Advanced System Technology branch AST of Fraunhofer IOSB
Brief description of the project
In this project, the possibility was created to drive multi-channel (>4 channels) UVC LED modules with high precision without residual ripple and to make them suitable for use in measuring devices. By combining linear regulators at the cathode terminal and switching regulators at the anode terminal in a common driver design, it was possible to combine the advantages from both driver worlds (high efficiency, almost no ripple of the LED current, low heat generation) and to eliminate the disadvantages of both driver topologies as far as possible. Based on the use of highly integrated components, an LED driver has thus been developed in which only 2 cm² of space is required per channel to drive up to 1000 mA at a flux voltage of up to 16 V. With double-sided assembly, a further reduction in the required area would be possible. The system is scalable and can be expanded up to 16 channels per unit.
By including a photodiode on the submount, accurate detection of the radiation intensity of each LED is possible. It uses the photodiode's characteristic curve to control the intensity of each LED via its current. Decreases in output due to aging can thus be detected and compensated for within certain limits.
The aluminum reflector developed in the project, which was largely developed by project partner OSA OptoLight GmbH, collects and shapes the (UV) LED light. The downstream microlens array made of quartz glass mixes the different wavelengths with only a slight increase in divergence.
Three demonstrators have been developed and manufactured several times in the project, which are available on demand to the partners of the AUVL consortium. The demonstrators offer good optical properties and allow the consortium partners to use up to six different LED wavelengths. The bus-capable demonstrators can be extensively controlled via the developed software or, with the help of the disclosed and documented communication protocol, also via own software solutions. Up to 242 devices, each with 6 LED channels, can be controlled on the RS485 bus, which is up to 1.2 km long. By means of broadcast messages implemented in the protocol, commands can also be sent to all connected devices simultaneously.
Project goals
The task of Fraunhofer IOSB-AST in the research network was to develop a ripple-free multi-channel LED driver and to build several demonstrators for different application purposes. The elimination of ripple could be realized by combining a highly efficient switching regulator and a downstream linear regulator. The LEDs are continuously dimmable in the range of 0-100%, whereby a high precision of the irradiance for measurement tasks could be achieved.
