Design of High Efficiency Step-Down Converter for Electro Chemical Energy Conversion

Recently the research interest in power electronics interface for fuel cell has increased. And the static characteristics of fuel cells show more than a 30% difference in the output voltage between no-load to full-load conditions. Thus inevitable decrease, which is caused by internal losses, reduces the utilization of fuel cells at low loads. Fuel cell is a electrochemical energy conversion device which directly produces electricity. Thus, a step-down converter is required to transfer  from a high input  voltage  to an efficient and constant low level voltage. Maintaining high efficiency under a wide loading range is important in fuel cell.The aim of this work is to design a stepdown converter with DCM operation under light load not only can  reach high  efficiency  in heavy-load, but also has great improvement in light-load efficiency. The output accuracy and the output ripples obtained are better than other converters under light-load and as good as a normal PWM converter under heavy-load. Circuit simplicity and high reliability are the major advantages of the proposed converter. Using this technique, the utilization factor and efficiency of the fuel cell is increased. And this paper, focuses on the simulation and implementation of DC-DC converter fed fuel cell. Validation of the proposed model is verified through simulation. Keywords: Fuel cell, Stepdown converter, PW

A Fast Response Dual Mode Buck Converter with Automatic Mode Transition

Dual mode DC-DC converters utilizing PWM and PFM modes of operation have been widely used to improve the efficiency over a wide range of the load current. Due to the highly varying nature of the load, it is beneficial to have the converter switch between the modes without an external mode select signal. This work proposes a new technique for automatic mode switching which maintains very high efficiency at light loads and at the same time, keeps the output well regulated during a load transient from sleep to the active state. The Constant On-time PFM scheme and a zero current detector avoids the use of an accurate current sensing block. The power supply rejection is also improved using feed-forward paths from the supply in both the PWM and PFM modes. A new implementation of the PWM controller with clamped error voltage required to meet the specifications is also shown. The proposed feedback implementation using a programmable current source and resistance provides smooth output programming

Stability analysis of switched dc-dc boost converters for integrated circuits

Boost converters are very important circuits for modern devices, especially battery- operated integrated circuits. This type of converter allows for small voltages, such as those provided by a battery, to be converted into larger voltage more suitable for driving integrated circuits. Two regions of operation are explored known as Continuous Conduction Mode and Discontinuous Conduction Mode. Each region is analyzed in terms of DC and small-signal performance. Control issues with each are compared and various error amplifier architectures explored. A method to optimize these amplifier architectures is also explored by means of Genetic Algorithms and Particle Swarm Optimization. Finally, stability measurement techniques for boost converters are explored and compared in order to gauge the viability of each method. The Middlebrook Method for measuring stability and cross-correlation are explored here

Mixed-source charger-supply CMOS IC

The proposed research objective is to develop, test, and evaluate a mixer and charger-supply CMOS IC that derives and mixes energy and power from mixed sources to accurately supply a miniaturized system. Since the energy-dense source stores more energy than the power-dense source while the latter supplies more power than the former, the proposed research aims to develop an IC that automatically selects how much and from which source to draw power to maximize lifetime per unit volume. Today, the state of the art lacks the intelligence and capability to select the most appropriate source from which to extract power to supply the time-varying needs of a small system. As such, the underlying objective and benefit of this research is to reduce the size of a complete electronic system so that wireless sensors and biomedical implants, for example, as a whole, perform well, operate for extended periods, and integrate into tiny spaces.Ph.D