Mickey Pierre Madsen

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.

Low Power Very High Frequency Switch-Mode Power Supply With 50 V Input and 5 V Output

This paper presents the design of a resonant converter with a switching frequency in the very high frequency range (30-300 MHz), a large step down ratio (ten times), and low output power (1 W). Several different inverters and rectifiers are analyzed and compared. The class E inverter and rectifier are selected based on complexity and efficiency estimates. Three different power stages are implemented; one with a large input inductor, one with a switch with small capacitances, and one with a switch with low on-resistance. The power stages are designed with the same specifications and efficiencies from 60.7-82.9% are achieved.

Very high frequency resonant DC/DC converters for LED lighting

This paper presents a very high frequency DC/DC converter for LED lighting. Several resonant topologies are compared and their usability discussed. At the end the resonant SEPIC converter is chosen based on the achievable power density and total bill of material. Simulations of a 51 MHz converter with 40 V input and 15 V output are made. The simulation shows possibility of achieving efficiency up to 87 % even with a HEXFET Power MOSFET. Three prototypes of the simulated converter are implemented showing good correlation with simulations. The prototypes have efficiencies up to 84 % and power densities up to 8.9 W/cm3 (146 W/in3).

Serogroups and antimicrobial susceptibility among Escherichia coli isolated from farmed mink (Mustela vison Schreiber) in Denmark.

Escherichia coli is commonly found in outbreaks of diarrhoea in mink during the production season although its role as a primary causal organism remains unclear. The present study was undertaken to determine the serogroups and antimicrobial susceptibility of E. coli isolates from healthy and diarrhoeic mink. Rectal swabs were taken from healthy and diseased animals, on six different farms, once at the onset of disease and again approximately 2 weeks later. The swabs were subjected to bacteriological investigation; a total of 210 E. coli were isolated, 98 from healthy animals and 112 from diseased. All isolates were serotyped and MICs were determined for nine antimicrobial compounds. Non-haemolytic isolates numbered 147, whereas 63 were haemolytic. Both haemolytic and non-haemolytic isolates were isolated from both healthy and diseased animals.A wide range of serogroups was detected, the most frequent being O2 (11.0%), O78 (11.0%), O153 (7.1%), O25 (5.7%), O6 (4.8%), and O15 (4.8%), but diarrhoea was not associated with specific serogroups. All isolates were sensitive to enrofloxacin, neomycin, gentamicin and colistin. In contrast, considerable variations in susceptibility were found among the six mink farms, for tetracycline (0-46.4%, average 21.9), ampicillin (2.9-50.0%, average 23.3), spectinomycin (8.0-35.7%, average 21.9), sulfamethoxazole (8.6-57.7%, average 30.0) and trimethoprim (0-35.7%, average 9.5). Resistance to tetracycline was statistically more prevalent among haemolytic than among non-haemolytic strains.In conclusion, serogrouping and haemolysin testing failed to identify any association with diarrhoeal disease and antimicrobial resistance was highly variable between different mink farms.

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.

On the ongoing 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 recent years in application of very high frequency (VHF) technologies in power electronics, describes the remaining challenges and shows results of the recent advances, among others a 120MHz, 9 W LED driver with 89 % efficiency.

Very high frequency half bridge DC/DC converter

This paper presents the first, off chip, class DE (resonant half bridge) converter working in the Very High Frequency (VHF) range. The benefits of using half bridge circuits both in the inverter and rectifier part of a VHF resonant dc/dc converter are analyzed and design equations for all components in the power stage are given. The circuit has been simulated to verify the accuracy of the presented equations and an efficiency of 89% has been shown. A prototype has been implemented with self-oscillating resonant gate drives driving the switches. The prototype has been used to drive an LED string and shows an efficiency of 85% at 29 MHz with 130 V input and 13.4 W output. The efficiency was above 82% in the range 110-150 V input with output power between 10.3 W and 16.5 W.

Low power very high frequency resonant converter with high step down ratio

This paper presents the design of a resonant converter with a switching frequency in the very high frequency range (30-300MHz), a large step down ratio and low output power. This gives the designed converters specifications which are far from previous results. The class E inverter and rectifier have been selected for the prototype and the circuits are analyzed and simulated. Three different power stages are implemented based on different design parameters. The first prototype is with a switch with small capacitances, the second one is with a switch with low on resistance and the last one is with a large input inductor. The power stages are designed with the same specs and efficiencies from 60.7-82.9% are achieved.

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.