J. Cardesin

University of Oviedo, Oviedo, Asturias, Spain

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Publications (74)74.98 Total impact

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    ABSTRACT: Parallel connection of several LED strings is a practical way to reduce the overall lamp voltage when a large number of emitters is needed. However, this connection might lead to high current mismatches between strings due to the dispersion of characteristics that even binned devices feature. Several techniques have been proposed in order to eliminate or, at least, reduce the forward current mismatch between paralleled strings. Provided that a cost-effective design is pursued, passive self-equalization of LED strings will be studied in this paper, where the dynamic resistance will be considered as the equalizing resistor. Thus, a statistical study will firstly be developed on four commercial devices in order to determine the forward voltage deviation in both binned and unbinned LEDs. Then, the dynamic resistance will accurately be determined for the operating current in a wide temperature range by the procedure followed in previous works, since this parasitic effect will be employed as the equalizing resistor. The I-V and RD-Tj curves will be thus experimentally obtained for a large sample. Once the thermal and statistical characterizations are done, the study of the LED linear model will be performed in order to determine the impact on forward current mismatches that forward voltage and dynamic resistance variations imply in both binned and unbinned LEDs. Finally, experimental results will show that binned LEDs are suitable for self-equalization even for a tight current-mismatch tolerance, especially for a significant number of series-connected LEDs in each string.
    New Concepts in Smart Cities: Fostering Public and Private Alliances (SmartMILE), 2013 International Conference on; 01/2013
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    ABSTRACT: A low-cost 18W intelligent LED driver for energy savings is presented. The intelligent LED driver has a DALI interface that allows it to be included in an upper lighting smart grid. So, it must provide galvanic isolation. The proposed LED driver is based on a two stage scheme with 24V safety voltage. The first stage is based on a PFC Flyback converter operating in the boundary conduction mode, meeting the International Standard IEC61000–3–2 Class C. The second stage is based on 3×6W low-cost and efficient DC/DC buck converters for driving LEDs. The LED lamp has a built-in ambient light sensor that measures the lumen level of the ambient light and a low-cost microcontroller adjusts the emitted luminous flux in order to obtain the desired luminous level of the ambient light contributing to great energy savings. Experimental results validate the circuit proposed.
    New Concepts in Smart Cities: Fostering Public and Private Alliances (SmartMILE), 2013 International Conference on; 01/2013
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    ABSTRACT: One of the main concerns when designing dimming ballasts is the stability range that can be obtained in practical designs. Some applications require the output power to be reduced below 20% of its nominal value. The small-signal model of fluorescent lamps has proven to be a useful tool to describe the dynamic behavior of fluorescent lamps. These models can be used to analyze the lamp-ballast interaction and determine the stable control range. However, most of the small signal models that can be found in prior literature do not take into account the effect of the ambient temperature. In present work, the effect of the ambient temperature in the small signal characteristics of a compact fluorescent lamp is described. A temperature and power dependent double-pole double-zero model is proposed. This model is used to analyze the effect of the temperature in the stability range in a half-bridge resonant ballast.
    IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society; 01/2012
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    ABSTRACT: 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 closed 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.
    IEEE Transactions on Industry Applications 09/2009; · 1.67 Impact Factor
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    ABSTRACT: The use of high-efficiency LEDs in low-power lighting applications is growing continuously due to new advances in LED features. The lifetime of a low-power fluorescent lamp is around 5000 h. This implies short lamp-replacement times and high maintenance costs. The use of high-efficiency LEDs reduces drastically the maintenance costs due to the long lifetime (>50 000 h). One of the applications where using LED is very interesting is permanent emergency light systems. Generally, these circuits are based on a two-stage design, using two magnetic cores. This paper presents offline power LED driver and battery charger integrated in one magnetic core topology. Besides, the converter allows driving the LEDs in case of a line failure and it complies with the IEC 61000-3-2 Class C Standard.
    IEEE Transactions on Power Electronics 06/2009; · 4.08 Impact Factor
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    ABSTRACT: 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.
