LED driver with bidirectional series converter for low frequency ripple cancelation

This paper deals with a topology for an off-line LED electronic driver. The use of electrolytic capacitors in the DC link is avoided, therefore extending lifespan and reliability. Given that the resulting output capacitance of the PFC stage is relatively small, a high LF ripple appears at the DC-link. This work proposes the use of a current-fed bidirectional buck converter as a second stage. With the proposed scheme, this stage processes only the AC power corresponding to this voltage ripple, thus increasing the efficiency with respect to a conventional two stage topology. In this approach, the output converter is connected in series with the LEDs assembly, yielding to low voltage stresses at the stage. With a given current control, this scheme ensures a constant current through the LEDs, and ability for AM and PWM dimming operation. A design procedure is shown, and the theoretical results have been validated in a built prototype for a 65W LEDs lamp.