song Li

Monolithically integrated drivers for eco-friendly LED system-on-a-chip applications

Monolithically integrated Light-Emitting Diode (LED) drivers greatly reduce the cost as well as enhance the reliability of LED system due to their reduction of bulky and expensive off-chip components and assembling cost. However, integrating all the passive and active components of an LED driver on chip is very challenging. This paper discusses current issues of designing a monolithically integrated LED driver and presents some considerations to these problems.

A 16–28-W 92.8%-Efficiency Monolithic Quasi-Resonant LED Driver With Constant-Duty-Ratio Frequency Regulator

This brief presents a monolithic high-voltage light-emitting diode (LED) driver for lighting applications. The LED driver is able to operate at high switching frequency because large switching loss is eliminated by zero-voltage switching. Inductor values are therefore reduced. A constant-duty-ratio frequency regulator (CDFR) is proposed to regulate the LED current, and the small signal characteristics of the proposed LED driver with CDFR are analyzed. The proposed design, including the controller and power transistor, was fabricated in MagnaChip 0.35-μm 700-V bipolar-CMOSLDMOS process. The LED driver with 2 × 3.9 μH inductors switches at around 5.4 MHz and powers up 16-28 1-W LEDs. Experimental results show that the LED driver achieves peak efficiency of 92.8% within the input voltage range of 55-120 V.

A 5.5W AC input converter-free LED driver with 82% low-frequency-flicker reduction, 88.2% efficiency and 0.92 power factor

This paper presents a 95VAC-120VAC mains powered converter-free LED driver for general lighting application. A quasi-constant power control scheme is proposed to significantly reduce the low-frequency-flicker, combined with a valley fill circuit to maintain good power factor performance. The driver achieves 88.2% efficiency and 0.92 PF with only 18% flicker at 110VAC 60Hz input and does not require any magnetics or electrolytic capacitors.

An AC Input Switching-Converter-Free LED Driver With Low-Frequency-Flicker Reduction

This paper presents a novel switching-converter-free ac–dc light-emitting diode (LED) driver with low-frequency-flicker reduction for general lighting applications. The proposed driving solution can minimize the system size as it enables the monolithic integration of the controller and power transistors while both the bulky off-chip electrolytic capacitors and magnetics are eliminated. Moreover, the driver can effectively reduce the harmful optical flicker at the double-line-frequency by employing a novel quasi-constant power control scheme while maintaining high efficiency and a good power factor (PF). The proposed driver is implemented with a single controller integrated circuit chip, which includes the controller and high-voltage power transistors, and the off-chip diode bridge and valley-fill circuit. The chip is fabricated with a 0.35-

22.8 An AC-input inductorless LED driver for visible-light-communication applications with 8Mb/s data-rate and 6.4% low-frequency flicker

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Low-Flicker Lighting From High-Voltage LEDs Driven by a Single Converter-Free Driver

120-V high-voltage CMOS process and occupies 1.85 mm2. The driver can provide up to 7.8-W power to the LED and achieves 87.6% peak efficiency and an over 0.925 PF with only 17.3% flicker from a 110-Vac 60-Hz input.

A multiple-string hybrid LED driver with 97% power efficiency and 0.996 power factor

Light-emitting diodes (LEDs) are becoming the dominant lighting source over their conventional counterparts. Besides the benefits of high efficiency and long lifetime, LEDs also show great potential for high-speed data transmission because of their wide bandwidth (BW). In addition to offering general lighting, the light output can be modulated with fast-switched LEDs to achieve visible light communication (VLC). Though over 100Mb/s data-rate has been demonstrated with white LEDs in the laboratory, the high-frequency modulation is hardly supported by commonly used dimmable drivers with switching converters to regulate LED current. In these drivers, the changing slope of LED current is limited by both low loop BW and large inductors and capacitors [1]. The linear multiple-string LED drivers [2], free of inductors and big capacitors, theoretically can provide higher turn on/off speed. However, the light output of these drivers usually varies significantly at the double-line-frequency, which not only is considered as a harmful optical flicker, but also greatly affects the effectiveness of data transmission. The linear driver in [3] regulates the product of LED current and LED voltage to mitigate the optical variation, but a multiplier has to be added in the regulation loop, resulting in limited BW.

A more accurate steady state analysis of zero-voltage switching quasi-resonant converters

This letter reports the design and characterization of high-power flip-chip high-voltage light-emitting diodes (HVLEDs), driven by a single converter-free LED driver for a compact and low-flicker lighting system. The HVLED chips show small forward voltage variation, uniform light emission, good optical output linearity, and stable thermal performance. All these characteristics well satisfy the demanding requirements of the novel quasi-constant power control scheme adopted in the converter-free LED driver. After bonding 12 HVLED chips (60 LED cells in total) and a single driver onto a silicon carrier through metal bonding, a low lighting flicker of 15.2%~17% was demonstrated, showing great potential for high-quality illumination applications that require low flicker, high light output, and good thermal stability.

Efficient use of uniform GaN HVLEDs for small-flicker general illumination applications with converter-free LED drivers

This paper presents a multiple-string hybrid LED driver powered by 100-120VAC input for general lighting applications. The proposed hybrid LED driver adaptively switches between Linear Mode and Switching Mode according to the input voltage to enhance the power efficiency. This work achieves 97% power efficiency and 0.996 power factor at 120VAC 60Hz input.

An AC powered converter-free LED driver with low flicker

A more accurate steady state analysis of the zero-voltage switching quasi-resonant (ZVSQR) converter is conducted in this paper. The conversion ratio equation and the conditions to achieve zero-voltage switching (ZVS) are derived. According to the analysis, a ZVSQR converter can be designed to operate within a wider input voltage range. A ZVSQR inverted buck converter is simulated as an example to verify the analytical results.