Reasearch In Single Stage Electrolytic Capacitor-less AC/DC LED Driver

As the energy crsis problem become more and more serious, lighting is an important aspect of the energy consumption, so decrease the lighting consumption will decrease the whole energy consumption in the world. Lighting emitting diode(LED) which is a new type green solid cold light souce, has many advantages such as high efficiency, energy saving, environmental friendliness, safety and long lifetime over traditional lighting source. And the technology of LED develops rapidly recently. Meanwhile, the evolution of high reliable, high input power factor, long lifetime and low cost LED drivers is inevitable. In this paper, an electrolytic capacitor-less LED driver is studied.For the LED driver which utilizes the utility grid, power factor correction(PFC) control should be employed. When input power factor is unity, the input current is forced to be in phase with input voltage, leading a pulsating input power, while constant output power is required due to the driving characteristics of LED. Thus, a storage capacitor with large capacitance is demanded for handling the instantaneous power difference. Electrolytic capacitors are widely used as the storage capacitor. However, the lifetime of electrolytic capacitors is far less than the LED devices, which reveals the need for eliminating the electrolytic capacitors in LED drivers.So this paper proposes a single-stage electrolytic capacitor-less LED driver which pluses an auxiliary winding in the transformer and an additional full-bridge circuit to Flyback converter. It transfers the unbalance energy to auxiliary capacitor through auxiliary circuit. Smaller capacitance is utilized with large voltage ripple for energy storage instead of large capacitance with small voltage ripple. Thus electrolytic capacitors can be replaced by film capacitors. This paper gives the detailed operation principles of the proposed LED driver. Then this paper deduces the relationship between the ripple voltage across the auxiliary capacitor and the capacitance of it. What’s more, the primary inductor of the transformer is also inferred. Then the control strategy of the proposed LED driver is given and the simulation result is performed.At last, a 50.4W prototype has been built and tested in the laboratory to verify the effectiveness of the electrolytic capacitor-less LED driver.