A flicker-free electrolytic capacitor-less ac-dc LED driver

Electrolytic capacitor is the key component that limits the lifetime of LED driver. When an ac-dc LED driver with the function of power factor correction (PFC) outputs a pulsating current to drive LEDs, electrolytic capacitor is not required any longer. However, the pulsating current brings flicker with twice the line frequency. In this paper, the concept of flicker-free electrolytic capacitor-less ac-dc driver for LED lighting is proposed, which consists of an electrolytic capacitor-less PFC converter and a bidirectional buck/boost converter. The bidirectional buck/boost converter provides the path for the ac component in the pulsating current of the PFC converter to flow through, leaving a pure dc current to drive the LEDs without flicker. The voltage of the output filter capacitor of the bidirectional converter is intentionally designed to have large ripple, and thus the capacitance can be greatly reduced. Consequently, the output filter capacitor can adopt film capacitor instead of electrolytic capacitor. So the ac-dc LED driver has no flicker and has a long lifetime. A 48 V, 0.7 A output prototype is built and tested in the lab, and the experimental results are presented to verify the effectiveness of the flicker-free electrolytic capacitor-less ac-dc LED driver.