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Summary of GaN-based MHz CRM Totem-pole PFC

Fig. 1. Prototype of interleaved 1.2kW MHz totem-pole PFC.
With the advent of 600V gallium-nitride (GaN) power semiconductor devices, the totem-pole bridgeless power factor correction (PFC) rectifier, which was a nearly abandoned topology, has suddenly become a popular solution for applications like front-end converters in the server and telecommunication power supplies. This is mostly attributed to the significant performance improvement of the GaN high-electron-mobility transistor (HEMT) as compared to the silicon (Si) metal - oxide - semiconductor field-effect transistor (MOSFET); particularly its better figure-of-merit and significantly smaller body diode reverse-recovery effect.

The cascode GaN HEMT is applied in the totem-pole PFC rectifier while pushing the operating frequency to above 1MHz. Several important issues, which are less significant at low frequencies, are emphasized at high frequencies, and corresponding solutions are proposed and experimentally verified.

In this research, the advantages of the totem-pole PFC rectifier are first summarized, while the differences between hard-switching and soft-switching and between the Si MOSFET and the GaN HEMT are then illustrated. After that, detailed design considerations are presented, including a ZVS extension to solve the problem of switching loss caused by non-ZVS valley switching; variable on-time control to improve the power factor, particularly the zero-crossing distortion caused by traditional constant on-time control; and interleaving control to cancel the input current ripple. The volume of the DM filter is reduced significantly by pushing the operating frequency to several MHz and the use of multi-phase interleaving.

A 1.2kW two phase interleaved totem-pole PFC prototype is demonstrated with 220W/in3 power density and 99% efficiency. All proposed functions with closed-loop control are implemented by a 120MHz MCU.


Fig. 2. Tested efficiency.
Fig. 3. MCU-based digital control implementation.
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