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UCC256301: AC Input Specifications

user1932012
Intellectual 750 points
Part Number: UCC256301

For the reason of the cost, the use of the UCC256301 in the case of not requiring a PFC is directly converted from the AC to the DC by the LCC.

What is the voltage range of the AC input in this case?

  • 0
    TI__Mastermind 40050 points
    Hello user1932012,

    Thank you for your interest in the UCC256301 LLC controller.

    The LLC converter is a DC to DC converter, where the input AC voltage is rectified to DC first, before the LLC transforms and regulates it to a different (usually lower) output voltage. The input DC is produced either by a PFC stage or by direct full-wave peak rectification (without PFC).

    LLC converters are popular due to their high efficiency, but this is true mainly for a narrow input range and a fixed output voltage. A wide-range input can be accommodated but at significantly reduced full load efficiency at the voltage extremes.

    To get the best performance from an LLC converter, it is preferable to keep the AC input range as narrow as possible. Remember that the rectified AC has a lower DC minimum valley voltage than the lowest AC peak voltage. That valley voltage must be included in the low-to-high input voltage range. It helps to limit non-PFC inputs to the usual low-line (90Vac-132Vac) or high-line (170Vac-264Vac) ranges. The traditional input voltage-doubler rectifier can be used to step a low-line source into the higher DC voltage range.

    Technically, 90Vac to 264Vac can be done (~80Vdc to 373Vdc after rectification), but your efficiency over line will be disappointing except at some nominal design point.

    By the way, I recommend to follow the datasheet design procedure because the UCC25630x Design Calculator Tool (SLUC634B) was developed on assumptions of narrow PFC input range, not for wide ranges of Vin or Vout. The controller can automatically handle a wider Vin range with decent efficiency under light load conditions when the PFC stage is often turned off, but not at full power.

    Regards,
    Ulrich