs the Full-Bridge?...Surely not?
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