P. Alou

Nonlinear digital control breaks bandwidth limitations

The bandwidth achievable by using linear control in SMPS is limited either by the switching frequency or by the robustness of the system. Fast transient response requires high switching frequency. However, lower switching frequencies could be more suitable to maximize efficiency. On the other hand, if high switching frequency is not a problem, high bandwidth is difficult to obtain because of noise, plant variation and non-idealities of the error amplifier. This paper proposes two different approaches based on the combination of nonlinear control with linear control to break these limitations. These strategies are applied for dynamic voltage scaling and two prototypes are built to validate the concepts.

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

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 Pontryagins 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.

Analysis of the Buck Converter for Scaling the Supply Voltage of Digital Circuits

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 Pontryagins 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.

Current Self-Balance Mechanism in Multiphase Buck Converter

Some of the recent applications in the field of the power supplies use multiphase converters to achieve fast dynamic response, smaller input/output filters, or better packaging. Typically, these converters have several paralleled power stages, with a current loop in each phase and a single voltage loop. The presence of the current loops avoids current imbalance among phases. The purpose of this paper is to demonstrate that, in CCM, with a proper design, there is an intrinsic mechanism of self-balance that reduces the current imbalance. Thus, in the buck converter, if natural zero-voltage switching (ZVS) is achieved in both transitions, the instantaneous inductor current compensates partially the different DC currents through the phases. The need for using n current loops will be finally determined by the application but not by the converter itself. Using the buck converter as a base, a multiphase converter has been developed. Several tests have been carried out in the laboratory and the results show clearly that, when the conditions are met, the phase currents are very well balanced even during transient conditions.

Minimum Time Control for Multiphase Buck Converter: Analysis and Application

The combination of minimum time control and multiphase converter is a favorable option for dc-dc converters in applications where output voltage variation is required, such as RF amplifiers and dynamic voltage scaling in microprocessors, due to their advantage of fast dynamic response. In this paper, an improved minimum time control approach for multiphase buck converter that is based on charge balance technique, aiming at fast output voltage transition is presented. Compared with the traditional method, the proposed control takes into account the phase delay and current ripple in each phase. Therefore, by investigating the behavior of multiphase converter during voltage transition, it resolves the problem of current unbalance after the transient, which can lead to long settling time of the output voltage. The restriction of this control is that the output voltage that the converter can provide is related to the number of the phases, because only the duty cycles at which the multiphase converter has total ripple cancellation are used in this approach. The model of the proposed control is introduced, and the design constraints of the buck converters filter for this control are discussed. In order to prove the concept, a four-phase buck converter is implemented and the experimental results that validate the proposed control method are presented. The application of this control to RF envelope tracking is also presented in this paper.

Design methodology for dynamic voltage scaling in the buck converter

Dynamic voltage scaling is a technique that reduces the energy consumption in electronics systems. This paper deals with the design of the buck converter to meet dynamic voltage specifications and regulation under load current steps. A design methodology is proposed. Filter designs, number of interleaved phases, optimum switching frequency and control speed are key parameters that are taken into account in this methodology. The minimum time control law enables the maximum inductance design at the optimum switching frequency, thus, maximizing the efficiency of the converter. This methodology is applied to a particular specification for dynamic voltage scaling and a prototype is built to validate the concepts

A simple single-switch single-stage AC/DC converter with fast output voltage regulation

In this paper, a simple single-stage AC/DC converter based on the flyback topology is presented. With a single switch, a fast-regulated output voltage is achieved and, although the line current is not sinusoidal, the converter complies with the Standard IEC 1000-3-2 about low frequency harmonies for a medium power range (50-500 W). The major advantages of this converter are the size and the efficiency. Design guidelines, analysis of the line current, and extensions to other topologies are analyzed. Experimental results are included in the paper.

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

Comparison of current doubler rectifier and center tapped rectifier for low voltage applications

It is well known that the current doubler rectifier is very suitable for low voltage (1V-2V) and very high current (50A-100A) dc-dc converters. However, at lower current applications (30A, 20A, 10A), it is not clear which is the more appropriate rectifier the current doubler or the center tapped. The goal of this paper is to identify the application area of these rectifiers. The output current together the output current ripple/output current ratio (/spl Delta/I/I/sub O/) are important parameters to select the more suitable rectifier.

The future DC-DC converter as an enabler of low energy consumption systems with dynamic voltage scaling

The energy consumption in notebooks and multimedia terminals limits autonomy, high performance and further reduction of size. The DVS represents an alternative solution to current techniques that dramatically reduces energy consumption in digital systems. The power supply becomes a very important part of the system as it enables the voltage scaling. This paper analyzes the requirements and challenges for these power supplies, highlighting the interesting solutions and the research trends.