A simple digital current controller for solid-state lighting

During the last two decades, the performance of solid-state lighting devices, such as light emitting diodes (LEDs) and organic LEDs (OLEDs) has improved rapidly. Hence, LEDs and OLEDs become very attractive for many applications. (O)LEDs are preferably current driven, because the relationship between current and luminance is linear. Typically, the implemented control algorithms are analog. This paper proposes the use of a very simple though extremely stable digital control algorithm, which enables the replacement of expensive "driver control" ICs by simple and cheap comparator ICs. Hence, the costs of the system can be reduced. Additionally, the system shows very high efficiency as well as a very high dynamic performance. The digital control method is characterized by the following features: - The control strategy is extremely easy to implement. - The control strategy eliminates the need for (expensive) converter control ICs. - System costs are reduced. - The control strategy is extremely robust, i.e. the control is stable. - The control offers a high dynamic response. - The switching frequency is not constant, but its maximum value is limited. - In most points of operation, subharmonic currents are generated by the controller, which may result in flicker effects. Nevertheless, if designed correctly, the sub harmonics can be avoided. - The control method is extremely suitable for buck converters, but can also be applied to other topologies.