Showing papers by "J.A. Cobos published in 2003"

Single phase power factor correction: a survey

Abstract: New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal. 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 and low power 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.

A simple dc-dc converter for the power supply of a cochlear implant

Abstract: A resonant topology based on class-E is presented as the power supply of a cochlear implant. This topology has the important advantage of a small number of components and a grounded single switch. Zero voltage switching can be achieved, which significantly reduces switching losses and improves efficiency. A circuit has been designed, built and tested in order to check the feasibility of the topology for the mentioned contactless application. The results are very good, the efficiency has been clearly improved compared to the former system and the autonomy has increased.

Magnetic integration for interleaved converters

Abstract: In this paper several techniques for integration of magnetic components in interleaved converters are analyzed Magnetic components define the way the energy is transformed Several opposite approaches can be considered: from decoupled integrated inductors to tightly coupled inductors The integration of inductors in the same core for multiphase converters is especially analyzed from the point of view of size, losses and coupling

Analysis of the buck converter for scaling the supply voltage of digital circuits

Abstract: The energy consumption in mobile systems has become a big challenge that limits high performance and autonomy in mobile systems. The dynamic voltage scaling (DVS) is a recent technique that reduces energy consumption varying dynamically the supply voltage of the system accordingly to the clock frequency. The buck topology is a good candidate to supply step variations of the output voltage meeting the DVS requirements. In this paper, it is analyzed which is the fastest output voltage evolution that can provide the Buck topology. The minimum time state transition in the buck converter and its corresponding control law are obtained applying the maximum principle or Pontryagin's principle. Design criteria for the buck topology are derived from this result. The analysis is extended to a multiphase buck converter. The minimum time control law is validated in a prototype. The measurements are in good agreement with the theoretical results.

Mixed analytical and numerical design method for piezoelectric transformers

Abstract: Analytical models are widely used for piezoelectric transformers (PTs) design. In this paper, the additional usefulness of finite element analysis (FEA) for PT design will be shown. With FEA it is possible to optimize the PT design not only by maximizing the energy transference, but cleaning the working frequency range of spurious modes (geometrical 2D/3D effects). Besides, FEA tools allow studying other interesting aspects of the PT design such as the manufacturing tolerances or the influence of the fixing layer on the PT performance (which is a critical design point). A mixed analytical and numerical design method for PT is proposed.

A two stage voltage regulator module with fast transient response capability

Abstract: Multiphase converters based on buck topology are very good candidates for voltage regulator modules that convert from 5 V or 12 V down to 1.5 V. However, their applicability is very restricted at higher input voltages (24 V, 48 V). In those applications where a fast dynamic on-board DC/DC converter with a high input voltage (24 V, 48 V) is required, interleaved buck topology can still be useful if a "DC/DC current transformer" is used to adapt the voltage and current levels, providing a symmetric operation (around 50% duty cycle) to the multiphase converter. A "two phases synchronous buck + current fed push pull (50%)" prototype is tested to validate the concept in a 24 V to 1 V-50 A converter with a fast transient response capability (20 A/gs). Measured efficiency is 84% at 1 V, 50 A (91% at 25 A). The proposed solution is compared with other candidates for the same specifications: "single stage half bridge" converter, "two-phases half bridge" converter and "three-phases half bridge" converter.

Harmonic reducer converter

Abstract: A new strategy to accomplish low-frequency Regulation EN 61000-3-2 at system level is proposed in this paper. By means of a simple converter, connected in parallel with the loads, the harmonic currents generated by them are greatly reduced, it being unnecessary to include additional power-factor-correction converters. This approach is based on the well-known parallel active power filters, but the difference is that it is placed on the DC side. Its position, at the rectified line voltage, produces some important advantages such as a simple power stage, a simple analog control, and flexibility in the design of the system. Moreover, this converter features high efficiency and small size. The experimental results show the benefits of this solution.

Magnetic-less converter based on piezoelectric transformers for step-down DC/DC and low power application

Abstract: This paper presents a very simple step-down DC/DC low power converter based on piezoelectric transformers (PTs) without any magnetic component. PTs become very interesting in this kind of applications comparing with magnetic transformers due to the higher power density. It is important to highlight that the PT has been specifically designed to avoid the use of magnetic components. Dynamic response of the power stage with the PT is analyzed, achieving a 2.5 kHz bandwidth. The use of a PT allows a wide input voltage range (20 V-75 V), 3 V, 1 W DC/DC converter.

Analytical thermal model for magnetic components

Abstract: 1D thermal models are often used in the design of magnetic components in order to obtain an optimum design for a specific application. These thermal resistor-based models usually consider a thermal network based on the analogy between electricity and heat transfer equations. These models consider heat transfer in axial or radial direction using different electric elements, and using this analogy, model heat transfer through each object. Usually, convection and radiation effects are not taken into account when there is an enclosure. If temperatures become higher, these effects may become important. This work presents a procedure to model heat transfer in a magnetic components considering convection and radiation heat transfer in the window air area. Comparisons with finite element analysis are carried out in order to show the accuracy of the proposed method. The model that is presented is nonlinear. Therefore, a numerical method is shown in order to obtain the solution of the model using an iterative algorithm.

Low output voltage AC/DC converter with a new scheme of synchronous rectification that complies with IEC 1000-3-2 regulations

Abstract: The aim of this paper is to study the performance of an AC/DC converter with low output voltage and low input current harmonic content. In order to obtain low output voltages with a high efficiency, synchronous rectification is mandatory. When the output voltage is low, it is very difficult to use self-driven synchronous rectification and additional windings are used to properly drive the metal oxide semiconductor field effect transmitters (MOSFETs). Besides this, IEC 1000-3-2 regulations impose low input current harmonic contents for power levels higher than 75 W. In this paper, a recently proposed synchronous rectification scheme is combined with a modified input current shaper to design a 100 W, 3.3 V AC/DC converter that complies with IEC 1000-3-2 regulations. The efficiency obtained in the prototype was very high for this application (86%) and both the size increase and the cost increase were quite low in comparison with the original topology with no synchronous rectification and no IEC 1000-3-2 compliance.

Multi-output half-bridge converter with single-winding self-driven synchronous rectification

Abstract: This paper presents a multi-output half-bridge converter with single winding self-driven synchronous rectification (SWSDSR), which is a very suitable topology for high-current low-voltage applications with a wide input voltage range. Important benefits as high efficiency and multi-output capability are obtained. With the proposed converter it is possible to drive all synchronous rectifiers through the gate voltage waveforms obtained from only one additional winding. Design considerations and experimental results of a 25W laboratory prototype are included in the paper.

Multiphase voltage regulator module with self-driven synchronous rectification

Abstract: This paper propose a multiphase voltage regulator module (VRM) based on the symmetrical half-bridge topology employing the single winding self-driven synchronous rectification (SWSDSR) scheme. Main advantages of the proposed VRM are the fast transient response and the simplicity in the driving of the synchronous rectifiers. Proposed VRM was evaluated on a 48 V/1.5 V, 60 A 4-phases VRM. Design considerations as well as experimental results are included in the paper.

Design Guidelines for DC-DC Converters with Dynamic Voltage Scaling

Abstract: Abstract The energy consumption in wireless systems limits autonomy, high performance and further reduction of size. Dynamic Voltage Scaling(DVS) is an alternative solution that can dramatically reduce energy consumption in digital systems. The power supply becomes a very important part of the system in this technique as it enables the voltage scaling. This paper deeply analyses the requirements and challenges for these power supplies, clarifying the design issues and highlighting available interesting solutions and research trends.