J. Cardesin

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.

Analysis, design and experimentation of a high voltage power supply for ozone generation based on the current-fed parallel-resonant push-pull inverter

The use of supply frequencies above 50-60 Hz allows for an increase in the power density applied to the ozonizer electrode surface and an increase in ozone production for a given surface area, while decreasing the necessary peak voltage. Parallel-resonant converters are well suited for supplying the high capacitive load of ozonizers. Therefore, in this paper the current-fed parallel-resonant push-pull inverter is proposed as a good option to implement high-voltage high-frequency power supplies for ozone generators. The proposed converter is analyzed and some important characteristics are obtained. The design and implementation of the complete power supply are also shown. The UC3872 integrated circuit is proposed in order to operate the converter at resonance, allowing us to maintain a good response disregarding the changes in electric parameters of the transformer-ozonizer pair. Experimental results for a 50-W prototype are also provided.

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.

High Voltage Power Supply for Ozone Generation Based on Piezoelectric Transformer

Even though nowadays piezoelectric transformers (PT) are only available with low power rating, there exist several low power applications of ozone generation in which the use of this novel technology could be advantageous. Hence, the aim of this paper is to evaluate the possibilities of using PTs in the implementation of high voltage power supplies for ozone generation. First, the possible topologies that can be used to drive the PT are identified. Then, the half bridge inverter operating under zero voltage switching (ZVS) is investigated, and the effect of the silent discharge generator (SDG) on the converter operation is analyzed. A new control circuit that allows the ZVS operation is proposed. The control circuit operates in closed loop by measuring the phase between the PTs resonant current and the switching pattern and adjusting the switching frequency to the optimum value to assure ZVS. A laboratory prototype for a 6 W SDG was tested, and obtained experimental results are shown.

Arc stabilization in low-frequency square-wave electronic ballast for metal halide lamps

Discharge lamps present a negative dynamic characteristic that makes necessary using a current limiting element. In high frequency resonant ballasts current limitation is performed by the output resonant tank, but in low-frequency square-wave electronic ballasts arc stabilization is accomplished by stage feeding the square wave inverter. Therefore, the design of the input converter must be made taking into account the lamp dynamic characteristic. This paper presents a new procedure for obtaining the small-signal dynamic characteristic of metal halide lamps is proposed. Using the proposed methodology the small-signal characteristic of a 70 W is obtained, this characteristic is then used for the design of an electronic ballast based on a buck-boost converter followed by a full bridge inverter. The limits for stable operation obtained are verified using a laboratory prototype.

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

Nowadays, permanent emergency lighting systems (PELS) are widely used in many applications: emergency exit indication, lighting in critical or strategic points. Limitation in operation hours in classical lamps (10000-20000 hours 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 100000 hours) of high efficiency LEDs with a very simple electronics circuitry implies an interesting solution for this type of application. A 30 lumens and 1 hour PELS has been built and tested. A low cost power supply has been built and used as battery charger and LED driver.

Driver for high efficiency LED based on flyback stage with current mode control for emergency lighting system

Nowadays, permanent emergency lighting systems (PELS) are widely used in many applications: emergency exit indication, lighting in critical or strategic points. Limitation in operation hours in classical lamps (10.000-20.000 hours for fluorescent lamps) implies short lamp replacement times and, therefore, high maintenance costs. This paper shows a driver based on a flyback circuit for a PELS system. Control in current mode operation assure current constant in LEDs in any battery condition. The long operation life (above 100.000 hours) of high efficiency LEDs with a very simple electronics circuitry implies an interesting solution for this type of applications. A 30 lumens and 1 hour PELS has been built and tested.

Small-Signal Modeling of Discharge Lamps Through Step Response and Its Application to Low-Frequency Square-Waveform Electronic Ballasts

In this paper, a simple method to obtain the small-signal model of discharge lamps, and particularly metal halide (MH) lamps, is proposed. A dc voltage source with a series resistor is used to supply the lamp at the required power level. Then, the lamp response against an input voltage step transient is analyzed. From this analysis, the parameters of the equivalent lamp model can be calculated. The proposed method allows obtaining the lamp model in a straight manner from a single test. With this technique, a 35-W MH lamp is modeled at two different power levels. A validation circuit, which includes a resistive ballast and a capacitance, is analyzed to evaluate the possibilities of the proposed modeling technique. The obtained experimental results are in good agreement with the theoretical analysis. The derivation of a time domain lamp model for SPICE-based computer simulators is also introduced. Finally, an example of application in low-frequency square-waveform electronic ballasts is presented