M. S. Perdigao

Comparative Analysis and Experiments of Resonant Tanks for Magnetically Controlled Electronic Ballasts

This paper presents a comparative analysis and experiments of resonant tanks for magnetically controlled electronic ballasts, focusing on their behavior and performance when driving hot cathode fluorescent lamps. Four different resonant tanks are analyzed: LC, LCC, capacitive impedance inverter, and CLL. The analysis is performed using a 36-W fluorescent lamp, which has been previously tested and modeled experimentally. The lamp model is used to derive the dimming characteristics of the different resonant tanks when using the resonant inductance as a control parameter. Analysis and experiments showed that instabilities appear when the lamp power is decreased below a minimum value, which effectively limits the dimming range of the ballast. Nevertheless, the proposed control method can be used to control lamp power in an adequate range provided that the resonant tank should be selected and designed properly.

Comparative Analysis and Experiments of Resonant Tanks for Magnetically-Controlled Electronic Ballasts

This paper presents a comparative analysis and experiments of resonant tanks for magnetically-controlled electronic ballasts, focusing on their behavior and performance when driving hot cathode fluorescent lamps. Four different resonant tanks are analyzed: LC, LCC, capacitive impedance inverter, and CLL. The analysis is performed using a 36 W fluorescent lamp, which has been previously tested and modeled experimentally. The lamp model is used to derive the dimming characteristics of the different resonant tanks when using the resonant inductance as control parameter. Analysis and experiments showed that instabilities appear when the lamp power is decreased below a minimum value, what effectively limits the dimming range of the ballast. Nevertheless, the proposed control method can be used to control lamp power in an adequate range provided that the resonant tank should be selected and designed properly.

Effects of the Junction Temperature on the Dynamic Resistance of White LEDs

This paper deals with the thermal characteristics of the I-V curve of GaN-based white LEDs, focused on the variations of the dynamic resistance. The final goal of this study is to improve the static and dynamic operation of the LED driver within a wide range of temperature. Four LEDs from different manufacturers were chosen for this study. The first part of the paper shows the thermal characterization of the forward voltage at a given injected current. After that, the experimental data are fitted in order to calculate the junction temperature accurately. Then, a small-signal analysis where the LEDs are supplied with dc current and an ac perturbation superimposed at the operation point under variable junction temperature is covered. This analysis allows the dynamic resistance to be experimentally determined for a wide junction temperature range. Furthermore, the experimental data have been fitted in order to establish the relationship between junction temperature and dynamic resistance variation, so the dynamic resistance can be determined for a given operation point. Finally, an illustrative example is presented as a case study in order to analyze the implications of the dynamic resistance on the output current ripple and on the closed-loop operation of an LED driver. The experimental results confirm that the junction temperature shift induces a variation in the dynamic resistance, which might have a significant effect on the output current ripple and closed-loop performance in certain LED fixtures.

Using Magnetic Regulators for the Optimization of Universal Ballasts

Nowadays, there are few commercial types of ballasts that are able to control fluorescent lamps with different power ratings. One of the main issues is how to get optimum operation for each lamp in this condition. This paper tries to demonstrate how to accomplish this objective using a magnetic regulator, i.e., using a variable inductor. This variable inductor is controlled by a dc current delivered by a forward converter directly supplied from the ballast dc bus voltage. This control current allows changing the resonant tank and adapting it to the working parameters imposed by each lamp, ensuring near-resonance working conditions. Design criteria and practical verifications are included to confirm this new technique. Theoretical predictions are verified with the experimental results for three TLD Philips fluorescent lamps, from 18 to 58 W.

