MTL Annual Research Report 2013

A 90.6%, 11-MHz, 22-W LED Driver using GaN FETs and a Burst Mode Controller

Figure 1: Block diagram of LED driver.

With the advent of reliable, high-brightness and high-efficacy LEDs, the lighting industry is expected to see a significant growth in the near future. However, for LEDs to completely replace the traditional incandescent and CFL bulbs, the power converters within the LED drivers need more efficiency and further miniaturization. Superior figure of merit (R_ds,ONxQ_g) of gallium nitride (GaN) FETs over silicon FETs can enable both high-efficiency and  high-frequency operation, thereby making power converters smaller, more efficient, and more reliable. Using integrated controllers and drivers can reduce the number of components on the driver PCB, further miniaturizing the driver. This work focuses on demonstrating a small form factor, high-efficiency offline LED driver using GaN FETs with an integrated gate driver and controller circuit implemented on a 0.35-mm CMOS process with 3.3V/15V voltage handling capability. Figure 1 shows the architecture of the LED driver implemented. The driver achieves a peak efficiency of 90.6% and a peak power factor of 0.96. In order to operate the converter efficiently at high frequencies, a Quasi-Resonant topology is employed. The resonant circuit, formed by L_RESO and C_OUT,GaN, helps achieve Zero Voltage Switching (ZVS). An on-chip integrated burst-mode controller is implemented to control the LED current, provide power factor correction, and drive the gate of the GaN FET.