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Improving the Power Conversion Efficiency of Phase Shift Full Bridge Circuits – Introduction

2022.04.22

In recent years, power supplies for servers and on-board chargers have been required to deliver even higher power. Full bridge circuits are often used for such high-power power supplies, and in particular, phase shift full bridge (PSFB) circuits are capable of zero voltage switching (ZVS) operation when switching devices such as super junction MOSFETs (SJ MOSFETs) and IGBTs are turned on. Zero Voltage Switching (ZVS) operation is possible to reduce switching losses and thus handle higher power. However, as power supplies become more powerful, improving efficiency becomes a major issue. Generally, even if the efficiency is the same, the loss itself will be higher for high-power power supplies, so as high efficiency as possible is desirable.

The following sections of this chapter explain the necessity of a high-speed recovery type SJ MOSFET based on the circuit operation when an SJ MOSFET is used in a PSFB circuit. In addition, efficiency comparisons of SJ MOSFETs with different recovery characteristics will be performed to confirm the importance of recovery characteristics in PSFB circuits.

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