High-density high-current fast-transient low-voltage DC-DC converters

Keywords

DC to DC converters

Abstract

Powering requirements of new and future high-performance, high-speed and highintegration density load of DSPs and microprocessors are continuously and increasingly becoming more stringent. More devices are being packaged on a single chip with increased integration density, causing higher load current demands and forcing their operating voltages to drop to levels below one volt. Moreover, such load speeds ( operating frequency) are increasing at a fast pace, and they switch the current they draw with increasingly higher slew rates (faster) causing larger voltage deviation during their transients, which should be limited to a very small value especially at low voltages to guarantee safe and high performance operation. To avoid distribution line parasitics and losses, such loads are not being powered by a DC voltage and current from a centralized power supply as used to be done in the past. Instead, a Distributed Power System (DPS) with a DC-DC converter at its near-load end is placed close to the load. These specially designed DC-DC converters are usually called Voltage Regulator Modules (VRMs) or Point-Of-Load (POL) Converters, and they must satisfy their stringent load requirements of low-voltage, high-current and fasttransient At the same time, they should maintain high-efficiency and high power density (smaller size) as their loads integration densities becomes higher also. Converter optimizations include power stage and control loop optimization.

The scope of this work is the POL and VRM DC-DC converters requirements, design and optimization. Topologies and control techniques for DC-DC converters are presented after reviewing loads powering requirements and DC-DC converters steadystate and transients design challenges and theoretical analysis. Non-isolated multiphase voltage-mode hysteretic controlled DC-DC converter control scheme and topology with current sharing is presented and supported by theoretical analysis with output voltage ripple, switching frequency and stability condition equations along with experimental results. This method combines the advantages of the interleaving technique and hysteretic control while achieving current sharing, which results in advantages that include fast transient response and equal current sharing between converter phases. Then, after reviewing selected isolated topologies, a control method for isolated half-bridge DC-DC converter topology, namely, Duty-Cycle-Shifted (DCS) control, is presented. This method allows soft-switching operation for half-bridge for higher efficiency at higher switching frequency and allows for reduced switching and isolation transformer-leakage inductance-related losses without the penalty of asymmetric components stresses and isolation transformer DC bias. Theoretical discussion and experimental results are presented and compared to other half-bridge control methods.

Another general control method for half-bridge topology, called Alternated Duty Cycle (ADC) control, is also presented. This method can achieve soft switching for halfbridge switches alternatively, if not for the two switches, and can do so without the penalty of asymmetric components stresses and isolation transformer DC bias, while

improving efficiency and maintaining thermal balance of the half-bridge switches. Theoretical discussion and experimental results are presented. Also presented is the interleaving method for isolated topologies, where the secondary side switches operate at lower switching frequency than the primary side switches to improve efficiency and to improve transient response. Meanwhile, both primary and secondary sides of the isolation transformers are connected in parallel, allowing sharing of currents at both primary and secondary sides. This method resulted in a family of interleaved isolated topologies. Theoretical description and experimental results are also presented. A Coupled-Inductors Currenr-Doubler (CICD) topology is then presented to allow further output voltage step-down by coupled inductors and to reduce the secondary side current-doubler input current. This is followed by a presentation of a non-isolated Half-Bridge-Buck (HBB) topology, where CICD topology can be also used, resulting in advantages including larger output voltage step-down and better self current sharing, especially when compared to non-isolated, two-phase buck topology. Theoretical analysis

and experimental results are presented. The presentation of control methods and topology for isolated and non-isolated DC-DC converters is followed by initial candidate concepts and work for control and topology techniques as well as programmable digital control. Digital control is discussed as a candidate for future DC-DC converters, while digital system structure, advantages, disadvantages and initial experimental setup are presented also. Moreover, an initial concept for future work on digital control is discussed, namely, the Maximum Efficiency Point Tracking (MEPT) method, which can be used to optimize a switche' s dead time

control issue by usmg adaptive control to achieve better efficiency and converter performance. Finally, the work is summarized and concluded and future research directions are presented.

Notes

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Graduation Date

2003

Advisor

Batarseh, Issa

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering

Department

Electrical Engineering and Computer Science

Format

PDF

Pages

215 p.

Language

English

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

Identifier

DP0029116

Subjects

Dissertations, Academic -- Engineering; Engineering -- Dissertations, Academic

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