M. Rico-Secades

A Universal-Input Single-Stag2e High-Power-Factor Power Supply for HB-LEDs Based on Integrated Buck–Flyback Converter

Due to the high rise in luminous efficiency that high-brightness light-emitting diodes (HB-LEDs) have experienced in recent years, many new applications have been researched. This paper covers a streetlight LED application using the offline integrated buck-flyback converter (IBFC) developed in previous works. In this application, the converter is used to provide power-factor correction from a universal ac source. A control loop using the LM3524 IC has been implemented for testing the feasibility of Enabling pulsewidth modulation dimming mode. First, the LED load has been linearized and modeled in order to calculate the IBFC topology properly. Second, the converter has been designed and tested at the laboratory. The converter has also been modeled in order to design a fixed-frequency constant-current control. The dynamics of all the stages involved in the closed loop have been taken into account in order to develop an adequate controller. Finally, the experimental results obtained from the laboratory tests are discussed.

A Universal-Input Single-Stage High-Power-Factor Power Supply for HB-LEDs Based on Integrated Buck-Flyback Converter

Due to the high rise in luminous efficiency that HB-LEDs have experienced in the last recent years, many new applications have been researched. In this paper, a streetlight LED application will be covered, using the Integrated Buck-Flyback Converter developed in previous works, which performs power factor correction (PFC) from a universal ac source, as well as a control loop using the LM3524 IC, which allows PWM dimming operation mode. Firstly, the LED load will be linearized and modeled in order to calculate the IBFC topology properly. Afterwards, the converter will be calculated, presenting the one built in the lab. Secondly, the converter will be modeled in order to build the closed loop system, modeling the current sensor as well in order to develop an adequate controller. Finally, experimental results obtained from the lab tests will be presented.

PWM Series Dimming for Slow-Dynamics HPF LED Drivers: the High-Frequency Approach

This paper deals with the capability of pulse width modulation (PWM) dimming operation added to the high-power factor-integrated buck-flyback converter (IBFC), which was developed in previous works for LED lighting applications. First, the two main dimming techniques will be introduced, namely, analog dimming and PWM dimming. Then, the three main PWM dimming schemes found in the literature, that is, enable dimming, series dimming, and parallel dimming, will be briefly discussed. Afterwards, the IBFC topology will be tested performing both analog and enable dimming. In addition, a new proposal is introduced: the high-frequency series PWM dimming technique, which overcomes all the challenges faced when developing PWM dimming capabilities in low slew-rate constant-current fixed-frequency-controlled converters and offers all the advantages of PWM dimming over analog dimming while maintaining good efficiency. The proposed dimming-technique control loop, as well as the laboratory tests, will be presented, discussed, and compared to analog dimming and PWM dimming, showing satisfactory results in terms of dimming ratio, input current total harmonic distortion (THDI), and power factor.

Investigation of a New Control Strategy for Electronic Ballasts Based on Variable Inductor

In this paper, a new control method for electronic ballasts based on the use of a variable inductor is presented. The main goal is to perform the complete control of the electronic ballast by maintaining the switching frequency constant and without using other parameters of the power converter, such as input voltage or duty cycle. The magnetic regulator is controlled by means of a dc current, which allows performing both lamp soft starting and lamp dimming. Apart from the important advantage of keeping a constant frequency during full electronic ballast operation, the proposed method presents additional advantages when compared to other control methods, such as inherent isolated control, more linear control characteristics, constant electrode power, and higher efficiency. Experimental results from a 36-W linear fluorescent lamp prototype are presented.

Single-stage constant-wattage high-power-factor electronic ballast with dimming capability

A novel single-stage high-power-factor electronic ballast is presented in this paper. The ballast is obtained from the integration of a buck-boost converter and a half-bridge LC resonant inverter. The ballast features lamp power regulation against line voltage fluctuations together with high power factor and dimming capability. The steady-state analysis of the ballast is performed and a low-frequency model of the input stage is derived. A design example, including closed-loop circuitry, is also presented. Finally some experimental results from a lab prototype are shown.

