The history of lighting has gone through four revolutions. The first revolution was the emergence of fire. The second revolution was Edison's invention of the world's first incandescent light bulb in 1879. However, incandescent light bulb is very inefficient, with less than 5% efficiency in converting electric energy into light energy. The third revolution was the introduction of fluorescent lighting in the 1940s, which increased its energy conversion efficiency to 25%. The fourth revolution began in the 1960s with light-emitting diodes, which were so inefficient and bright that they could only be used as indicator lights for meters. It was not until the end of the 20th century that LED lights surpassed fluorescent lamps in luminous efficiency, reaching up to 30%, which was regarded as the fourth revolution in the history of human lighting.

LED drive power supply market and the downstream industry, especially in the closely related to the development of high power LED street light, but with the improving of the various performance parameters of the LED, LED lighting market gradually rise, wide range of applications, especially in 2012, the industry attention from outdoor to indoor commercial lighting applications at the same time, domestic and foreign markets and customers for the LED drive power supply has a higher request, especially the efficiency of power supply, power factor, the life and precision of constant current, electromagnetic compatibility, etc.
Although there are many kinds of ac input LED constant-current driving power integrated circuits, the models are different, but many of its external circuits have common elements, which are basically the same. This paper selects the most representative ac input protection circuit, electromagnetic interference filter, input rectification filter and PFC diode, drain clamp protection circuit, high frequency transformer and secondary side output circuit, and elaborates the design principle and matters needing attention of each unit circuit in detail.