To increase the traffic rate in phosphor-LED visible light communication (VLC), a multi-band orthogonal frequency division multiplexed (OFDM) modulation is first proposed and demonstrated. In the measurement, we do not utilize optical blue filter to increase modulation bandwidth of phosphor-LED in the VLC system. In this proposed scheme, different bands of OFDM signals are applied to different LED chips in a LED lamp, this can avoid the power fading and nonlinearity issue by applying the same OFDM signal to all the LED chips in a LED lamp. Here, the maximum increase percentages of traffic rates are 41.1%, 17.8% and 17.8% under received illuminations of 200, 500 and 1000 Lux, respectively, when the proposed three-band OFDM modulation is used in the VLC system. In addition, the analysis and verification by experiments are also performed.

https://ir.nctu.edu.tw:443/bitstream/11536/124370/1/750899dc1ea5cf1c0c32707cf0ed1328.pdf

Utilization of multi-band OFDM modulation to increase traffic rate of phosphor-LED wireless VLC

Recent developments in improving lighting efficiency and cost reduction of LEDs have made them suitable alternatives to the current lighting systems. In this paper, a novel offline structure is proposed to drive LEDs. The proposed circuit has a high-input power factor, high efficiency, a long lifetime, and it produces no flicker. To increase the lifetime of the converter, the proposed circuit does not include any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode flyback converter in order to improve power factor. Additionally, a buck converter is added to the third winding of the flyback transformer in order to create two parallel paths for the electrical power to feed the output load. DC power reaches the load through one stage (flyback) and ac power reaches the load through two stages of conversion (flyback + buck). Therefore, in the proposed one-and-a-half stage circuit, the efficiency is improved compared to a regular two-stage circuit. Although the proposed structure has some output current ripple, it is low enough (less than 8%) that the structure can be rendered flicker free, as shall be discussed. Principles of operation and design equations are presented as well as experimental results for a 700 mA/20 W universal input prototype.

Flicker-Free Electrolytic Capacitor-Less Universal Input Offline LED Driver With PFC

Provided is an LED driving apparatus. The LED driving apparatus includes a plurality of LED groups each comprising one or more diodes, a switch group comprising a plurality of switch units connected respectively to the LED groups to drive the connected LED group when a control signal is activated, and a switch controlling unit configured to compare an input voltage of the LED groups with an output voltage of the LED groups, calculate a comparison value, and generate the control signal according to the comparison value. Accordingly, the LED driving apparatus drives the LED groups selectively according to the difference between the input voltage of the LED group and the output voltage of the LED group, thereby overcoming the problem of heat generation by forward voltage distribution.

Light emitting diode driving apparatus

Light-emitting diodes (LEDs) are coming strongly into the lighting market due to their advantages over conventional lighting solutions: energy efficient, controllable in both light and color, long lifetime, lack of a warm-up period, and high power density. Some of these advantages will make LED light sources to be more than just a light bulb, being able to transmit data, control light color, hue, and intensity or even detect people in indoor environments. Nevertheless, these advantages attributed to LED capabilities are, in reality, achieved thanks to the LED driver. This paper reviews the current state-of-the-art strategies to drive LEDs from ac power grids with special emphasis into removing the most limiting component from the point of view of the lifetime, which is the electrolytic capacitor, while achieving a flicker-free performance of the light output of the LED driver. Moreover, it focuses on analyzing the required regulations, challenges, and applicability of LED drivers in both single-phase and three-phase ac power grids.

/pdf/a-review-on-flicker-free-ac-dc-led-drivers-for-single-phase-4we7qsxypf.pdf

A Review on Flicker-Free AC–DC LED Drivers for Single-Phase and Three-Phase AC Power Grids

A simple, efficient, and low-cost quasi-resonant LED driver is presented. The proposed driver relies on capacitive safety isolation barrier and eliminates the need for a bulky isolation transformer. Thus, cost and footprint area can be reduced. This paper describes the topology and presents the theory of operation. Theoretical predictions are verified by simulation and experimental results.

/pdf/quasi-resonant-led-driver-with-capacitive-isolation-and-high-549k4rdnp5.pdf

Quasi-Resonant LED Driver With Capacitive Isolation and High PF

This paper presents a noble AC/DC converter-free LED driver for LED lighting applications. The presented LED driver applies the AC mains power directly to the LED strings with no AC/DC converter stage, thus bulky transformer and life-time limiting electrolytic capacitor no longer needed. This small-sized, low-cost and reliable LED lighting driver was realized with an LED driver IC, which selectively empowers multi-channel LED strings based on the measured input AC voltage signal. The IC was fabricated in 1-um high voltage BCD process capable of handling AC input voltage up to 240 V. By PWM-controlling the LED-driving high-voltage switches, the IC resolved the thermal issue which is critical for the reliability of LED lighting module. A 4-W prototype LED driver module was implemented and tested to verify the feasibility of the suggested Converter-/Capacitor-less (ie. CC-less) LED driver scheme for low cost LED lighting.

AC/DC converter free LED driver for lightings

Disclosed herein are a PWM control circuit, a flyback converter, and a PWM control method. The PWM control circuit includes: a peak storing and reference signal generating unit storing a peak value of one period of a feedback signal from a secondary side output and inverting the peak signal arid outputting the inverted peak signal as a reference signal; and a PWM control signal generating unit generating a PWM control signal by using an output obtained by comparing the reference signal with a reference waveform from the peak storing and reference signal generating unit. In addition, the flyback converter including the same and the method for controlling PWM are proposed.

PWM control circuit, flyback converter and method for controlling PWM

There is provided an apparatus for driving a light emitting diode (LED), capable of distributing current stress applied to the LED. The apparatus includes an LED part including a plurality of LED units respectively including at least one LED, the plurality of LED units being connected in parallel to a power input terminal to which rectified power in sine wave form is supplied, and, among the plurality of LED units connected in parallel, a termination end of the LED unit in a front end being connected to a middle of an adjacent LED unit; and a current source unit including a plurality of current sources respectively connected to termination ends of the plurality of LED units and allowing corresponding current to flow through the plurality of LED units.

Apparatus for driving light emitting diode

There is provided a light emitting diode (LED) driver having an offset voltage compensating function compensating for an offset voltage generated at the time of driving of an LED, the LED driver including: a driving unit detecting a current flowing in an LED unit having at least one LED, as a voltage and controlling the current flowing in the LED unit according to a comparison result between the detected voltage and a reference voltage having a preset voltage level; and an offset compensating unit integrating a voltage difference between the detected voltage and the reference voltage and adding or subtracting a compensating current according to an integration result to thereby compensate for an offset.

Light emitting diode driver having offset voltage compensating function

PURPOSE: A light emitting diodes driver having a compensatory function for off-set is provided to compensate for the offset voltage by using a transconductance amplifier and integrating circuit and to improve the reliability of a driving LED. CONSTITUTION: A driver(110) detects the voltage of a light emitting diode portion. The driver controls current by comparing a reference voltage with a detected voltage. An offset correction part(120) integrates the voltage difference between the reference voltage and the detected voltage. An offset correction part corrects offset by using the integral result. The offset correction part comprises an integrator and an amplifier.

Jae Shin Lee

Papers

AC/DC converter free LED driver for lightings

PWM control circuit, flyback converter and method for controlling PWM

Apparatus for driving light emitting diode

Light emitting diode driver having offset voltage compensating function

Light emitting diodes driver having funciotn off-set voltage