PELD - Printed Electro-Luminescent Driver

Electro-luminescent elements are used as background lightning for e.g. displays in mobile phones. An electro-luminescent driver is a device which is used to control the colour and the brightness of the electro-luminescent foil respectively. Through changing the input frequency and amplitude of the foil, different colours and intensities can be realised. The driver itself generates a high ac-voltage from a low dc-voltage like from small printed batteries. The circuit of the Printed Electro-Luminescent Driver (PELD), in order to be printable, has to include only passive and active elements which can be printed at this time. Therefore resistances, capacitances and inductances have been designed and characterized. The PELD is designed to drive a 5cm2 light emitting foil. For the implementation, the circuit of the driver, has been split in different parts, namely in a frequency/signal generation which generates the desired frequency with a relative small amplitude (to reduce the losses), and an output-stage where the ac-voltage is generated. Together the whole design needs only four additional transistors (which at the moment cannot be printed). In contrast to conventional drivers the implemented circuit is more efficient, because the leakage current is extremely reduced and through printing the production – time is also reduced. Without any external supply, the needed batteries can also be printed, the PELD can be used for lighting different fonts, parts of pictures and backgrounds. The entire driver circuit without the additional bipolar transistors can be printed by screen printing. In the test of the device after production certain characters in certain fonts as well as background lightning of the produced 5cm2 lightning area have been realized.