Kosala Gunawardane

Development of browne's arc model for HTS applications

This paper presents the development of an electrical arc model that can be used for various applications of High-Temperature Superconductor (HTS). The limitations of the conventional arc models for HTS application are briefly discussed. The scope of further development for Brownes Arc model for HTS application is identified. An improved arc model will have several benefits while assessing performance for various HTS applications. Digital simulation studies are conducted to show the arc characteristics under the high current condition for future development.

Design of an efficiency improved dual-output DC-DC converter utilizing a supercapacitor circulation technique

The Supercapacitor Assisted Low Dropout Regulator (SCALDO) is a novel approach to achieving high end-to-end efficiency (ETEE) in linear, step-down, DC-DC converters. This is a patented technique and it has been well established with various proof-of-concept prototypes showing its efficiency advantage in the range of a factor of 1.33 to 3 along with the other excellent linear characteristics such as low noise and high slew rate. As a better way of utilizing this approach to match multiple voltage rail applications such as mobile battery operated products, processor-based systems, automotive systems, and data centers, a further extension to the technique called Dual-Output Supercapacitor Assisted Low Dropout Regulator (DO-SCALDO) has been suggested. In this paper, the design approach and the practical implementation details of a prototype version of 5V-to-dual 1.8 V DO-SCALDO are discussed.

Loss estimation and validation of the SCALDO implementation

A low frequency supercapacitor circulation technique coupled with a commercial low dropout regulators(LDO), namely the supercapacitor assisted LDO (SCALDO), can achieve significantly high end-to-end efficiency(ETEE) for linear regulators. The ETEE could be closer to the efficiencies of practical switching regulators, but without having the negative aspects of switching regulators such as RFI/EMI issues and the use of bulky inductors. In these supercapacitor assisted linear regulator topologies, the efficiency improvement compared to linear regulators is given by a special figure of merit, efficiency improvement ratio, which can be in the range of 1.33 to 3 depending on the SCALDO configuration. Compared to the six different possible loss elements in a switching regulator, in the SCALDO technique losses are mainly contributed by equivalent series resistance of the supercapacitor, RDS (on) of the switches, parasitics in the PCB traces and losses due to paralleling of the supercapacitor with a small buffer capacitor in addition to the losses of the LDO stage. This paper presents a Laplace transform-based analytical solution to estimate the losses during the four phases of SCALDO technique with an example for a 12V-to-5V SCALDO converter.

Single-input, dual polarity, dual output DC-DC converter implementation based on the SCALDO technique

Supercapacitor assisted low dropout regulator (SCALDO) is a new approach to designing high-efficiency DC-DC converters by combining supercapacitors and a commercial LDO. In this approach, the end-to-end efficiency of the converter is increased by a multiplication factor, in the range of 1.33 to 3, compared with the efficiency of a linear regulator circuit with the same input-output voltages. SCALDO technique can be extended to develop a dual polarity, dual output version suitable for powering portable products, with efficiencies comparable with switching converter combinations giving dual polarity outputs. In this paper, theoretical background and the conceptual design of the proposed converter are discussed. As a proof of concept 12 V to ±5 V DC-DC converter is implemented and its efficiency, load regulation, and line regulation details are presented.

Back-to-back MOSFET switches to reduce the losses in SCALDO implementation

In todays portable devices, major DC-DC topologies are mixed and matched to provide multiple DC rails to power point of load (POL) rails. The traditional high frequency DC converter approaches to achieve high efficiency have their strengths and draw backs, and none of them could be considered ideal solution to energy efficiency and battery run time issues of modern portable devices. Supercapacitor assisted low dropout regulators (SCALDO) is a novel linear regulator topology developed by combining an array of supercapacitors, an LDO and a very low frequency switching arrangement to achieve high efficiency in linear converter comparable with high frequency switching converters. The technique implemented in commonly used DC-DC converter stages such as 12–5V, 5–3.3 V and 5–1.2 V with efficiency improvement factors of 2, 1.33 and 3 respectively, with the example of increasing the 42% efficiency of a 12–5 V linear converter to 84% theoretically. In these early prototype versions, solid state relays were used as the low frequency switches to eliminate the unnecessary discharging of the supercapacitors (SC), however, high on resistance in these switches increase the switch losses. This paper provides the details of a new design technique to eliminate this SC discharge issue and to further reduce the switch losses by using back-to-back MOSFET switches, together with performance details of 12–5 V practical converter.

Design concepts and preliminary implementations of dual output supercapacitor-assisted low-dropout regulators (DO-SCALDO)

Supercapacitor-assisted low dropout regulators (SCALDO) technique has been developed to improve the end-to-end efficiency of linear regulators by factor of 1.33 to 3. In this approach, a low frequency supercapacitor circulation stage is combined with a commercial LDO to achieve the overall efficiency improved design. After successful implementation of various SCALDO prototypes, practically useful further improvements for original concept were considered. Dual output (DO-SCALDO) has been suggested as an improvement to provide two output levels in a single design while maintaining the useful hallmarks of the original SCLADO approach. The new improvement: the DO-SCALDO technique, can generate dual output levels which are same or different. A circuit prototype of a 7V-to-dual-1.5 V DO-SCALDO was built and tested to prove the concept and summary of results are presented.