    IEEE Transactions on Power Electronics 05/2009; · 4.08 Impact Factor
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    ABSTRACT: The first LED diode was created in 1969. Since then, they have been experiencing a continuous improvement in luminous efficiency and power dissipation, achieving current AIInGaP and InGaN devices for yellow to red, and blue to green, including white, colours respectively. The improvement experienced in both luminous efficiency and power dissipation makes them interesting for lighting application in automotive industry, where the advantages offered are numerous, from a lower time response in brake lights to an operating life much higher than that of the vehicle itself [1], [2]. In the other hand, the improvement experienced in luminous efficiency and power dissipation allows the construction of most of the signal devices using just a few emitters [1]. Due to the points stated above, a comparison among the most efficient red, amber/yellow and white Power LEDs currently available from the leading manufacturers is proposed, offering a comparison in terms of luminous efficiency in nominal test conditions, thermal resistance between the junction and the slug and also giving a comparison about the performance depending on junction temperature between the two most efficient LEDs for each colour.
    Industry Applications Society Annual Meeting, 2008. IAS '08. IEEE; 11/2008
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    ABSTRACT: The use of high efficiency leds in low power lighting applications is growing continuously due to new advances in led features. The lifetime of low power fluorescent lamp is around 5.000 hours. This implies short lamp-replacement times and high maintenance costs. The use of high efficiency leds reduces drastically the maintenance costs due to the long lifetime (above 100.000 hours). One of the applications where using led is very interesting are Permanent Emergency Light Systems (PELS). Generally, these circuits are based on two-stage design, using two magnetic cores. This paper presents off-line power led driver and battery charger integrated in a one magnetic core topology. Besides, the converter allows driving the leds in case of a line failure and it complies with the IEC 61000-3-2 Class C Standard.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008 · 4.08 Impact Factor
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    ABSTRACT: 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.
    IEEE Transactions on Industrial Electronics 02/2008; · 5.17 Impact Factor
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    ABSTRACT: Discharge lamps present a negative dynamic characteristic that makes necessary to use 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 the stage feeding the square wave inverter. Therefore, the design of the input converter must be made taking into account the lamp dynamic characteristic. In the present paper, a new procedure to obtain the small-signal dynamic characteristic of metal halide lamps is proposed. Using the proposed methodology, the small-signal characteristic of a 70-W lamp 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.
    IEEE Transactions on Power Electronics 10/2007; · 4.08 Impact Factor
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    ABSTRACT: In this paper, parallel connection of high efficiency LEDs for lighting applications is studied. Unlike series connection, parallel connection of LEDs allows the operation of these devices at different current levels. Among other features, this allows the operation of the remaining LEDs if one of them fails. The main drawback of parallel connection is, as is very well known, current equalization and stable operation, due to the V vs. I characteristic of the LED. An active equalization and current limitation with MOSFETs is studied and implemented, thus obtaining a high current-low voltage power load. To supply this load, a 16 W synchronous flyback is used, in order to supply 4 high efficiency LEDs. The overall prototype design and construction is discussed, and electrical and light measurements are presented.
    Industrial Electronics, 2007. ISIE 2007. IEEE International Symposium on; 07/2007
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    ABSTRACT: The use of power LED is growing continuously, due to new advances and new devices with performances which increase day after day. Nowadays, a topic of interest in this context is the search for electronic converters in order to take advantage of LED performances. LEDs ballast design involves a multidisciplinary knowledge: photometric, thermal, power electronics and control techniques. This work focuses in to save potential pitfalls during ballast design for these new components. This paper evaluates the use of tapped-converters as LED drivers in low voltage applications. These topologies are derived from tapped- inductor DC-to-DC converters, in which the load is a connection of power LED. This load implies several restrictions in both power topology design and control method strategies. The work includes an extensive discussion about this topic, clarifies areas of application for each specific topology and includes a complete design example.
