Optimum Injected Current Harmonics to Minimize Peak-to-Average Ratio of LED Current for Electrolytic Capacitor-Less AC–DC Drivers

The lifetime of an ac-dc LED driver can be increased by eliminating the electrolytic capacitor. Unfortunately, it results in pulsation with twice the line frequency in the driving current. Injection of the third and fifth harmonics into the input current can reduce the peak-to-average ratio of the driving current, which is beneficial for reliable operation of the LEDs. This letter discusses the relationship between the peak-to-average ratio and the injected harmonics, and the optimum injected third and fifth harmonics to minimize the peak-to-average ratio are obtained, while ensuring that the input power factor is higher than 0.9 to meet the regulatory requirement such as the ENERGY STAR. This optimum injected current harmonics is verified by a flyback-based electrolytic capacitor-less LED driver with 25 V, 0.35 A output.