Two Flyback-Based Integrated Converters for the Implementation of LFSW Electronic Ballasts

In this paper a new configuration of the two-flyback-based high-power-factor electronic ballast is proposed. The ballast is aimed to supply high intensity discharge (HID) lamps with a low frequency square waveform (LFSW), so that acoustic resonance (AR) phenomenon can be avoided. The proposed topology is compared to a previously presented one, which integrated the two flyback converters in a different manner. Therefore, this paper is focused on the comparison of both configurations by analyzing voltage and current waveforms and components stress. The proposed electronic ballast presents a high efficiency with a reduced number of components and no over current stress in the shared switch, which improves its efficiency. Experimental results validate both integrated configurations, but demonstrate a higher efficiency for the new arrangement proposed in this paper.

A Review on Variable Inductors and Variable Transformers: Applications to Lighting Drivers

This paper presents a literature review on magnetically-controlled devices, variable inductors and variable transformers, and their applications in lighting gear. It describes the fundamentals and basic operating principle of such devices. Then, it focus on the review of specific techniques and circuits taking advantage of the presence of a controlled inductance value, by covering recent applications regarding discharge and solidstate lamp drivers.

Optimization of universal ballasts through magnetic regulators

Nowadays there are few commercial types of ballasts able to control fluorescent lamps with different power ratings. One of the main issues is how to get optimum operation for each lamp in this condition. This paper tries to demonstrate how to accomplish this objective using a magnetic regulator, i.e. using a variable inductor. This variable inductor is controlled by a dc current delivered by a forward converter directly supplied from the ballast dc bus voltage. This control current allows changing the resonant tank, adapting it to the working parameters imposed by each lamp, ensuring near resonance working conditions. Design criteria and practical verifications are included to confirm this new technique. Theoretical predictions are verified with the experimental results for three TLD Philips fluorescent lamps, from 18 W to 58 W.

Magnetically Controlled Electronic Ballasts With Isolated Output: The Variable Transformer Solution

In this paper, the variable transformer solution is presented as a step forward in magnetically controlled electronic ballasts. The proposed technique takes advantage of the devices equivalent series inductance to provide a new flexible way for lamps luminous flux regulation. Output electrical isolation and constant frequency operation are also guaranteed by the proposed realization. A simple method for large-signal characterization of the variable transformer is described. An FH 14W/840 Osram lamp was chosen to validate this new technique and experimental results clearly show its adequate behavior.

A new technique to equalize branch currents in multiarray LED lamps based on variable inductor

In this paper, a new technique to equalize light-emitting diode (LED) currents in multiarray LED lamps is proposed. The current through the LEDs is controlled by changing the inductance of a variable inductor. The proposed technique can be employed to control the current through each LED branch independently. The operation principle of this technique and a design example of the proposed system are presented in detail in this paper. As an example, a forward converter has been selected to supply the LED branches, which can be designed to operate with one or several outputs. The component values of the converter as well as the LED current control circuit are also calculated as a design example. A prototype of the circuit has been implemented. The experimental results obtained at the laboratory are satisfactory and in accordance to the proposed design methodology. The proposed technique can prove to be very cost-effective for LED drivers in the range of 100 W and beyond with multiple independent LED arrays.

A variable inductor MATLAB/Simulink behavioral model for application in magnetically-controlled electronic ballasts

In magnetically-controlled electronic ballasts, in order to perform the lamp start and dimming, the typical resonant inductor is substituted by a variable inductor. This variable inductor is controlled by a dc current, which modifies the resonant tank in order to vary the rms value of the lamp current and thereby the luminous output. In order to perform optimization studies, computational models, which accurately simulate the real behavior of the fluorescent lamp and the variable inductor, in magnetically-controlled electronic ballasts, are extremely necessary. Traditionally, they are implemented in circuit-simulation programs, such as SPICE-based programs. In this paper it is demonstrated how a MATLAB/Simulink compatible behavioral model of a variable inductor can be developed easily using simple laboratory measurements. The resulting model includes coil losses but not temperature effects. Design criteria and practical verifications are included to confirm this model. Theoretical predictions are verified with the experimental results for a 36 W TLD Philips fluorescent lamp which has also been previously tested and modeled experimentally, in order to derive the dimming characteristics.