A Two-stage Electrolytic Capacitor-less AC-DC LED Driver

AC-DC LED driver converts a commercial ac voltage to a steady dc voltage and produceconstant current for driving LED. Electrolytic capacitor should be removed to improve the lifetimeand reliability of the LED driver. The thesis is dedicated to the design of a two-stage electrolyticcapacitor-less AC-DC LED driver.The two-stage LED driver consists of a power factor correction (PFC) converter and a dc-dcconverter in cascaded. The PFC converter converts a commercial ac voltage to a steady dc voltage,and the dc-dc converter converts the dc voltage produced by the PFC converter to a steady dc currentfor driving LED. In this thesis, the boost converter is adopted for the PFC converter. The storagecapacitor voltage ripple is intentionally increased to significantly reduce the value of the storagecapacitor, so that film capacitor can be adopted to replace electrolytic capacitor, and thus the lifetimecan be increased. The minimum, maximum and average value of the storage capacitor voltage as afunction of the storage capacitance are derived so as to ensure the boost PFC converter operatesnormally in the whole input voltage range. The determination of the storage capacitance is alsodiscussed. The boost PFC converter is operated in critical current mode, so that the power switchachieves zero-current-switching (ZCS) and the reverse recovery of the boost diode is avoided. Thehalf-bridge series resonant converter is chosen as the dc-dc converter, and it is operated indisconstinous current mode. Such operation not only achieves ZCS for the power switches andrectifier diodes, but also exhibit the characteristic of constant output current, which is deem fordriving LED. The operating principle of the two-stage electrolytic capacitor-less AC-DC LEDdriver is analyzed in details, the parameter design of the power stage is discussed, and the controlstrategy of is also presented.A60W prototype has been built and tested in the lab, and the experimental results verify theeffectiveness of the proposed two-stage electrolytic capacitorless AC-DC LED driver.