Dimming of High-Brightness LEDs by Means of Luminous Flux Thermal Estimation

Usually, pulsewidth modulation (PWM) operation is selected as the best dimming strategy to drive high-brightness LEDs. Nevertheless, to obtain an enhanced full linear dimming control of the device, the luminous flux should be measured. This paper proposes a control method based on an estimator of the luminous flux emitted by the LED. Based on the characterization of the LEDs, this estimator is defined. The estimator provides the flux value from only two temperature values (the case temperature and the ambient temperature). Once the estimator is validated, the electronic driver to supply the LEDs, as well as the digital control scheme, are presented. Such a control scheme is suitable for both AM and PWM dimming strategies. A prototype of the electronic driver has been built and tested, and experimental measurements of AM and PWM dimming are presented. It can be concluded that with the proposed estimator, the flux emitted by the LEDs can be accurately estimated. Thus, the output light control of the LEDs can be accomplished by sensing temperature rather than luminous flux. The final output characteristic of the system shows linearity between the output flux and the reference value, with AM as well as with PWM dimming of the LEDs.

Evaluation of a low-cost permanent emergency lighting system based on high-efficiency LEDs

Nowadays, Permanent Emergency Lighting Systems (PELSs) are widely used in many applications, including emergency exit indication and lighting in critical or strategic points. Limitation in operation hours in classical lamps (10 000-20 000 h for fluorescent lamps) implies short lamp replacement times and, therefore, high maintenance costs. This paper shows an alternative solution based on high-efficiency LEDs. The long operation life (above 100 000 h) of high-efficiency LEDs with a very simple electronics circuitry implies an interesting solution for these types of applications. A 30-lm and 1-h PELS has been built and tested. A low-cost power supply has been built and used as a battery charger and LED driver.

Low cost electronic ballast for a 36-W fluorescent lamp based on a current-mode-controlled boost inverter for a 120-V DC bus power distribution

A non-resonant electronic ballast based on one power switch and on one reactive element-one inductance-is described in this paper. The special current mode control implementation provides an intrinsic short-circuit protection and a very simple control circuitry. Filament heating time, current during the heating period, and protection against broken tube can be easily implemented with the proposed circuitry. A greenhouse application with a 120-V dc bus power distribution is presented in this paper. The dc bus voltage is easily obtained (in this particular application) from a classical series-connected 12-pulse rectifier in combination with a transformer with two secondary windings (one in Wye connection and other one in Delta connection). An additional advantage of this configuration is the high power factor obtained at the input stage.

Analysis and design of a novel single-stage high-power-factor electronic ballast based on integrated buck half-bridge resonant inverter

A novel single-stage high-power-factor electronic ballast obtained from the integration of a buck DC-to-DC converter and a half-bridge resonant inverter is analyzed in this paper. The buck converter is operated in discontinuous conduction mode and at constant frequency providing an input power factor high enough to satisfy present standard requirements. The operation of the proposed ballast is also investigated in detail in this paper, obtaining the important equations and characteristics in order to allow interested readers to perform an easy design. A ballast prototype supplying two 36 W fluorescent lamps has been both simulated and implemented at the laboratory. The results predict good market possibilities for the proposed topology in terms of reliability, cost, efficiency, and lamp life.

Analysis and experimental results of a single-stage high-power-factor electronic ballast based on flyback converter

A new single-stage high-power-factor electronic ballast based on a flyback converter is presented in this paper. The ballast is able to supply a fluorescent lamp assuring a high-input power factor for the utility line. Other features are lamp power regulation against line voltage variations and low lamp current crest factor, both assuring long lamp life. The ballast is analyzed at steady-state operation, and design equations and characteristics are obtained. Also, a procedure for the ballast design is presented. Finally, simulation and experimental results from a laboratory prototype are shown.