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 power converter nearly losslessly delivers energy and recovers energy from capacitors associated with controlled rectifiers in a secondary winding circuit, each controlled rectifier having a parallel uncontrolled rectifier. First and second primary switches in series with first and second primary windings, respectively, are turned on for a fixed duty cycle, each for approximately one half of the switching cycle. Switched transition times are short relative to the on-state and off-state times of the controlled rectifiers. The control inputs to the controlled rectifiers are cross-coupled from opposite secondary transformer windings.

High efficiency power converter

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. >

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

A self-oscillating power converter utilizes a MOSFET power transistor switch with its output electrode coupled to a tuned network that operatively limits the voltage waveform across the power switch to periodic unipolar pulses. The transistor switch may be operated at a high radio frequency so that its drain to gate interelectrode capacitance is sufficient to comprise the sole oscillatory sustaining feedback path of the converter. A reactive network which is inductive at the operating frequency couples the gate to source electrodes of the transistor switch and includes a variable capacitance as a means of adjusting the overall reactance, and hence the converter's switching frequency in order to provide voltage regulation. A resonant rectifier includes a tuned circuit to shape the voltage waveform across the rectifying diodes as a time inverse of the power switch waveform.

Self-oscillating high frequency power converter

A transformer in combination with a push-pull transistor switch forms the inverter of a DC to DC converter. Feedback from the rectified output of the transformer ferroresonant winding controls the inverter frequency. A controllable current source responsive to a signal derived from the converter output voltage controls the charging of a timing capacitor which, upon reaching a threshold value, causes termination of each inverter half-cycle. A capacitor discharge arrangement is included to ensure continuity of inverter frequency under light load conditions when inverter half-cycle termination results from transformer saturation.

Ferroresonant power converter with controll of inverter frequency and sensing of saturation condition

Each of a plurality of parallel power supplies is connected to a common load via a coupling diode. The voltage across the coupling diode is monitored as well as the peak conducting voltage across the supply rectifier devices. A comparator is responsive to the monitored coupling diode voltage exceeding the monitored rectifier device conducting voltage to produce an alarm signal indicative of the supply not being coupled to the common load through the coupling diode.

Weyman B. Suiter

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

Self-oscillating high frequency power converter

Ferroresonant power converter with controll of inverter frequency and sensing of saturation condition

Rectifier monitoring circuit