1.6-kW GaN-Based 1-MHz CrM Totem-Pole PFC Reference Design

High-frequency, critical-conduction-mode (CrM), totem-pole power factor correction (PFC) is a simple approach for designing high-density power solutions using GaN. This reference design uses a 600-V GaN power stage, the LMG3410, from Texas Instruments (TI) and TI's Piccolo™ F280049 controller.

This high-density (165 × 84 × 40 mm) two-stage interleaved 1.6-kW design is suited for many space-constrained applications, such as servers, telecom, and industrial power supplies.

All of these systems require a front-end power factor correction (PFC) circuit to shape the input current of the power supply, so as to meet the power factor and current total harmonic distortion (THD) norms defined in IEC61000-2-3.

Interleaving of the power stages reduces input and output ripple currents. In this design, the PFC circuit shapes the input current of the power supply to be in phase with the mains voltage, and helps maximize the real power drawn from the mains.

The PFC front end also offers several benefits, which include the reduction in input root mean square (RMS) current, facilitation of hold-up during brief power interruptions, improvement of efficiency of downstream converters, and reduction of current stresses in neutral conductors in Y-connected three-phase systems.

Requirements for PFC front ends have undergone considerable changes over the last few years due to increasing demands for smaller size and higher efficiency. The challenge to meet premium levels of 80 plus standards calls for very-high efficiency over wide operating ranges of input and output. This need for high efficiency has generated considerable interest in bridgeless topologies for the PFC stage that can push the efficiency above 99%.

Block diagram of 1.6-kW PFC regulator (click on image to enlarge)

Because of the need for both smaller size and higher efficiency, simpler topologies that use fewer components and are capable of switching at higher frequencies are the current requirement in the PFC front end. The adoption of topologies using GaN power devices is relevant in this context.

The GaN power stage allows the implementation of bridgeless totem-pole topologies for PFC, which would be difficult to implement using silicon MOSFETs. The transition mode operation of the totem-pole power stage, when extended to zero voltage switching, lets the switching frequency increase into the MHz range.

This reference design is an attempt to meet the above challenges of telecom, server, and industrial power supplies. This design uses the fast switching capability of the driver-integrated GaN field-effect transistor (FET) from TI (LMG3410) and the advanced features of TI's C2000™ Piccolo™ TMS320F280049 microcontroller (MCU) to realize a totem-pole PFC with fast switching (up to 1 MHz) and zero-voltage switching-on (ZVS) transition capability.

Two-channel interleaving is used to demonstrate the design's capability to cater to higher power applications by adding parallel interleaved power stages. High efficiency of above 99% is demonstrated, though it is possible to further improve it by optimizing the design of the magnetics. The design can meet the power factor (PF) and current THD requirements applicable to the systems addressed.

The main features of this reference design are the high switching frequency (made possible due to the LMG3410 GaN power switches), ZVS operation (made easier by the advanced features of F280049), bridgeless transition-mode totem-pole operation, and interleaving the transition mode operation.

Features of this reference design include:

• Compact power stage of size 65 × 40 × 40 mm with power density of greater than 250 W/in3
• High efficiency of 98.7% at full load and 230-Vac input
• TI's LMG3410 GaN power stage with integrated driver and protection ensures circuit reliability and eases design
• Full digital control using TI's Piccolo™ F280049 controller
• Wide operating input range of 85- to 265-Vac
• Power factor greater than 0.99 and low THD
• Meets current THD regulations as per IEC 61000-3-2
• Protects for output overcurrent, overvoltage, and undervoltage conditions
• External cooling not required
• Operation up to 55°C ambient for loads ≤800W
• Built-in 10-W supply for housekeeping power needs and system fan driving