Off-line LED driver for street lighting with an optimized cascade structure

This paper presents a converter structure applied to supply high power Light Emitting Diodes (LEDs) from the mains in a street lighting system, based on the Reduced Redundant Power Processing (R²P²) principle. To guarantee high power factor and low harmonic injection a buck-boost operating in Discontinuous Conduction Mode (DCM) is employed as Power Factor Corrector (PFC). The second converter of the structure controls the current over the LEDs string, but it does not process all the power. This is done summing the voltage of the first with the second converter. Avoiding the double processing of the power, the efficiency is improved. Besides that, the capacitance value of the first converter is dramatically reduced by increasing the ripple limits, making possible the use of film capacitors to increase the life span of the system. The system project and control structure are showed in details. A laboratory prototype, with a rated power of 75W for a rated input voltage of 220V_rms, was built to show the feasibility of the idea.