Abstract-Various AC/DC LED driver topologies have been proposed to meet the challenges of achieving a compact, efficient, low-cost and robust multi-string LED lighting system. These LED drivers typically employ a two-stage topology to realize the functions of AC/DC rectification and independent current control of each LED string. The choice of having two stage conversions involves additional hardware components and a more complicated controller design process. Such two-stage topologies suffer from a higher system cost, increased power loss, and large form factor. In this paper, a single-stage AC/DC single-inductor multiple-output (SIMO) LED driver is proposed. It uses only one single inductor and N+1 active power switches (N being the number of LED strings) with reduced component count and smaller form factor. The proposed driver can achieve both functions of AC/DC rectification with a high power factor and precise independent current control of each individual LED string simultaneously. A prototype of an AC/DC single-inductor triple-output (SITO) LED driver is constructed for verification. Experimental results corroborate that precise and independent current regulation of each individual LED string is achievable with the proposed driver. A power factor of above 0.99 and a peak efficiency of 89% at 30 W rated output power are attainable.
This paper proposes a closed-loop nonlinear method for precisely controlling the luminosity and correlated color temperature (CCT) of a bi-color adjustable light-emitting diode (LED) lamp. The objective is to achieve a precise and fully-independent dimming and CCT control of the light mixture emitted from a two-string LED lamp comprising warm-white and cool-white color LEDs, regardless of the operating conditions and throughout the long operating lifetime of the LED lamp. This control is formulated using the non-linear empirical LED model of the bi-color LED system. Experimental results show that with the proposed closedloop nonlinear control, both CCT and dimming control of the bi-color lamp is significantly more accurate and robust to ambient temperature variations, ambient light interference, and LED aging than the conventional linear control used in existing products. The maximum error in luminous flux employing the proposed nonlinear control method is 3%, compared with 20% using the closed-loop linear method. The maximum deviation in CCT is only 1.78%, compared with 27.5% with its linear counterpart.1 For future correspondence, please email: sctan@eee.hku.hk.
There has been growing interest in single-inductor 5 multiple-output (SIMO) dc-dc converters due to its reduced cost 6 and smaller form factor in comparison with using multiple single-7 output converters. An application for such a SIMO-based switch-8 ing converter is to drive multiple LED strings in a multichannel 9 LED display. This paper proposes a quasi-hysteretic finite-state-10 machine-based digitally controlled single-inductor dual-output 11 buck switching LED driver operating in discontinuous conduction 12 mode (DCM) and extends it to drive multiple outputs. Based on 13 the time-multiplexing control scheme in DCM, a theoretical upper 14 limit of the total number of outputs in a SIMO buck switching LED 15 driver for various backlight LED current values can be derived 16 analytically. The advantages of the proposed SIMO LED driver 17 include reducing the controller design complexity by eliminating 18 loop compensation, driving more LED strings without limited by 19 the maximum LED current rating, performing digital dimming 20 with no additional switches required, and optimization of local bus 21 voltage to compensate for variability of LED forward voltage V F 22 in each individual LED string with smaller power loss. Loosely 23 binned LEDs with larger V F variation can, therefore, be used for 24 reduced LED costs. 25 Index Terms-Boundary conduction mode (BCM), discontinu-26 ous conduction mode (DCM), finite-state machine (FSM), single-27 inductor dual-output (SIDO), single-inductor multiple-output 28 (SIMO). 29 I. INTRODUCTION 30 A N LED driver is essentially a current source (or sink) 31 which maintains a constant current required for achieving 32 the desired color and luminous flux from an array of LEDs. A 33 number of highly efficient switching LED drivers have been re-34 ported in the literature and their primary objective is to achieve 35 high power conversion efficiency [1]-[11]. Besides efficiency, 36 another important consideration is the scalability of the exist-37 ing single-inductor dual-output (SIDO) switching converter to 38 drive multiple independent LED strings in a single-inductor 39 multiple-output (SIMO) topology for reduced cost and smaller 40
In this paper, a straightforward plug-and-play voltage Ripple Mitigator (RM) is proposed. Unlike many existing voltage reduction methods, the proposed device can be attached to an DC link of a DC power grid or power electronics system WITHOUT MODIFYING THE HOST SYSTEM ITSELF. With the requirement for the DC-link voltage measurement only, this device can be directly plugged into the DC-link (i.e. being a plug-and-play module). It is suitable for the protection of DC utilities/systems and can also be used as a direct replacement of ripple-canceling electrolytic capacitor normally used in DC voltage links. Theoretical analysis and experimental work on a boost-type PFC rectification system have been successfully performed to validate the effectiveness of the ripple-mitigating function, the hot-swap operation and the non-intrusive property of the RM. Practical results obtained from a 110W miniature DC power system comprising an AC/DC converter and two resistive loads are included to demonstrate some of the functions of the RM. I.
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