Abstract
The switching loss of the secondary side rectifiers in LLC resonant converters can have a noticeable impact on the overall efficiency of the complete power supply and constrain the upper limit of the optimum switching frequencies of the converter. Two are the main contributions to the switching loss in the secondary side rectifiers: on the one hand, the reverse recovery loss (Qrr), most noticeably while operating above the series resonant frequency; and on the other hand, the output capacitance (Coss) hysteresis loss, not previously reported elsewhere, but present in all the operating modes of the converter (under and above the series resonant frequency). In this paper, a new technique is proposed for the measurement of the switching losses in the rectifiers of the LLC and other isolated converters. Moreover, two new circuits are introduced for the isolation and measurement of the Coss hysteresis loss, which can be applied to both high-voltage and low-voltage semiconductor devices. Finally, the analysis is experimentally demonstrated, characterizing the switching loss of the rectifiers in a 3 kW LLC converter (410 V input to 50 V output). Furthermore, the Coss hysteresis loss of several high-voltage and low-voltage devices is experimentally verified in the newly proposed measurement circuits.
Highlights
A high-power off-line Power Supply Unit (PSU) normally comprises at least two stages: a front-end Power Factor Correction (PFC) and a back-end DCDC converter that provides isolation and a tight regulated output [1,2]
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Summary
A high-power off-line Power Supply Unit (PSU) normally comprises at least two stages: a front-end Power Factor Correction (PFC) and a back-end DCDC converter that provides isolation and a tight regulated output [1,2]. The main contributions to losses in the DCDC converter include the conduction, the auxiliary, the switching, the driving, and the core loss [3,4]. For every converter design there is an optimum switching frequency at which the overall sum of losses is at its minimum and the maximum efficiency is achieved. Resonant and quasi‐resonant converters aim to diminish or completely get rid of the Resonant and quasi-resonant converters aim to diminish or completely get rid of the switching loss contribution, i.e., soft‐switching the power semiconductor devices. This can switching loss contribution, i.e., soft-switching the power semiconductor devices.
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