Showing papers by "J.A. Cobos published in 2001"

Power factor correction: a survey

Abstract: New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions to this problem to obtain sinusoidal line current and in addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

Miniaturised battery charger using piezoelectric transformers

Abstract: Piezoelectric materials are a technology that in recent years have raised enormous interest for their possible use as power transformers Their main features are high power densities, absence of electromagnetic noise and high voltage isolation capability This paper presents the results obtained in a prototype of a miniaturized battery charger for mobile phones Due to the reduced size of the piezoelectric transformers, the charger has been introduced in a plug type case, smaller than a matchbox

A new driving scheme for synchronous rectifiers: single winding self-driven synchronous rectification

Abstract: Single winding self-driven synchronous rectification (SWSDSR) approach is a new driving circuit that overcomes the limitations of the traditional driving schemes, becoming an interesting alternative to supply new electronic loads such as microprocessors. Traditional self-driven synchronous rectification (SDSR) technique has shown very good performance to improve efficiency and thermal management in low-voltage low-power DC/DC converters, however it can not be extended to the new fast dynamic, very low voltage applications. SWSDSR scheme is based on an additional winding in the power transformer (auxiliary winding). It allows for maintaining the synchronous rectifiers (SRs,) on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. It also makes it possible to drive properly the SRs even in very low voltage applications, 1.5 V or less. Coupling of the windings strongly affects the performance of the SWSDSR technique. The influence of the coupling between the different windings is analyzed through simulations of different transformers designed for the same application. Models of transformers are generated with a finite element analysis (FEA) tool. Goodness of the SWSDSR scheme is validated through experimental results.

Buck+half bridge (d=50%) topology applied to very low voltage power converters

Abstract: Buck+Half Bridge (d=50%) topology is a very suitable circuit for low output voltage, high output current applications with a wide input voltage range. Its small signal transfer function is very complex and should be considered to optimize the dynamic response, efficiency and size of the power converter. Small signal and large signal behavior of this topology are analyzed through their corresponding average models. Design guidelines, drawn from this analysis, are applied on two low-voltage (1.5 V) wide input voltage prototypes to validate the goodness of this topology.

Using parallel windings in planar magnetic components

Abstract: The use of parallel windings is a very common practice in planar magnetics, where the copper thickness is usually very low to handle typical current values. Besides, the use of parallel turns allows applying better interleaving among the different windings. This work presents a review of the proper modeling strategy in order to take into account the current distribution through each paralleled winding. Different winding strategies have been analyzed using a finite element analysis (FEA) based model in order to obtain the proper procedure to place parallel windings in planar magnetics. Although the modeling strategy presented is valid for any winding strategy (planar and concentric), it has been applied in order to test planar components.

Design considerations of multi-layer piezoelectric transformers

Abstract: Piezoelectric transformers (PTs) present an attractive solution compared with magnetic transformers because they have alternative characteristics that are appropriate for particular applications, namely high power density and high isolation levels with low EMI content. The behavior of PTs is very dependent on the material type, geometry and number of layers. Since PTs should be used in a power topology, it is necessary to establish design rules in order to select the proper specifications of the PT for each particular application. This work presents some design guidelines as well as the description of the influence of several constructive parameters on the behavior of the multi-layer PTs.

1D modeling of multi-layer piezoelectric transformers

Abstract: This paper presents a general procedure to obtain 1D models of multi-layer piezoelectric transformers. A detailed description of how to model the different parts of the transformer-active layer, bulk material, connection and mechanical restrictions-is given. Temperature effects on piezoceramic properties are taken into account. Simulated and measured results are also presented.

Converter for telecom and datacom compatibility

Abstract: The 48 V DC distribution is considered as a standard in the telecom world while datacom equipment is usually fed from AC mains. This fact has led Alcatel to propose a new power architecture for datacom-telecom applications where the system performance is improved, taking into account the existence of both types of loads. The new system is based on a high voltage rectified AC distribution. This new system should be compatible with the traditional telecom 48 V plants to take advantage of the existing installations. In this paper, a high efficiency converter designed to work with both distributions (rectified AC and 48 V) is proposed. This converter allows a smooth transition to implant the new system providing compatibility between both. The selection process, design and experimental results are included in the paper.

1D analytical procedure to calculate magnetic components parameters

Abstract: This work presents a procedure valid to solve small signal tests of magnetic components (inductors and multiwinding transformers) by means of analytical expressions. The method is based on the use of the transmission line 1D model of the magnetic component. Since the test can be analytically solved, the procedure allows skipping the use of electrical simulators in order to solve the small signal analysis. The procedure is valid for general cases, and therefore it can be implemented using mathematical packages (Mathcad, Madab, Mathematica, etc.) or using programming languages. The method has been validated by means of comparisons with actual measurements as well as FEA solvers results.