Two-channel Light-emitting Diode Research Articles

LED Current Balancing Scheme Using Current-Fed Quasi-Z-Source Converter

This article presents a novel two-channel light emitting diode (LED) current balancing method using current-fed (CF) quasi-Z-source (qZS) dc-dc converter. The proposed LED driver is simple in structure and requires minimal number of component counts. Currents flowing through the two LED strings are automatically balanced owing to charge (amp-sec) balance condition on capacitors in the CF-qZS network. Since current balancing is achieved automatically by passive components, current control of the proposed converter is very simple. In addition, the proposed circuit uses only one active switch and one diode. The operating principle and characteristics of the proposed two-channel LED driver are analyzed in detail. To verify validity of the proposed converter, 80 W prototype is built and tested.

A Bridgeless Electrolytic Capacitor-Free LED Driver Based on Series Resonant Converter With Constant Frequency Control

High-brightness light-emitting diode (LED) is next generation of green lighting. However, the bulky electrolytic capacitor is required to compensate the difference of pulsating power, thereby restricting the lifetime. Meanwhile, the existing drivers based on pulse frequency modulation (PFM) is bound to arouse heavy electromagnetic interference. In this paper, the series resonant converter based LED drive is proposed to overcome the shortcomings of electrolytic capacitor and PFM control. The proposed method is to attenuate the low frequency ripples delivered from the power factor correction (PFC) to LEDs; therefore, the capacitance is reduced for energy storage of offline LED drivers. On account of the adoption of the switching controlled capacitor (SCC), the constant frequency control is achieved by the regulations of the equivalent capacitance. Half-bridge switches are shared by the bridgeless PFC and the resonant unit, therefore, single-stage LED drive is realized with high efficiency. In addition, SCC is simultaneously shared for the upper and lower half-bridge to reduce the cost and improve the power density. Operating principle, design considerations, and performance comparisons are examined in detail. Finally, all the superior performances of proposed LED driver are verified by simulation and experimental prototypes with two-channel LEDs, and rated output power of 80 W.

Nonisolated Single-Switch Two-Channel LED Driver with Simple Lossless Snubber and Low-Voltage Stress

In two-channel light-emitting diode (LED) driver, capacitive-current-balancing method is the simplest and the most effective way to equally balance the current in each channel due to its simplicity. As a result, the capacitive balancing method was used with flyback or tapped-boost converters in low-power LED applications. Since flyback and tapped-boost converters suffer from a snubber loss and a high-voltage stress on the switching devices, conventional approaches use additional passive components, resulting in the limitations on the cost and power density. In this paper, a new converter topology for low-power two-channel LED application has been proposed. The proposed converter uses the blocking capacitor and the output capacitor as a snubber capacitor so that it has a low-voltage stress without using the additional components. Although the blocking capacitor plays a role as a snubber capacitor, the current balancing characteristic is still preserved. Furthermore, the proposed converter has a high efficiency since it minimizes the number of semiconductor components in the current paths. The effectiveness of the proposed converter has been verified with an offline 3.3 Vdc input and 11.55 W rated output prototype.

Input-Current-Ripple-Free Two-Channel LED Driver

In this paper, an input-current-ripple-free two-channel light-emitting diode (LED) driver is presented. In the proposed LED driver, a current-sharing capacitor is integrated into the boost converter to achieve the current-sharing among the LEDs and to enhance the output voltage gain. Moreover, an input current ripple cancellation circuit is employed to eliminate the input current ripple. Finally, the operating principle, analysis, and experimental results are provided to verify the effectiveness of the proposed LED driver.

Single-Switch Coupled-Inductor-Based Two-Channel LED Driver With a Passive Regenerative Snubber

In this paper, a single-switch coupled-inductor-based two-channel light-emitting diode (LED) driver with a passive regenerative snubber is presented. In the proposed LED driver, the energy-transferring capacitor is not only used to step up the voltage gain but also to achieve the current balance among LED strings. Moreover, a passive regenerative snubber is added not only to recycle the leakage inductance energy but also to improve the voltage gain. As compared with the prior work, only one switch is required. Thus, the configuration of the proposed LED driver is simpler. Since the proposed LED driver has a higher voltage gain than the prior work, the turns ratio of the proposed LED driver can be lower. Thus, the magnetic core size can be reduced. In addition, both LED drivers have the same component count. Finally, the operating principle, analysis, and experimental results are provided to verify the effectiveness of the proposed LED driver.

Duty-Ratio-Control-Aided LLC Converter for Current Balancing of Two-Channel LED Driver

Duty-ratio-control-aided LLC converter for current balancing of two-channel light-emitting diode (LED) driver is proposed and analyzed. Conventional current-balancing methods have the limitation on the power density and losses from additional components. With the aid of duty ratio control of an LLC converter, the proposed driver does not require any additional component. The total output current is controlled with the frequency modulation, and the duty ratio control is added to obtain current balancing of each LED channel. The advantage of the proposed method is the high power density and high efficiency. Also, it does not affect design procedure of a conventional LLC converter. The prototype of two-channel LED driver with 400-V input and 150–100-V/0.3-A output for each channel verifies the effectiveness of the proposed driver.

Nonisolated Two-Channel LED Driver With Automatic Current Balance and Zero-Voltage Switching

In this paper, a nonisolated two-channel light-emitting diode (LED) driver with automatic current balance and zero-voltage switching (ZVS) is presented. In this LED driver, a dc-blocking capacitor is connected with one side of the coupled inductor. Therefore, based on the ampere–second balance, a current source is generated with the average value of the positive current identical to the absolute average value of the negative current. Accordingly, the LED currents can be balanced naturally without extra active components or current sharing transformer. Consequently, the circuit components can keep at a low count. In addition, the proposed LED driver can achieve ZVS turn-on. Thus, the switching loss can be decreased. Above all, the proposed two-channel LED driver can be extended to a multichannel LED driver. In this paper, detailed theoretical analyses and experimental results are provided to verify the feasibility and effectiveness of the proposed LED driver.

Light‐emitting diode driver with a combined energy transfer inductor for current balancing control

This study proposes a two-channel light-emitting diode (LED) backlight driver specifically for liquid crystal display monitor application that utilises an integrated magnetic component: a combined energy transfer inductor for current balancing. The integrated magnetic component has two functions: as a boost inductor and as a differential-mode current balance transformer. Under proper design and arrangement, all of the windings are wound on a single UU-core. This scheme uses leakage inductance as boost inductor for energy transfer and mutual inductance as differential mode transformer for output current balancing. By introducing the magnetic component, power density is increased whereas the overall cost and volume of the magnetic components are reduced in comparison with those values under conventional topology. The operating principles and design considerations of the proposed LED driver were analysed. A 10 W prototype converter with a two-channel LED string was developed to verify the feasibility of the proposed driver. Experimental results show that the proposed LED driver provides an equal current for a two-channel LED string.

Embedded Temperature Sensor for Multilevel Current LED Driver

In this paper, we propose an embedded temperature sensor for the control of light emitting diode (LED) driving current, providing linear sensing, in which the output of the analog voltage corresponds to the current temperature. Sensing levels are truncated to four regions: 1) 120°C; 2) 140°C; 3) 160°C; and 4) 180°C. Thus, an increase in temperature is met with a corresponding drop in driving current to avoid burning the chip. A test chip was fabricated in using the TSMC 0.25-um CMOS process based on high-voltage mixed signals, in which two-channel LED drivers were embedded with two temperature sensors. The chip proved highly effective in all tests.