M. Rascon

New driving scheme for self driven synchronous rectifiers

Self-driven synchronous rectification (SDSR) is a very good technique to improve efficiency and thermal management in low output voltage converters. In this paper, a new scheme to drive the synchronous rectifiers (SRs) is proposed. It allows for maintaining the SRs on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. It also makes possible to drive properly the SRs even for applications where output voltage is lower than 3.3 V, namely 1.5 V. Furthermore, driving losses are very low, since the discharge of one MOSFET is used to charge the other and vice versa. This scheme has been validated in two prototypes.

Design of a low output voltage DC/DC converter for telecom application with a new scheme for self-driven synchronous rectification

In this paper, the design and experimental results of a very low output voltage DC/DC converter for a specific telecom application (1.5 V, 10 A) is presented and analyzed. Several topologies have been compared and analyzed, not only from the point of view of size (15 W/inch/sup 3/, 10 mm of height) and efficiency (>85%), but also regarding the dynamic response of the converter to supply pulsating loads (80 A//spl mu/s). A new driving scheme for self-driven synchronous rectification (SDSR) is used. It allows use of the standard half bridge topology, which is very suitable for such a wide input voltage range (36 V-72 V).

A low power topology derived from flyback with active clamp based on a very simple transformer

This paper presents and analyzes a low power (10W) topology derived from flyback with active clamp based on very simple and low cost transformers. The main feature of this flyback topology is that the ratio between magnetizing inductance and the series inductance (leakage or integrated inductor) is very low (around 10/1). Operation of the topology is analyzed and several transformer configurations are considered. Performance of this topology are validated in three prototypes developed for an automotive application (VIN =42V, VOUT = 3.3V, IOUT = 5A). The proposed solution achieves a promising trade-off between efficiency and cost in low power applications with medium or high input/output voltage ratio

Several alternatives for low output voltage on board converters

This paper shows several approaches to generate low output voltage (3.3 V and 1.5 V) through on board converters. They all are supplied from a DC voltage ranging between 3 V and 6 V (valid for 5 V or 3.3 V input). With such low input and output voltages, synchronous rectification is mandatory to keep efficiency at reasonable levels. Magnetic components play a key role when Self Driven Synchronous Rectification (SDSR) is used. Several technologies have been used to build them, namely standard multilayer PCB, specific flex foils and thick film on ferrite. Three prototypes have been built using these technologies.

Design of very low profile magnetic components using flex foils

Several magnetic components (transformers and inductors) have been designed with very low profile (4 mm height) cores. To achieve such a low height, full custom cores have been used, together with an advanced technology (flex foils) for the windings. This freedom in the selection of dimensions and materials makes the design procedure completely different to the traditional schemes with commercial cores. The process used to obtain an optimum design is described in this paper. It is based on the use of models based on finite element analysis (FEA) tools, and spreadsheets. This procedure has been applied to the design of a transformer and an inductor, with a size of 10/spl times/10/spl times/4 mm/sup 3/ for each, to be used in an onboard power converter in telecommunication systems. Experimental results of a 5 W, low output voltage (3.3 V/spl times/1.5 A) prototype with these magnetic components are included in the paper.

A high efficiency voltage regulator module with single winding self-driven synchronous rectification

A high-current (60 A) low-voltage (1.5 V) DC/DC converter is designed and tested. Center-tapped and Current-doubler rectifiers are compared for high current fast dynamic applications. The selected topology is the half-bridge with current-doubler rectifier and single winding self-driven synchronous rectification (SWSDSR). This topology is very suitable for high-current low-voltage applications. However SWSDSR is successfully used only if all the parasitic inductances (transformer and layout) are minimized. Measured efficiency is 88% at full load 60 A.

Low profile and low output voltage DC/DC converters for on-board power distribution using planar magnetics

This paper describes two on-board power converters using new technologies to develop planar magnetics. Technologies involved are thick film on ferrite and very thin flex coils. New models of the high-frequency planar magnetics have been developed, useful both for the design of the custom made magnetics and for the simulation of the DC/DC power converters. Prototypes built provide 3.3V (5W) and 1.5V (1.5W) from a 5V input supply. The height of the power converters is 4mm (flex coils prototype) and 3mm (thick film prototype).

Systematic approach for developing large-signal averaged models of multi-output PWM converters

A systematic methodology for developing averaged models of multi-output PWM converters oriented to circuit simulators is presented. This methodology is intended to provide a reliable way of developing accurate multi-output averaged models. These models are able to predict the mode of operation of each output, even when the output filter inductors are coupled, and they also account for the nonideal characteristics of the switches.

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

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.

Comparing Si and SiC diodes performance in a commercial AC-to-DC rectifier with power factor correction

Improvements in power electronics are basically the result of research in two main fields: new topologies and new devices. A researchers efforts to bring about improvement because of topologies are always limited by the characteristics of the devices, so both facts must advance at one and the same time. This paper studies the impact of a new device on a classic structure of power factor correction: the boost converter.