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

Embodiments of the subject invention pertain to a method and apparatus for contactless power transfer. A specific embodiment relates to an impedance transformation network, a new class of load network for application to a contactless power system. Embodiments of the impedance transformation network enable a contactless power system to operate without encountering the common problems of: 1) over-voltage and/or under-voltage conditions; 2) over-power and/or under-power conditions; 3) power oscillations; and 4) high heat dissipation.

Method and apparatus for contactless power transfer

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

This document describes several aspects relating to the design of dc-dc converters operating at frequencies in the VHF range (30–300 MHz). Design considerations are treated in the context of a dc-dc converter operating at a switching frequency of 100 MHz. Gate drive, rectifier and control designs are explored in detail, and experimental measurements of the complete converter are presented that verify the design approach. The gate drive, a self-oscillating multi-resonant circuit, dramatically reduces the gating power while ensuring fast on-off transitions of the semiconductor switch. The rectifier is a resonant topology that absorbs diode parasitic capacitance and is designed to appear resistive at the switching frequency. The small sizes of the energy storage elements (inductors and capacitors) in this circuit permit rapid start-up and shut-down and a correspondingly high control bandwidth. These characteristics are exploited in a high bandwidth hysteretic control scheme that modulates the converter on and off at frequencies as high as 200 kHz.

Design Considerations for Very High Frequency dc-dc Converters

This paper presents a resonant single-ended-primary-inductor-converter (SEPIC) converter and control method suitable for high frequency (HF) and very high frequency (VHF) dc-dc power conversion. The proposed design provides high efficiency over a wide input and output voltage range, up-and-down voltage conversion, small size, and excellent transient performance. In addition, a resonant gate drive scheme is presented that provides rapid startup and low-loss at HF and VHF frequencies. The converter regulates the output using an ON-OFF control scheme modulating at a fixed frequency (170 kHz). This control method enables fast transient response and efficient light-load operation while providing controlled spectral characteristics of the input and output waveforms. A hysteretic override technique is also introduced which enables the converter to reject load disturbances with a bandwidth much greater than the modulation frequency, limiting output voltage disturbances to within a fixed value. An experimental prototype has been built and evaluated. The prototype converter, built with two commercial vertical MOSFETs, operates at a fixed switching frequency of 20 MHz, with an input voltage range of 3.6-7.2 V, an output voltage range of 3-9 V, and an output power rating of up to 3 W. The converter achieves higher than 80% efficiency across the entire input voltage range at nominal output voltage and maintains good efficiency across the whole operating range.

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Anthony D. Sagneri

Papers

Opportunities and Challenges in Very High Frequency Power Conversion

Very-High-Frequency Resonant Boost Converters

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

Design Considerations for Very High Frequency dc-dc Converters

High-Frequency Resonant SEPIC Converter With Wide Input and Output Voltage Ranges