Kai-Jun Pai

Design and Implementation of RGB LED Drivers for LCD Backlight Modules

In this paper, a backlight module driver driving high-power red, green, and blue light-emitting diodes (RGB LEDs) for a 19-in liquid crystal display is proposed. The DC-DC series resonant converters (SRCs) with zero-voltage switching and constant-output-current control are implemented to drive the RGB LED arrays. Phase-shifted pulsewidth modulation dimming control is adopted to effectively narrow the load variations and improve the output voltage regulations of the SRCs. A DSP-based hysteresis control algorithm is performed to track the white-color point and the specified backlight luminance. Analysis and design considerations of the proposed drivers are presented in detail. Experimental results agree well with the theoretical predictions and confirm the validity of the proposed approach.

A Balancing Strategy and Implementation of Current Equalizer for High Power LED Backlighting

This paper presents a current equalizer to balance the driving currents for high power LEDs (light emitting diode). The proposed strategy combined PWM strategy and digital dimming control to achieve the same illumination for each driven diodes. To obtain the same average current, the duty cycle of LEDs is modulated according to its current amplitude instead of traditional current amplitude adjusting. Complete mathematical analysis and design considerations are detailed. The experimental results are close to the theoretical predictions, and the measured tolerance errors are all below 4%.

Feedback Design of a Piezoelectric Transformer-Based Half-Bridge Resonant CCFL Inverter

The feedback loop design of a half-bridge (HB) resonant inverter based on a piezoelectric transformer (PT) for driving a cold cathode fluorescent lamp (CCFL) is presented in this paper. In order to stabilize the CCFL driving current and luminance, the PT-based resonant inverter incorporating a feedback compensator is designed to track the operating frequency. The dynamic equations and the small-signal model of the presented inverter system are established by using the harmonic approximation and harmonic balance procedures. The feedback compensation is performed by applying the derived small-signal block diagram. The complete mathematical analysis and design considerations are presented in detail. The experimental results agree with the theoretical predictions and confirm the validity of the proposed design approach.

Digital-dimming controller with current spikes elimination technique for LCD backlight electronic ballast

A novel simple control method to improve the ignition behavior of cold cathode fluorescent lamp in digital-dimming mode is proposed in this paper. To extend the lamp life, we realize a digital-dimming controller with current spikes elimination technique (DDC-CSET) to reduce the high ignition voltage and to eliminate the ignition current spike. The half-bridge resonant inverter is employed in the presented backlight system to promote the system efficiency. Complete analysis and design considerations are discussed in detail in this paper. Experimental results are close to the theoretical prediction. The overall efficiency of the system achieved at the rated power is over 91%. The ignition voltage is reduced about 30% without any lamp current spike occurred under digital-dimming operation.

Achieving maximum-efficiency tracking control for backlight electronic ballast with phase-locked loop techniques

Single-stage electronic ballast with maximum-efficiency tracking is proposed in this paper. The original backlight system incorporates a phase-locked loop (PLL) as a feedback mechanism to promote the system efficiency and stability. To overcome the drawbacks of conventional electromagnetic transformer and miniaturize the backlight module, the piezoelectric transformer (PT) is adopted for driving the cold cathode fluorescent lamp. In addition, the PLL is used to track the optimal operating frequency of PT for achieving maximum output efficiency. The feedback parameter used in the presented system is the phase component instead of the lamp current amplitude utilized traditionally. Simple model and design procedures are both constructed by reasonable parameter simplification and combination schemes. Complete analysis and design considerations are discussed in detail in this paper. Experimental results are close to the theoretical prediction.

A High-Voltage Input Backlight Module Driver for Multi-Lamp LCD Panels

A high-voltage DC input backlight module driver for multi-lamp LCD panels is presented in this paper. The 400-V DC output of a power factor corrector (PFC) is directly coupled to a class-D resonant inverter. Thus the requirement of a buck converter conventionally adopted to provide a low input voltage for the DC/AC inverter is eliminated. Also a single transformer with multiple secondaries is utilized to drive multiple lamps. The proposed backlight module driver features less circuit components, a lower cost and a higher efficiency. Design considerations are discussed and design procedures are derived. Simulations and experimental results confirm with the theoretical analysis

Design and Analysis of a Piezoelectric Transformer-Based Half-Bridge Resonant Inverter for CCFL Backlight Modules

A half-bridge (HB) resonant inverter for driving a cold cathode fluorescent lamp (CCFL) backlight module with a piezoelectric transformer (PT) is analyzed in this paper. The resonant inductance of the HB inverter is expressed as a function of the load current, the load resistance the PT circuit parameters. Also, the trans-admittance of the PT-CCFL combination network is measured to track the resonant frequency of the PT which may be varied due to the temperature rise. The efficiency of the HB resonant inverter, the output power of the PT and the CCFL driving current are thus remained almost constant. Experiments show that the observed results match the theoretical analyses

Control strategy for eliminating the temperature effect of piezoelectric transformer in the backlight module

A novel control strategy for eliminating the temperature effect of piezoelectric transformer (PT) in the backlight module is proposed in this paper. To overcome the drawbacks of the conventional electromagnetic transformer and miniaturize the backlight module, the PT is adopted for driving the cold cathode fluorescent lamp. In addition, a phase-locked loop (PLL) is incorporated into the original backlight system as a feedback mechanism to track the optimal operating frequency of PT, such that the temperature effect of PT is eliminated, and hence the system efficiency and stability are promoted. The feedback parameter used in the presented system is the phase component instead of the traditionally employed lamp current amplitude. A simple model and design procedure are both constructed by reasonable parameter simplification and combination schemes. Complete analysis and design considerations are discussed in detail in this paper. Experimental results agree with the theoretical prediction.

An improved digital-dimming controller for back-light module applying frequency-shift technique

A novel simple control method to improve the ignition behavior of cold cathode fluorescent lamp in digital-dimming mode is proposed in this paper. The half-bridge resonant inverter is employed in the presented back-light system. To extend the lamp life, we realize a digital-dimming controller with frequency-shift technique (DDC-FST) to reduce the high ignition voltage and to eliminate the ignition current spike. Complete analysis and design considerations are discussed in detail in this paper. Simulation and experimental results are close to the theoretical prediction. The overall efficiency of the system achieved at the rated power is over 91%. The ignition voltage is reduced about 30% without any lamp current spike occurred under digital-dimming operation.

A high-input-voltage backlight module driver for multi-lamp LCD panels

A half-bridge (HB) resonant inverter for driving a backlight module with multiple cold cathode fluorescent lamps (CCFLs) is proposed. Conventionally, a backlight module driving inverter is designed to operate with a low-input DC voltage. Therefore, a buck converter is required to step down the high-output DC voltage of a power factor correction (PFC) pre-regulator. The circuit cost is high and the conversion efficiency is low. In this letter, a high-input-voltage HB resonant inverter with only one transformer is used to drive multiple lamps. Analysis and design considerations are discussed in detail. Simulations and experimental results are close to the theoretical prediction. Copyright