Bernd Ackermann

Design method and material technologies for passives in printed circuit Board Embedded circuits

The integration of passive components into the printed circuit board (PCB) as embedded passives integrated circuits (emPIC) results in a higher power density of power converters. To achieve a highly automated, low cost, integral manufacturing, the devices are constructed layer wise. Materials and processes necessary for the manufacturing of such circuits are described in this publication. Especially for magnetic components like inductors and transformers the design of such thin components is challenge. Because of the high aspect ratio, traditionally used models lead to a high calculation effort or use nonappropriate approximations. This contribution presents an analytic approach for the design. The model considers the magnetic flux distribution in the core and in the winding area and therefore allows a precise calculation of the inductivity as well as the losses in the device and their distribution. It is very well suited for a parametric analysis and thus for the synthesis of thin planar magnetic components. Material technologies for the construction of the capacitive layers and the magnetic cores are investigated. A ferrite polymer compound is adapted to be compatible with the PCB laminating process. Accordingly a 60-W offline converter was designed and fabricated using the new technology. Its transformer is entirely integrated in the PCB as well as 11 capacitors. Standard PCB lamination processes are used for the layerwise integration of the components. The circuit needs an area of the size of a credit card with a PCB thickness of 4 mm. Up to 82% efficiency could be demonstrated.

Control of LEDs

There is a strong interest in using LEDs for general illumination due to the potential they offer for energy saving, environmental friendliness, new opportunities in lighting design, and control of the intensity, color, and spatial distribution of light. General illumination requires primarily white light that can be obtained by mixing e.g. the light of red, green, and blue LEDs. This enables also color adjustability, which is considered to be a most attractive feature of future LED lamps. There is common consent that when using color mixing some kind of feedback control must be applied in order to meet color accuracy requirements. In this paper color control concepts are briefly reviewed and control of a lamp with more than 4 primary LED colors is reduced to the known control of 3 primary LED colors. Measurements are provided for the temperature dependence of LED and color sensor characteristics. Color control implementation is outlined using a laboratory setup based on a rapid color control prototyping system which uses commercially available software and digital hardware amended by custom in-house developed hardware. The rapid control prototyping system is applied to control the color of an experimental RGB LED lamp

Analytical modelling of winding capacitances and dielectric losses for planar transformers

Efficient and sufficiently accurate analytical models are valuable tools for the design of planar magnetic components. This paper describes a new analytical model of winding capacitances and dielectric losses for planar transformers. It is compared qualitatively with a more simple model valid for wire wound components and validated against measured capacitances of some prototypes. The new model can be used to optimize the design of planar magnetic components. Optimizing the thickness of the insulation layers between the copper layers of a planar winding is shown as an example.

Single phase induction motor with permanent magnet excitation

A permanent magnet excited single-phase induction motor (SIM) has a very simple mechanical structure. Its stator is similar to that of shaded-pole or single-phase synchronous motors. However, there are two rotors: a diametrically magnetized permanent magnet cylinder rotating freely that is mounted within a copper cup linked to the load. Field equations describing its stationary behavior are solved analytically for a simplified motor geometry. From these performance characteristics are calculated and compared with measurements. Guidelines for design optimizations are derived.

On high frequency high voltage generators with planar transformers

The purpose of this paper is to study the feasibility of a resonant high voltage generator using a high voltage planar transformers. The emphasis is on improving the power density, efficiency, reliability, and repeatability of component characteristics of the planar high voltage transformer by a novel planar winding design. Converter and transformer design issues are discussed and a prototype is evaluated experimentally.