THIS paper explores opportunities and challenges in power conversion in the VHF frequency range of 30-300 MHz. The scaling of magnetic component size with frequency is investigated, and it is shown that substantial miniaturization is possible with increased frequencies even considering material and heat transfer limitations. Likewise, dramatic frequency increases are possible with existing and emerging semiconductor devices, but necessitate circuit designs that either compensate for or utilize device parasitics. We outline the characteristics of topologies and control methods that can meet the requirements of VHF power conversion, and present supporting examples from power converters operating at frequencies of up to 110 MHz.

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Opportunities and Challenges in Very High Frequency Power Conversion

This paper presents a resonant boost topology suitable for very-high-frequency (VHF, 30-300 MHz) DC-DC power conversion. The proposed design features low device voltage stress, high efficiency over a wide load range, and excellent transient performance. Two experimental prototypes have been built and evaluated. One is a 110-MHz, 23-W converter that uses a high-performance RF lateral DMOSFET. The converter achieves higher than 87% efficiency at nominal input and output voltages, and maintains good efficiency down to 5% of full load. The second implementation, aimed toward integration, is a 50-MHz, 17-W converter that uses a transistor from a 50-V integrated power process. In addition, two resonant gate drive schemes suitable for VHF operation are presented, both of which provide rapid startup and low-loss operation. Both converters regulate the output using high-bandwidth, on-off hysteretic control, which enables fast transient response and efficient light-load operation. The low energy storage requirements of the converters allow the use of aircore inductors in both designs, thereby eliminating magnetic core loss and introducing the possibility of easy integration.

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Very-High-Frequency Resonant Boost Converters

A limitation of many high-frequency resonant inverter topologies is their high sensitivity to loading conditions. This paper introduces a new class of matching networks that greatly reduces the load sensitivity of resonant inverters and radio frequency (RF) power amplifiers. These networks, which we term resistance compression networks, serve to substantially decrease the variation in effective resistance seen by a tuned RF inverter as loading conditions change. We explore the operation, performance characteristics, and design of these networks, and present experimental results demonstrating their performance. Their combination with rectifiers to form RF-to-dc converters having narrow-range resistive input characteristics is also treated. The application of resistance compression in resonant power conversion is demonstrated in a dc-dc power converter operating at 100MHz

Resistance Compression Networks for Radio-Frequency Power Conversion

This paper presents a new switched-mode resonant inverter, which we term the inverter, that is well suited to operation at very high frequencies and to rapid on/off control. Features of this inverter topology include low semiconductor voltage stress, small passive energy storage requirements, fast dynamic response, and good design flexibility. The structure and operation of the proposed topology are described, and a design procedure is introduced. Experimental results demonstrating the new topology are also presented. A prototype inverter is described that switches at 30 MHz and provides over 500 W of radio frequency power at a drain efficiency above 92%. It is expected that the inverter will find use as a building block in high-performance dc-dc converters among other applications.

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A High-Frequency Resonant Inverter Topology With Low-Voltage Stress

A new type of high-frequency high-efficiency resonant DC/DC converter is proposed, analyzed, and verified experimentally. It is called a class-E converter because it consists of a class-E inverter and a class-E rectifier. The class-E rectifier acts as an impedance inverter and is compatible with the class-E inverter. Consequently, the converter can operate with load resistances from a full load to infinity while maintaining zero-voltage switching of the transistor in the inverter and the diode in the rectifier. It operates safely with a short circuit at the output. Because of a high value of the load quality factor Q/sub 1/, a narrow frequency range suffices to regulate the DC output voltage over the whole load range. The measured relative bandwidth was delta f/f/sub min/=42.2% as the load resistance was varied from 70 Omega to open circuit. The measured efficiency at the full load was 89% with a 9 W output power at 1 MHz. A family of class-E/sup 2/ resonant DC/DC power converters is given. The possibility of reduction of class-E/sup 2/ converters to lower-order resonant and pulse-width-modulation converters is shown. >

Resonant DC/DC converter with class-E inverter and class-E rectifier

A family of rectifiers suitable for operation at high frequencies is presented. These rectifiers use naturally occurring component parasitics to control diode switching thereby minimizing parasitic ringing and improving rectification efficiency by reducing the flow of harmonic currents. The input impedance of the resonant rectifier is linear, which makes possible an accurate adjustment of the rectifier to present the proper load impedance to an inverter. When a resonant rectifier is coupled to a resonant inverter in this manner, a fully resonant DC-to-DC converter is produced. With these circuits it is possible to achieve a very low input/output ripple and EMI since voltages and currents seen by the filters are confined to a very narrow frequency range compared to conventional squarewave converters. >

A new family of resonant rectifier circuits for high frequency DC-DC converter applications

An experimental DC-to-DC converter prototype based on a zero-voltage switching, resonant circuit topology is described. The converter is suitable for mounting directly on a circuit card. The unit provides a regulated 5 V output at power levels up to 50 W with an input between 40 and 60 V. The switching frequency is between 20 and 24 MHz, depending on the input voltage and load. Differential input and output ripple and EMI are extremely low and somewhat difficult to measure. The converter prototype has been designed to demonstrate compatibility with a fully automated assembly process based on surface-mount technology. Solutions are presented to a number of problems, including MOSFET gate-drive and rectifier diode capacitance, that have seriously limited the performance of high-frequency converters operating with useful input and output voltages. >

F.T. Dickens

Papers

A new family of resonant rectifier circuits for high frequency DC-DC converter applications

A resonant DC-to-DC converter operating at 22 megahertz