    Industrial Electronics, 2007. ISIE 2007. IEEE International Symposium on; 07/2007
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    ABSTRACT: 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
    IEEE Transactions on Power Electronics 06/2007; · 4.08 Impact Factor
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    ABSTRACT: 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
    IEEE Transactions on Power Electronics 06/2007; · 4.08 Impact Factor
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    ABSTRACT: In this paper, a study about acoustic resonance (AR) in low-wattage metal halide lamps is presented. The lamps are supplied with a typical low frequency square waveform on which a high frequency sinusoidal ripple is superposed. The goal is to emulate the same waveforms generated by a low frequency electronic ballast. In this way, the ARs that appear in the lamp can be characterized against ripple amplitude and frequency. Different lamp's manufacturers and burning hours are used. The obtained results are intended to be employed in further reliable designs of low-frequency square-waveform electronic ballasts. An example of application of the accumulated AR signatures in this type of electronic ballasts is carried out, and a standard proposal is presented
    IEEE Transactions on Power Electronics 06/2007; · 4.08 Impact Factor
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    ABSTRACT: 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
    IEEE Transactions on Plasma Science 03/2007; · 0.87 Impact Factor
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    ABSTRACT: The most commonly used power topology to drive metal halide lamps is based in three cascaded stages. The first stage is used for power factor correction, the second stage is used to stabilize the discharge and the last stage is used to turn the DC output of the previous stage to a low frequency AC square waveform suitable to supply the lamp. The dynamic impedance of the lamp does not allow using the power factor correction stage to stabilize the discharge. This is due to the fact that voltage in the bulk capacitor can not be changed fast enough to stabilize the lamp current. In this paper, a boost-type post-regulator working at the zero-duty-cycle limit is proposed to stabilize the discharge. This way, a non-linear post-regulator with very high efficiency is obtained. A simplified procedure to design the regulator is also presented in this paper. A laboratory prototype has been built to verify the proposed procedure.
    01/2007;
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    ABSTRACT: The analysis, design and implementation of a microcontroller-based electronic ballast to supply metal halide lamps are presented. The proposed power scheme is based on the integration of the buck and flyback converters. The former providing power factor correction and the latter controlling lamp power by supplying the lamp with a low frequency square-waveform current, which is a convenient way to avoid acoustic resonances in high intensity discharge (HID) lamps. Both converters operate in discontinuous conduction mode, thus allowing the use of only one high-frequency switch and simplifying the control. The electronic ballast is digitally controlled by using a low cost microcontroller PIC16F684. The microcontroller performs all the necessary tasks during starting, heating and steady state, including closed loop control of lamp current and protections. Experimental results for a 35 W metal halide lamp are presented
    IEEE Industrial Electronics, IECON 2006 - 32nd Annual Conference on; 12/2006
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    ABSTRACT: The use of piezoelectric transformers in electronic ballasts has been widely discussed in recent literature. In most of the applications, the piezoelectric transformer substitutes all the resonant tank components of a half-bridge resonant inverter. However, designing the inverter to keep zero-voltage-switching in all the operating range is difficult due to the high input capacitance of piezoelectric transformers. The simplest topology that can be used to drive a piezoelectric transformer is the class-e inverter. In present paper, a simple procedure to achieve ZVS using the input inductor of the class-e inverter is described. The proposed procedure has been used to design a laboratory prototype based on a radial-mode piezoelectric transformer
    Industry Applications Conference, 2006. 41st IAS Annual Meeting. Conference Record of the 2006 IEEE; 11/2006
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    ABSTRACT: This paper presents the analysis, design and experimentation of a closed-loop metal halide lamp ballast, which supplies the lamp with a low-frequency square waveform. First of all, a discussion related to the lamp parameter that should be regulated (power or current) is presented, since this issue has not been well addressed in previous literature. Experiments demonstrated that lamp current can be chosen to be kept constant during lamp life, because, on one hand, it can attenuate the effect of lumen depreciation with lamp ageing, and, on the other hand, the lamp power does not reach over-rated values during lamp life. In order to analyze the open-loop characteristic and design a suitable controller for the closed-loop operation, a dynamic model of the lamp-ballast system is developed. Therefore, considering the dynamic of the lamp current sensor, a PI controller is proposed to minimize the steady state error and provide a phase margin of about 80deg (fully stable system). Experimental results using a flyback-based ballast supplied from a non-regulated DC voltage source (100-150V) are presented to validate the theoretical analysis. It is demonstrated that the lamp current is kept constant at rated value (0.42A) within the whole input voltage range. The time response of the complete closed-loop system is about 5 ms
    Industry Applications Conference, 2006. 41st IAS Annual Meeting. Conference Record of the 2006 IEEE; 11/2006