F. Nuno

Power Supply for a High-Voltage Application

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.

Dynamic and Steady-State Models for the PRC-LCC Resonant Topology With a Capacitor as Output Filter

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.

High-efficiency and wide-bandwidth performance obtainable from a two-input buck converter

A study of the two-input post-regulators is carried out in this paper. In these post-regulators, only a part of the total power undergoes a switching conversion process, whereas the remainder of the power comes up to the load directly, with no power conversion process. Due to this fact, very high efficiency is achieved. Moreover, the stress in the semiconductors and the filter size are both much lower than in standard post-regulators. Two-input post-regulators require two-output main converters. However, many converter topologies can be easily adapted to supply two-output voltages with no efficiency penalty. Two-input postregulators can be used in many power converters. Multiple-output DC-to-DC converters and AC-to-DC power factor correctors are two good examples.

Intelligent and universal fast charger for Ni-Cd and Ni-MH batteries in portable applications

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.

A complete transformer electric model, including frequency and geometry effects

An electric model for transformers, including both frequency and geometry effects, is presented. From Maxwells equations an electric circuit which represents the transformer behavior is obtained. Expressions for calculating the circuit parameters from the winding layer geometry are given. The models inclusion in simulation programs and its limitations are discussed. Experimental results showing the accuracy of the model are provided.<<ETX>>

Design and analysis of thick-film integrated inductors for power converters

This paper describes the design procedures followed to obtain a thick-film inductor for its application in DC/DC power microconverters. The main characteristics of the new technology used are commented upon and design equations are given. Results are compared to those obtained by means of finite-element analysis tools. Details of some thick-film inductors developed with this technique (within the framework of the IMPASS Esprit Project (number 23910), financed by the European Community) are also given. The inclusion of one of these inductors in a 5-to-3.3-V DC/DC converter contributes to obtaining a very high power density: 6.25 W/cm/sup 3/.

1D/2D transformer electric model for simulation in power converters

This paper describes two complete electric models that characterize transformer windings. The models have the geometric information of the magnetic component and give accurate results for high frequency simulations. Both models are derived from Maxwell equations and the expressions to calculate the electric parameters directly from the geometry are shown. The models are suitable to be included in any simulation programs having very short generation time. This fact avoids the use of complex finite element analysis (FEA) tools.<<ETX>>

Very efficient two-input DC-to-DC switching post-regulators

A study of the two-input post-regulators is carried out in this paper. In these post-regulators, only a part of the total power undergoes a switching conversion process, whereas the remainder of the power comes up to the load directly, with no power conversion process. Due to this fact, very high efficiency is achieved. Moreover, the stress in the semiconductors and the filter size are both much lower than in standard post-regulators. Two-input post-regulators require two-output main converters. However, many converter topologies can be easily adapted to supply two output voltages with no efficiency penalty. Two-input post-regulators can be used in many power converters. Multiple-output DC-to-DC converters and AC-to-DC power factor correctors are two good examples.

A new control strategy for an AC/DC converter based on a piezoelectric transformer

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.

A very simple DC/DC converter using piezoelectric transformer

Piezoelectric transformers (PTs) have lately been looked upon as an attractive solution to reduce size and weight in AC/DC converters. This paper presents a topology that includes such a device while minimizing the number of additional components required for an adequate performance. An 8-watt AC/DC adapter (110 V/sub AC/, 12 V/sub DC/) operating at frequencies around 500 kHz is obtained using this topology.