A. Soto

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.

Power supply for a radio transmitter with modulated supply voltage

RF power amplifiers can save energy if the supply voltage is modulated dynamically. The power supply requires a low output capacitance to obtain a fast voltage modulation at very high efficiency and small size. These requirements become a challenge if a very good regulation under aggressive load current variations is also required. In this paper, a detailed analysis of the filter design and control of the buck converter leads to a very high efficiency, small size design that meets dynamic regulation requirements, even aggressive load current variations, with low output capacitance. Interleaving of buck converters proves to be the enabling solution. A prototype has been built and the measurements agree 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.

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

Optimum control design of PWM-buck topologies to minimize output impedance

The time domain control theory and the root-locus analysis are applied to the design of the PWM buck controller. A method that focuses on the optimization of the close-loop output impedance when a step load occurs is proposed. It accounts for duty cycle saturation. The best transient response achievable by a power stage is obtained. Analytical results are in good agreement with actual measurements.

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.

Design concepts and guidelines for VRMs from a power stage perspective

The VRM design involves meeting many requirements that oppose each other. A fast dynamic response of the VRM is of major importance to reduce the size and cost of the output capacitance. Meanwhile, the efficiency of the converter should be very high to meet specifications. This paper analyzes how this solution can be found, assuming no limitations in the control performance. The key design parameters will be highlighted (low inductance, output capacitance technology, multiphase converters) and design guidelines will be provided. A procedure to determine approximately the maximum number of phases that can make sense for a particular specification is derived.

Digital control for power supply of a transmitter with variable reference

RF power amplifiers can save much energy if they are supplied with a variable voltage as described in the state of the art. The design of the power supply of these amplifiers is challenging since many requirements have to be accomplished: very low output voltage ripple; wide output voltage variation at kHz frequencies; fast load current steps; etc. A typical solution is the use of a multiphase dc-dc converter based on the buck topology. In this paper, we propose the use of digital control for these power supplies. The main advantage is that current loops are removed. The design of this control circuit and main trade-offs are discussed. The results obtained from a 240 W prototype show the advantages and the limitations of this proposal.

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

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.