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PMP40766: Why are the same-named terminals of transformer T1 in LLC opposite between the primary and secondary sides?

Genius 11550 points
Part Number: PMP40766


Tool/software:

Hi ,

  Generally speaking, the dotted terminals (polarity markings) of the transformer in a half-bridge LLC converter are typically the same for both primary and secondary windings. However, in this specific design, the transformer T1 in the LLC converter has opposite dotted terminal configurations between the primary and secondary sides, which resembles the transformer setup in a flyback converter. As shown in the figures, the first diagram represents a conventional half-bridge LLC transformer, while the second diagram depicts transformer T1 used in this solution. I'm having trouble understanding this difference and would appreciate an explanation.

Thanks,

  • Hi Links,

    A half bridge LLC is a double-ended topology where power is transferred to the output twice every switching cycle. It is not a single-ended topology like flyback where power is only transferred when the primary FET is off. Due to this, the dot orientation will only matter as to which of the secondary rectifiers is on. 

    Best Regards,

    Ben Lough