Static losses and controllability of current fed dimmable LED drivers

The paper presents synthesis and comparison of several drivers of original topologies for LED dimming. The work is based on the hypothesis that the direct current control, in contrast to indirect voltage control, is very useful in LED applications where luminous flux is almost proportional to LED´s current. In order to confirm or disprove this hypothesis, several current fed LED ballasts have been synthesized based on corresponding voltage fed converters and known rules of their transformation. The synthesized circuits are mathematically described and experimentally tested. The obtained results show that the approach is useful from the point of view of controllability of LED lamp. Special attention is paid to the estimation of static losses of the LED drivers presented in the given paper. It is concluded that although these parameters are not as good as for voltage fed drivers they remain on an acceptable level. Finally, it is concluded that the current fed step-down driver is advantageous from many points of view and it is worth to work on its further improvement. At the same time, some practical difficulties of implementation of the current fed converters have been detected. This, first of all, regards to the lack of the natural current sources and the risk of their open loop operation. These problems, however, are subject of future works.