Jeppe Arnsdorf Pedersen

Evolution of Very High Frequency Power Supplies

The ongoing demand for smaller and lighter power supplies is driving the motivation to increase the switching frequencies of power converters. Drastic increases however, come along with new challenges, namely the increase of switching losses in all components. The application of power circuits used in radio frequency transmission equipment helps to overcome those. However, those circuits were not designed to meet the same requirements as power converters. This paper summarizes the contributions in the recent years in the application of very high frequency (VHF) technologies in power electronics, which show the results of the recent advances and describes the remaining challenges. The presented results include a self-oscillating gate drive, air-core inductor optimizations, an offline LED driver with a power density of 8.9 W/cm3, and a 120-MHz, 9-W dc powered LED driver with 89% efficiency as well as a bidirectional VHF converter. The challenges to be solved before VHF converters can be used effectively in industrial products are within those three categories: 1) components; 2) circuit architectures; and 3) reliability testing.

Self-oscillating resonant gate drive for resonant inverters and rectifiers composed solely of passive components

This paper presents a new self-oscillating resonant gate drive composed solely of passive components. The gate drive can be used in various resonant converters and inverters and can be used for both low and high side gate drive. The paper presents examples of how higher order harmonics can be used to improve the performance of the gate drive and how the gate drive can be implemented in a class E inverter, a class DE inverter and in class E inverter with a synchronous class E rectifier. The paper shows practical implementations of all the proposed inverters and converters operating in the Very High Frequency (VHF) range, all showing good results with peak efficiency up to 82% and output regulation from 70% to full load without bursting.

Self-oscillating galvanic isolated bidirectional Very High Frequency DC-DC converter

This paper describes a galvanic isolated bidirectional Very High Frequency (VHF = 30 MHz - 300MHz) Class-E converter. The reason for increasing the switching frequency is to minimize the passive components in the converter. To make the converter topology bidirectional the rectifier has to be synchronous. This increases the complexity of the gate drives, which in this paper is solved by using a self-oscillating gate drive. A bidirectional converter has been implemented and is described in this paper; the converter reaches efficiencies above 80% in forward conduction mode and 73.5% in reverse conduction mode. The designed converter operates at a switching frequency of 35.6 MHz, which is well within the VHF range. The same converter is also implemented with PCB embedded inductors to minimize cost and the physical volume of the total converter.

Investigation, development and verification of printed circuit board embedded air-core solenoid transformers

A new printed circuit board embedded air-core transformer/coupled inductor is proposed and presented. The transformer is intended for use in power converter applications operating at very high frequency between 30 MHz to 300 MHz. The transformer is based on two or more solenoid structures in different configurations. The different configurations are compared for usefulness as a transformer solution, and an analytical model of the inductive parameters for the most suitable configuration is derived for design purpose. The analytical model is verified by comparing calculations and measurements of prototypes. The analytical model shows good agreement with the measured results. The model can predict the inductive parameters of the transformer with a deviation range of approximately 3% to 22%. Lastly a prototype is used in a VHF converter to achieve a rise of 2.2% points in efficiency.

EMC Investigation of a Very High Frequency Self-oscillating Resonant Power Converter

This paper focuses on the electromagnetic compatibility (EMC) performance of a Very High Frequency (VHF) converter and how to lower the emissions. To test the EMC performance a VHF converter is implemented with a Class-E inverter and a Class-DE rectifier. The converter is designed to deliver 3 W to a 60 V LED, it has a switching frequency of 37 MHz and achieves an efficiency of 80%. For an LED driver to be used on the consumer market it has to fulfil the standard regarding EMC emissions. The conducted emission is often used as a reason to increase the switching frequency to the VHF range to avoid the regulations. This converter shows to be well below the levels for conducted emission even without filtering. For the radiated emissions the converter is above the limits without input and output filters. Several designs with different ways to lower the emissions are implemented and the different layouts and filtering are compared and discussed.

US mains stacked Very High Frequency self-oscillating resonant power converter with unified rectifier

This paper describes a Very High Frequency (VHF) converter made with three Class-E inverters and a single Class-DE rectifier. The converter is designed for the US mains (120 V, 60 Hz) and can deliver 9 W to a 60 V LED. The converter has a switching frequency of 37 MHz and achieves an efficiency of 89.4%. With VHF converters the power density can be improved and the converter described in this paper has a power density of 2.14 W/cm3. The power factor (PF) requirements of mains connected equipment is fulfilled with a power factor of 0.96.