Design of high performance LED drivers for smart and emotional lighting controls

Abstract

In Chapter 1, a phase-cut dimmable AC-DC buck LED driver is presented for electrolytic capacitor-less LED lighting applications. In the driver, the sine-reference band (SRB)-controlled average current technique is proposed to perform sine-average current control and phase-cut dimming control. The sine-average current control can regulate the average value of sine-wave LED current, maintaining a high power factor (PF) over a wide range of AC input voltage and output LED load. The phase-cut dimming control not only makes the LED driver compatible with two types of phase-cut dimmers, namely, leading-edge and trailing-edge dimming types, but also eliminates visible dimming flicker at the AC line frequency. Fabricated in a 0.35 $\mu$m CMOS process, experimental results show the line regulation of $\mu$ 0.014 %/V over 90 to 260 $V_{AC}$ and the load regulation of $\pm$ 0.008 %/V within the load range of 10 to 36 LEDs. The PF exceeds 0.95 under all conditions, and the peak efficiency of 90.7 % is achieved. The analysis of the flicker frequency verifies that the proposed dimmable LED driver completely eliminates visible flicker owing to the phase dimming variations without an output electrolytic capacitor. In Chapter 2, a single-transformer-winding multiple-output (STWMO) flyback LED driver is proposed for isolated offline RGBW lighting applications. For the current regulation of each individual LED string, the error-based switch control (EBSC) scheme and error-sum feedback circuit (ESFC) were implemented. According to the simulation results, the proposed STWMO LED driver can achieve excellent current regulation over a wide range of AC input voltages and minimize the current balance error for multi-channel LED currents. In addition, the proposed switched capacitor amplitude modulation (SCAM) dimming control scheme can independently adjust the LED current for each of LED strings without the current cross regulation problem.