Paul L. Brohlin

High efficiency and power density GaN-based LED driver

LED lighting is becoming more attractive and popular due to its high efficiency, long lifetime, instant brightness and ability to dim. But LEDs are powered by DC, which requires a rectifier to allow it to run off the AC utility grid. These converters must have small form factors and operate in high ambient temperatures due to the close proximity of the LED light. Gallium Nitride (GaN) based switched mode power supplies have the ability to increase switching frequencies to allow for form factors small enough to enable new applications with stricter space requirements. But to achieve this size reduction, the switching frequency must operate in the megahertz range, which requires soft switching techniques to achieve acceptable performance. A small and simple analog hysteresis-controlled valley-switched floating buck converter is proposed to solve these problems. This solution has a minimal component count while maintaining similar performance to existing solutions. A 20W prototype is built to verify the performance of the converter, which is measured to have a size reduction of 1.87× of the power stage when compared to an existing commercial product while achieving an efficiency of 91.2%, an input current THD of 15.9% and PF of 0.976.

Design and magnetics optimization of LLC resonant converter with GaN

This paper presents the design and magnetics optimization of 1-kW regulated LLC resonant converter with GaN FETs. By adopting the GaN FETs for primary side switches, the gate driver loss and turn-off loss are significantly reduced. A new structure of integrated transformer with stacked planar cores, shaped windings and synchronous rectifier MOSFET proposed to reduce the core loss and winding loss. The proposed integrated transformer has highly compact structure including transformer, resonant inductor, SR MOSFET and output capacitor. A regulated 1-kW LLC resonant converter prototype is designed and tested. The peak efficiency can reach 97.4%.

Challenges in reliably driving GaN devices

GaNs properties of low Coss, Crss, and lack of reverse recovery make it a more efficient power switch versus silicon. These characteristics enable higher-frequency hard-switched topologies such as totem-pole bridgeless power factor converter (PFC) that cannot be realized by silicon MOSFETs and insulated-gate bipolar transistors (IGBTs) due to their high switching losses. To take advantages of these properties, GaN must be switched quickly and reliably. This paper examines requirements for the driver, package, and the GaN HEMT to enable efficient and reliable switching.