Wojciech A. Tabisz

Zero-voltage-switching multi-resonant technique-a novel approach to improve performance of high frequency quasi-resonant converters

The power transistor in zero-current-switched quasiresonant converters (ZCS-QRCs) suffers from excessive voltage stress, and the converter regulation characteristics and stability are adversely affected by parasitic oscillations caused by the junction capacitance of the rectifying diode. A novel, multiresonant switch concept is proposed to overcome these problems. A unique multiresonant network arrangement results in absorption of all parasitic components, including transistor output capacitance, diode junction capacitance, and transformer leakage inductance, in the resonant circuit. This results in favorable switching conditions for all devices. Experimental results show that ZVS multiresonant converters are superior to ZVS-QRCs due to reduced transistor voltage stress and improved load range and stability.<<ETX>>

Present and future of distributed power systems

The current stage of development of distributed power systems is presented. Various DC-bus and AC-bus distributed power system architectures are discussed. System integration issues related to paralleling and cascading of DC/DC converters are explained. Benefits and challenges of distributed power systems in various applications are summarized.<<ETX>>

A MOSFET resonant synchronous rectifier for high-frequency DC/DC converters

A resonant synchronous rectifier which combines the fast switching of Schottky diodes with low conduction drop of MOSFET devices is discussed. The MOSFET devices are driven in a resonant fashion by the power circuit, resulting in partial recovery of the energy stored in the parasitic capacitances. Power loss in the resonant synchronous rectifier is determined as a function of various devices parameters and switching frequency. Contributions of conduction losses, gate-drive switching losses, and losses due to current circulating in the parasitic capacitances are discussed. The analysis indicates that, at megahertz range switching frequencies, a resonant synchronous rectifier has a significantly higher efficiency than either a PWM (pulse width modulation) synchronous rectifier or a Schottky diode rectifier.<<ETX>>

Zero-voltage-switched quasi-resonant buck and flyback converters-experimental results at 10 MHz

Experimental results of buck and flyback zero-voltage-switched quasi-resonant converters (ZVS-QRCs) operating above 5 MHz are presented. A design procedure is presented that minimizes voltage stress to the transistor while maintaining zero-voltage-switching for all loads. A novel, quasi-resonant gate drive scheme is proposed and implemented in a buck converter. The drive is simple and provides high switching speed. Power dissipation in the gate drive is substantially reduced due to the quasi-resonant operation. Due to a much reduced switching losses, dv/dt, and di/dt, the ZVS-QRCs are particularly suitable for very-high-frequency distributed power supply applications.

Zero-voltage-switching technique in high-frequency off-line converters

Zero-voltage switching (ZVS) is implemented using a half-bridge (HB) topology for high-frequency offline applications. Two ZVS techniques are discussed: one is a quasiresonant technique (QRC) the other a multiresonant technique (MRC). A breadboarded HB ZVS-QRC is presented which operates from a 300+or-50 V input with maximum output power of 75 W (5 V, 15 A) and an efficiency of 83.5% at low line and full load and 79.2% at high line and full load. In ZVS-MRCs, all semiconductor devices are operated with no abrupt changes of the voltage across the devices. The technique permits utilization of junction capacitances of all semiconductor devices and the transformer leakage inductance to form a multiple-resonant-tank network to implement zero-voltage switching for all semiconductor devices. Employing this technique, a HB ZVS-MRC is breadboarded with the same specifications as the HB ZVS-QRC. The efficiency of the HB ZVS-MRC is slightly lower than that of the HB ZVS-QRC, 81.7% at full load and low line and 78.5% at full load and high line.<<ETX>>

Zero-voltage-switched quasi-resonant buck and flyback converters — Experimental results at 10 MHz 1

Experimental results of buck and flyback zero-voltage-switched quasi-resonant converters (ZVS-QRCs) operating above 5 MHz are presented. A design procedure is presented that minimizes voltage stress to the transistor while maintaining zero-voltage-switching for all loads. A novel, quasi-resonant gate drive scheme is proposed and implemented in a buck converter. The drive is simple and provides high switching speed. Power dissipation in the gate drive is substantially reduced due to the quasi-resonant operation. Due to a much reduced switching losses, dv/dt, and di/dt, the ZVS-QRCs are particularly suitable for very-high-frequency distributed power supply applications.

Miniaturized power converters for smart-structure applications

One definition of a smart structure is a structure with a miniaturized control system embedded in or attached to the material for improved performance of the structure. The feasibility of embedding piezoelectric sensors and actuators has been demonstrated. Current research is focusing on the development of the support electronics for these sensors and actuators. In this paper we discuss miniaturized power conversion/amplifier electronics for these actuators suitable for these smart structure applications. State-of-the-art dc to dc power converters with a 2 square inch footprint and a 1/4 in profile with power densities up to 50 W/in3 with efficiencies above 80% are described. The power converters to minimize thermal dissipation. The power bus requirements are also discussed.

Distributed power systems—benefits and challenges

Distributed power systems are replacing centralized power systems in many applications where higher distribution efficiency, better load regulation, increased flexibility, maintainability, redundancy, and better power and heat management are the primary considerations. The main challenges of distributed power systems are related to system integration, design of high-density, high-efficiency point-of-load DC/DC conveners, and cost-effectiveness. Various distributed power systems, including both DC and AC bus architectures are discussed.