Dirk Hente

Driver Electronics for LEDs

Large-volume applications of high-brightness LEDs are well established for signaling and signage. They are expected to replace conventional lamps in automotive applications in the near future and incandescent, halogen and fluorescent lamps at least in some general illumination applications within a few years. Innovative driver circuits optimized with respect to functionality, efficiency, cost, size and reliability are an enabler for the successful introduction of new LED based lighting products. This paper consists of two parts. In the first part, the influence of the LED current waveform, which depends on the driver topology and control, on the luminous flux and hence, the luminous efficiency is investigated experimentally for different LEDs, i.e. a red, a green and a blue 1 W LED. In the second part, an LED driver with PCB integrated capacitive layers and a transformer made of ferrite polymer compound having an extreme high power density is presented. This driver uses highly integrated passive components. This new concept is named emPIC (embedded passives integrated circuit). All passive components will be integrated in the printed circuit board (PCB) using structured layers of different materials. Experimental results taken from the driver demonstrate that the LED current ripple stays within the margins defined in the first part of this paper

Drivers for OLEDs

Organic light emitting diodes (OLEDs) are expected to become important light sources in the future. In contrast to point source inorganic LEDs, OLEDs are large area device. This in combination with different materials results in differences in performance and electrical behaviour, which on their turn result in different drivers. This work gives an overview of OLED characteristics. Based on these characteristics a simplified equivalent circuit is obtained and driver requirements are derived. It is found that AM dimming is preferred. Additionally, some OLED characteristics are compared with those of inorganic LEDs.

Dynamic Control Point Simulation of OLEDs

Organic light emitting diodes (OLEDs) for lighting applications are still in a research phase, but improvements are made continuously. In the last years, colour variable OLEDs have been reported by research. For the design of drivers and control systems for colour variable OLEDs, it is important to have accurate models to reduce the development costs of these components. In this work, a simulation method is proposed. Although the model uses statically measured input data, it is possible to model dynamic waveforms very accurately. This work gives an overview of colour variable OLED characteristics. The proposed model is presented and its results are compared to experimental results.