A simple cost-effective PSR LED driver without auxiliary winding

Abstract

A simple cost-effective LED driver based on the primary-side-regulation (PSR) scheme without auxiliary winding is proposed and designed. The driver operates in discontinuous conduction mode (DCM). By means of controlling the discharging and charging of an internal timing capacitor, the conduction time T_{on_s} of the secondary-side current is monitored and the ratio of T_{on_s} to the switching period T_s is kept constant, resulting in a constant output current. The output current zero cross detecting (ZCD) signal is sensed by the negative change of power MOSFET's source voltage due to the resonance of the primary winding with the parasitic capacitor C_dss of MOSFET. The driving IC and 650V power MOSFET chips are packaged together in SOP-8. The proposed driver is implemented with few external components and its size is minimized. Experimental results show that the current variation is within ±3%, and the efficiency exceeds 80% at the output power of 3-5W under universal input voltage.