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Evaluation of GaN-Based MHz Interleaved CRM PFC Converter

Fig. 1. Operating frequency of CRMPFC in half-line cycle under different input volt-ages and different output power.
The critical conduction mode (CRM) boost power factor correction (PFC) converter is widely used in off-line power supplies due to its merits of zero-current switching (ZCS) turn-off of the diode and zero-voltage switching (ZVS), or valley switching, turn-on of the main switch. By interleaving two CRM boost PFC converters, the ripple of the input and output currents and the size of the input differential mode (DM) electromagnetic interference (EMI) filter can be reduced significantly, while the power rating can be extended to a higher level. Furthermore, a phase-shedding strategy can be used to improve the light-load efficiency.

With the advent of the 600V gallium nitride (GaN) high-electron-mobility transistor (HEMT), the converter's switching frequency can be pushed to several MHz. This is a dramatic improve-ment compared to the high-frequency capability of a silicon (Si) based power semiconductor devices. Previous research has demonstrated that the switching loss is the dominant loss in MHz frequency hard-switching conditions, and soft-switching is still critical to achieving high efficiency for the high-voltage GaN HEMT.

Combining the merits of the CRM PFC converter and the high-voltage GaN HEMT, a 1.2kW 1-3MHz GaN-based dual-phase interleaved CRM boost PFC converter is demonstrated to have 97.3% full-load efficiency and 120W/in3 power density. By pushing the frequency above 1 MHz, the benefit for EMI filter design is significant. As the required corner frequency of the EMI filter reaches hundreds of kHz, dramatic size and weight reduction can be projected. Finally, the CRM boost PFC has the limitation that the rectifier conduction loss and non-ZVS switching loss are dominant, especially in the MHz frequency range. The totem-pole bridgeless PFC converter is a promising solution to further improve efficiency by full-line ZVS extension strategy.

Fig. 2. Prototype and experimental waveforms of dual-phase interleaved CRM PFC converter under full-load conditions.
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