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Even though, nowadays, piezoelectric transformers (PTs) 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 dosed loop by measuring the phase between the PT's 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. Index Terms--Control method, half-bridge inverter, high frequency, ozone generation, piezoelectric transformer (PT), Rosen-type PT, zero-voltage switching (ZVS).

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. Index Terms--Electronic lighting, high-brightness LEDs, light dimming.

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. Index Terms--Dimming, electronic ballast, fluorescent lamp, magnetic regulator, resonant tanks, variable inductance.

In this paper, a novel single-stage electronic ballast with a high power factor is presented. The ballast circuit is based on the integration of a buck converter to provide the power factor correction, and a flyback converter to control the lamp power and to supply the lamp with a low-frequency square-waveform current. Both converters work in discontinuous conduction mode, which simplifies the control. In spite of being an integrated topology, the circuit does not present additional stress of voltage or current in the main switch, which handles only the flyback or buck current, depending on the operation mode. To supply the lamp with a low-frequency square-wave current to avoid acoustic resonances, the flyback has two secondary windings that operate complementarily at a low frequency. The design procedure of the converters is also detailed. Experimental results from a 35-W metal halide lamp are presented, where the proposed ballast reached a power factor of 0.95, a total harmonic distortion of 30 % (complying with IEC 61000-3-2), and an efficiency of 90%. Index Terms--Acoustic resonance (AR), electronic ballast, high power factor (HPF), integrated buck flyback converter, metal halide lamp (MHL), single stage (SS).

This paper investigates the integrated buck-flyback converter (IBFC) as a good solution for implementing low-cost high-power-factor ac-dc converters with fast output regulation. It will be shown that, when both buck and flyback semistages are operated in discontinuous conduction mode, the voltage across the bulk capacitor, which is used to store energy at low frequency, is independent of the output power. This makes it possible to maintain the bulk capacitor voltage at a low value within the whole line voltage range. The off-line operating modes of the IBFC are also investigated to demonstrate that the control switch of the proposed converter handles lower root-mean-square currents than those in similar integrated converters. The off-line operation of the IBFC is analyzed to obtain the design characteristics of the bulk capacitor voltage. Finally, the design and experimental results of a universal input 48 V-output 100 W ac-dc converter operating at 100 kHz is presented. Experiments show that the IEC-61000-3-2 input current harmonic limits are well satisfied and efficiency can be as high as 82 %. Index Terms--Fast output regulation, integrated buck-flyback converter (IBFC), low cost, low current stress, power factor correction, single-stage (SS) ac-dc converter.

In this paper, a new control strategy that allows zero-voltage-switching (ZVS) operation of power converters using piezoelectric transformers (PTs) is proposed. The control circuit operates in a closed loop by measuring the phase between the PTs resonant current and the switching pattern and adjusting the switching frequency to the optimum value so that ZVS operation is assured. An innovative nonlinear regulator based on an analog multiplexer is presented. The regulator automatically swaps the signs of the sensed signal and the reference signal to allow generation of the adequate control action. A laboratory prototype for a 6 W resonant inverter was tested; obtained experimental results are also shown. Index Terms--Control circuit, half bridge converter, piezoelectric transformer (PT), power supply, zero-voltage-switching (ZVS).

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. Index Terms--Dimming, electronic ballast, fluorescent lamp, high frequency, magnetic regulator, soft start, variable inductor.

This paper proposes a metal halide lamp electronic ballast based on the integration of Zeta and Flyback converters, which are used to achieve power factor correction and lamp current stabilization, respectively. The proposed integrated converter allows to reduce the nmnber of ballast components without increasing the current stress in the shared switch. Thus, the lamp is supplied with a low-frequency square waveform that avoids the acoustic resonance phenomenon. The proposed topology has been implemented and validated by experimental results. Index Terms--Acoustic resonance (AR), ballast, high-intensity discharge (HID) lamps, integrated circnits, power electronics.

The use of high frequency (HF) square waveforms is a possible metal halide (MH) lamps supply method which can be implemented by means of non-resonant electronic inverters. This strategy can successfully avoid acoustic resonances appearance in such kind of lamps (theoretically, in a perfect square waveform, no power modulation is found). The main drawbacks of this kind of inverters are the electromagnetic interference emissions and the parasitic effects of the series igniters. This effect can spoil the square waveforms on the lamp, hence injecting HF harmonics in the lamp supply power spectrum, eventually leading to acoustic resonances appearance. In this paper, this effect is studied, in order to limit the values of the parasitic elements of the series igniter compatible with a proper operation of the HF inverter. Once these values are estimated, such an igniter has been built and tested, thus obtaining a practical HF (100 kHz) square waveform inverter with series igniter for 35-W MH lamps. Index Terms--Acoustic resonances, high frequency (HF) transformers, metal halide (MH) lamps, series igniters, square waveform inverters.

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. Index Terms--High intensity discharge (HID) lamp, low-frequency square-waveform (LFSW), metal halide discharge (MHD) lamp.

In this paper, a detailed study and experimentation on acoustic-resonances (AR) in low-wattage metal-halide lamps is presented. In order to excite the AR without extinguishing the electric arc, the lamps were supplied by means of a dc current with a superposed variable-frequency ac signal. By using this methodology, theoretical and experimental resonances were compared in terms of frequency, amplitude, and threshold-power level for their excitation. The experiments were carried out on four 35-W samples from each manufacturer (Osram and Philips), each of them with burning times of 100, 2500, and 5000 h, in order to cope with the full life of this type of lamps. AR maps for each lamp were obtained. These maps show not only the frequencies at which AR appear but also the amplitude of the resonances. The obtained AR maps are intended to be used by designers in order to know if a particular instantaneous lamp power waveform would be suitable to supply the lamp without generating AR. An application example on how to use these maps is also presented. Index Terms--Acoustic-resonance (AR) characterization, AR maps, electronic ballast, high frequency, metal-halide (MH) lamp, power harmonics.

In this article, an integrated parallel buck–boost and boost converter (IPB3C) is proposed as an electrolytic-capacitor-less light-emitting diode (LED) driver. The IPB3C provides a high power factor (PF) and low total harmonic distortion (THD). The driver is composed of two converters that are connected in parallel, using just one controlled switch. The buck–boost duty is to deliver constant power to the LED, while ensuring a good PF. The boost converter is employed to cancel the low-frequency ripple at the LED. In return, this decreases the flicker effect and only a relatively small capacitance is needed to fulfill the standard requirements. The buck–boost converter handles the full power of the LED, while the boost converter handles only a portion of the LED power. Thus, better efficiency is ensured by this parallel configuration compared to conventional cascaded integrated converters. Moreover, the voltage across the switch is low, as it is the higher, whether buck–boost or boost converter, but not the addition of both. In this article, the IPB3C is analyzed, and its design methodology is presented. A universal input voltage range prototype of the proposed converter supplying an LED lamp of 108-V/ 0.35-A is presented. The prototype shows high PF, nearly equal to one, very small THD, nearly zero, output voltage ripple of 4.5%, output current ripple of 19%, and high efficiency, equal to 92.4%. Moreover, the converter requires the use of a bulk capacitance of only 68 μF, while the required output capacitance is just 1 μF. [ABSTRACT FROM AUTHOR]

This letter presents a fluorescent-lamp improved arrangement in the half-bridge topology, putting one lamp in each branch of the converter. This arrangement allows a multilamp independent behavior. So, if one lamp is damaged, the other one keeps on working. In order to prove this independent arrangement, experimental results of one electronic ballast supplying two lamps with different wattage were shown. Index Terms--Fluorescent, lamp arrangement, multilamp.