700V Constant Current LED Lighting Controller

A light-emitting diode(LED) is a two-lead semiconductor light source. It is a pn-junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device,releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light(corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.The incandescent lamp and fluorescent lamp can be directly connected with ordinary 220 Vac,but LED must be driver with a suitable DC voltage.Therefore,the LED drivers have become the most important part of LED lighting industry.The LED drivers is faced with many challenges,such as electrolytic capacitor life,LED current accuracy,power conversion efficiency and EMI/EMC.The thesis firstly introduces the research background and the significance of the this work. Then it describes the development of the LED, and introduces the theory and characteristics of the different LED drivers.Afer the theoretical research of the LED dirvers, it introduces the design of a 700 V LED lighting constant current driver,including the design of start-up and automatic restart,the principle of ciruit,current detecting and leading edge blanking,controlling protection.The chip is a monolithic constant current LED lighting controller which adopts primary-side feedback in switch mode power supplies. It achieves constant current output in universal input voltage. The accuracy of constant current is less than ±5%.The controller method accurately controls the LED current from the primary side,therefore significantly simplifies the LED lighting system design by eliminating opto-coupler, TL431 and auxiliary winding. The circuit is designed for working in discontinuous conduction mode. The controller features cycle-by-cycle current limit,over-voltage protection and output short-circuit protection, in order to improves the system reliability and safety. The controller is available in SOP-8 Package.