Capacitance Minimization in Offline LED Drivers Using an Active-Ripple-Compensation Technique

This study proposes a novel approach for low-frequency output current ripple minimization in offline light-emitting diode (LED) drivers. This strategy is based on the large-signal modulation of the LED converter duty-cycle so that the output ripple can be reduced and, consequently, the required filtering capacitances of the converter can be somehow decreased. This technique is devised to be used on converters in which a single control loop is employed, such as offline integrated converters, where a single control loop is responsible to control the output current while maintaining the high power factor at the input (mains). The duty-cycle modulation is used to change the shape of the main waveforms of the converter, especially input and output currents. This allows for a reduction of the output current peak-to-peak ripple while the harmonic content of the input current is increased but kept within the limits imposed by the IEC standard. An application example for an integrated two-stage converter based on the cascade connection of two buck-boost converters is shown. Experimental results from a 70-W laboratory prototype supplied from a 115-V grid were carried out and compared with conventional approaches in order to verify the feasibility of the proposed technique.