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In this paper, the guidelines to design a high-voltage power converter based on the hybrid series parallel resonant topology, PRC-LCC, with a capacitor as output filter are established. As a consequence of the selection of this topology, transformer ratio, and therefore secondary volume, is reduced. The mathematical analysis provides an original equivalent circuit for the steady-state and dynamical behavior of the topology. A new way to construct high-voltage transformers is also proposed, pointing out the advantages and establishing an original method to evaluate the stray components of the transformer before construction. The way to make compatible the characteristics of both, topology and transformer is illustrated in the frame of a practical application. To demonstrate the feasibility of this solution, a high-voltage, high-power prototype is assembled and tested with good performance and similar behavior to the one predicted by the models. Experimental results are shown on this particular. Index Terms--DC-DC conversion, high voltage, resonant converters, X-rays.

Nowadays, piezoelectric transformers (PT) are a good alternative to substitute magnetic materials in ac/dc and dc-dc converters. They have high isolation voltage and operate at higher frequencies than magnetics, with lower losses. However, their optimum operating frequency exhibits a strong dependence on different parameters, such as temperature, load, or even voltage level applied. This is usually an inconvenience, because this drift affects PT gain and efficiency, which can vary enormously within a few hundred of hertz. On the other hand, not only is it necessary to ensure the PT is driven at the proper frequency--in terms of gain and efficiency, including zero voltage switching in the power stage--output voltage must also be regulated. In this paper, two simple feedback loops are implemented in a PT-based dc-dc converter. One of them adjusts the switching frequency to obtain the best gain and efficiency. The other one performs the output voltage regulation. Index Terms--Piezoelectric transformers (PTs).

In high-voltage dc power supplies (hundreds of kilovolts), avoiding the inductance in the output filter is an important asset. Thus, a capacitor as a unique component of that filter is preferable. On the other hand, a high-voltage step-up transformer shows a high capacitance in its secondary, which can be included in a resonant stage. Both capacitances, i.e., one from the filter and the other from the transformer, are separated by the output rectifier. When this rectifier is on, they are in parallel; when it is off, they are disconnected. A resonant stage where a very large capacitor appears and disappears several times in one period is not linear and has not been dynamically modeled before. This paper shows two simple models for the parallel-series (LCC-type parallel resonant converter) resonant topology with a capacitor as output filter. Its dynamics and steady state are studied and constitute an important help for any designer. Index Terms--DC/DC converters, high voltage, modeling, resonant converters.

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.

The usual way to avoid a computer shutdown during a mains failure is to connect an ac uninterruptible power system (UPS). However, there are other possibilities, such as using a dc UPS to obtain the dc output voltages directly from the battery instead of generating an ac voltage to feed the whole power supply. Thus, the topology must operate either from the ac mains or from a battery. A complete design of an ac/dc power supply with an internal dc UPS is presented in this paper. The solution is based on the coupling of the UPS to the main transformer. Moreover, the power supply meets all the requirements needed to be used as an Advanced Technology eXtended (ATX) PC power supply--multiple outputs, power and voltage ratings, size, protections, etc. A prototype has been fully developed and tested as a PC power supply. The autonomy achieved at full power is around 7 minutes. Index Terms--DC uninterruptible power system (UPS), multiple-output converter, PC power supply.

In this paper, a new fast charger is presented for Ni-Cd and Ni-MH batteries, which are the most frequently used in portable applications. In this charger, the control and supervision of the process has been entrusted to a microcontroller, which provides a powerful and intelligent tool to undertake complex tasks, and reduces the requested circuitry to the microcontroller itself and a few additional components. The resulting charger is able to work out the initial battery state (detecting deteriorated devices), decide the suitable way to charge it (ensuring a long cyclic life), and determine when the charge process must be finished. This way, the state of the battery is always controlled, preventing any damage to it and providing a fully protected operation mode. This paper summarizes the design and construction of the presented charger, as well as shows the experimental results obtained in the prototype tests. Index Terms--Battery charger, design, measurements, software.

Piezoelectric transformers (PTs) are an attractive solution to reduce size and weight in ac/dc converters. In this paper, a PT-based topology is presented together with a control method. As an application, an 8-W ac/dc adapter (110 [V.sub.AC] input, 12 [V.sub.DC] output) is presented operating at frequencies around 500 kHz. Index Terms--Battery charger, control strategy for piezoelectric transformer (PT) converters, piezoelectric transformers (PTs).

Due to their high power density and their low EMI generation, piezoelectric transformers (PTs) are an attractive solution to replace magnetic transformers in ac/dc converters. However, this substitution implies changes in the power topology and the control strategy because of the very frequency-dependent behavior of PTs, and their capacitive features. In previous works, some power topologies have been presented to deal with this new component, and frequency modulation has been assumed as the natural way to control the output voltage, sometimes in combination with pulse width modulation (PWM), to achieve both line and load regulation. In the frame of a particular application, this paper presents a new control method for PT-based converters. This control method is very simple to design, requires very few components and regulates the output voltage maintaining constant the frequency and the pulse width, trying to obtain the best characteristics from the piezoelectric device. Index Terms--DC-DC power conversion, piezoelectric devices.

The development of an automatic deceleration system for a winding machine in a siderurgy factory is presented in this paper. The proposed system controls the speed of a winding machine in order to obtain the optimum stop point in terms of security and fast production. The system is based on a microcontroller and an extremely simple hardware. The system has been tested for two years and results evince a very good mean time between failures. Index Terms--Automatic deceleration, control system, fast production, microcontroller, m.t.b.f. improvement.