A novel control scheme for improving the power efficiency of low-voltage dc-dc converters for battery-powered, portable applications is presented. In such applications, light-load efficiency is crucial for extending battery life, since mobile devices operate in stand-by mode for most of the time. The proposed technique adaptively reduces the inductor current ripple with decreasing load current while soft switching the converter to also reduce switching losses, thereby significantly improving light-load efficiency and therefore extending the operation life of battery-powered devices. A load-dependent, mode-hopping strategy is employed to maintain high efficiency over a wide load range. Hysteretic (sliding-mode) control with user programmable hysteresis is implemented to adaptively regulate the current ripple and therefore optimize conduction and switching losses. Experimental results show that for a 1-A, 5- to 1.8-V buck regulator, the proposed technique achieved 5% power efficiency improvement (from 72% to 77%) at 100 mA of load current and a 1.5% improvement (from 84% to 85.5%) at 300 mA, which constitute light-load efficiency improvements, when compared to the best reported, state-of-the-art techniques. As a result, the battery life in a typical digital signal processing microprocessor application is improved by 7%, which demonstrates the effectiveness of the proposed solution.

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A high efficiency, soft switching DC-DC converter with adaptive current-ripple control for portable applications

The low-voltage synchronous rectifier buck topology suffers from low efficiency at light loads due to dissipation that does not scale with load current In this paper we present a method for improving light-load efficiency in synchronous buck converters by reducing gate drive losses We propose a new gate drive technique whereby the gate voltage swing dynamically scales with load current such that gate drive loss is traded for conduction loss Since conduction losses scale with the square of load current, an optimal gate swing exists that, at light loads, is shown to be less than the supply voltage Using this method we obtain a 625% increase in converter efficiency at a load current of 10 mA and operating at a constant switching frequency of 2 MHz

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A constant-frequency method for improving light-load efficiency in synchronous buck converters

At present, power shortage became a huge problem in many countries, due to cumulative load demand which cannot be met by Conventional Energy Power Generation. These challenging situations lead researchers to focus on non-conventional energy sources to extract Electric Power. In order to extract the electric power, DC–DC converters are adopted at the primary stage to increase the efficiency Power Conversion. This paper presents an assessment of current and future trend of non-isolated DC–DC converters (Such as Buck–boost, Cuk and Sepic) with various parameters and are analyzed using MATLAB Simulink. Based on the simulation result, the performances of non-isolated converters are evaluated and are helps to determine the suitable converter with a particular power rating for renewable energy based applications. In addition, the state space mathematical modeling of DC–DC converters are also presented which will be useful in the design of controllers for different non isolated DC–DC converters.

An assessment on performance of DC–DC converters for renewable energy applications

Sensing current is a fundamental function in power supply circuits, especially as it generally applies to protection and feedback control. Emerging state-of-the-art switching supplies, in fact, are now exploring ways to use this sensed-current information to improve transient response, power efficiency, and compensation performance by appropriately self-adjusting, on the fly, frequency, inductor ripple current, switching configuration (e.g., synchronous to/from asynchronous), and other operating parameters. The discontinuous, non-integrated, and inaccurate nature of existing lossless current-sensing schemes, however, impedes their widespread adoption, and lossy solutions are not acceptable. Lossless, filter-based techniques are continuous, but inaccurate when integrated on-chip because of the inherent mismatches between the filter and the power inductor. The proposed GM-C filter-based, fully integrated current-sensing CMOS scheme circumvents this accuracy limitation by introducing a self-learning sequence to start-up and power-on-reset. During these seldom-occurring events, the gain and bandwidth of the internal filter are matched to the response of the power inductor and its equivalent series resistance (ESR), effectively measuring their values. A 0.5 mum CMOS realization of the proposed scheme was fabricated and applied to a current-mode buck switching supply, achieving overall DC and AC current-gain errors of 8% and 9%, respectively, at 0.8 A DC load and 0.2 A ripple currents for 3.5 muH-14 muH inductors with ESRs ranging from 48 mOmega to 384 mOmega (other lossless, state-of-the-art solutions achieve 20%-40% error, and only when the nominal specifications of the power MOSFET and/or inductor are known). Since the self-learning sequence is non-recurring, the power losses associated with the foregoing solution are minimal, translating to a 2.6% power efficiency savings when compared to the more traditional but accurate series-sense resistor (e.g., 50 mOmega) technique.

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An Accurate, Continuous, and Lossless Self-Learning CMOS Current-Sensing Scheme for Inductor-Based DC-DC Converters

This paper presents an inductive DC-DC boost converter for energy harvesting using a thermoelectric generator with a minimum startup voltage of 70 mV and a regulated output voltage of 1.25 V. With a typical generator resistance of $40~\Omega $ , an output power of $17~ {\mu }\text{W}$ can be provided, which translates to an end-to-end efficiency of 58%. The converter employs Schmitt-trigger logic startup control circuitry and an ultra-low voltage charge pump using modified Schmitt-trigger driving circuits optimized for driving capacitive loads. Together with a novel ultra-low leakage power switch and the required control scheme, to the best of the authors’ knowledge, this enables the lowest minimum voltage with fully integrated startup.

Fully Integrated Startup at 70 mV of Boost Converters for Thermoelectric Energy Harvesting

A comprehensive power analysis, keeping integrated circuits in mind, is presented while highlighting all conduction, switching, and dynamic power losses in a DC-DC converter. Synchronous rectification, zero-voltage switching, mode-hopping, and variable frequency operation are evaluated. The efficiency for constant frequency CCM, constant frequency DCM, and constant on-time, variable frequency DCM techniques is analyzed and the optimum technique is derived. It is concluded that a mode-hopping converter employing an asynchronous, constant on-time, variable frequency DCM operation for low output currents and a synchronous, constant frequency CCM operation for high load currents yields the best efficiency performance.

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A comprehensive power analysis and a highly efficient, mode-hopping DC-DC converter

This paper investigates the adverse effects of familiarity and human factors issues associated with the reliability of low-cost warning devices at level crossings. The driving simulator study featured a repetitive, low workload, monotonous driving task in which there were no failures of the level crossing (control) or prolonged or intermittent right-side failures (where the device reverts to a safe failure mode). The results of the experiment provided mixed support for the familiarity hypothesis. Four of the 23 participants collided with the train when it first appeared on trial 10 but safety margins increased from the first train to the next presentation of a train (trial 12). Contrary to expectations, the safety margins decreased with repeated right-side failure only for the intermittent condition. The limited head movement data showed that participants in the prolonged failure condition were more likely to turn their head to check for trains in the right-side failure trials than in earlier trials where there was no signal and no train. Few control participants turned their head to check for trains when no signal was presented. This research highlights the need to consider repetitive tasks and workload in experimental design and accident investigation at railway level crossings.

M. Gildersleeve

Papers

A comprehensive power analysis and a highly efficient, mode-hopping DC-DC converter

Effects of Driver Familiarity and Prolonged or Intermittent Right-Side Failure on Level Crossing Safety