A High-Power-Factor Flicker-free Long Lifetime LED Driver Research

Owing to its high luminous efficiency, High Brightness Light Emitting Diode has many advantages, such as having long working life, good optics performance, and less environment pollution. As it was invented, it had a huge development and became a new generation of “green light source”. The properties of the whole LED lighting system almost depend on the properties of the driving circuit, and LED driving circuit became the key link of the application of LED. Base on the requirements of high power factor, long lifetime and no flash, this paper researches into LED driving circuit.In order to achieve the purpose of high power factor, this thesis uses flyback converter as the PFC stage. When driver power is powered by AC power, the output of PFC stage contains the AC current with twice the line frequency.The load voltage of LED is constant, so the LED current also contains the AC current with twice the line frequency that would cause strobe light. So we need some energy storage elements to balance the output powers, one of the energy storage is ways is using large capacity electrolytic capacitor,but the lifetime of electrolytic capacitor is short, that would reduce the lifetime of the whole LED driving circuit. Based on classic flyback converter, this thesis modifies the circuit topology and proposes an innovative LED driving circuit. The high-frequency transformer of the innovative LED driver power has two secondary windings, When instantaneous power is too big, it can store extra power to capacitor by additional secondary windings; when instantaneous power is too small, the capacitor would discharge electricity to secondary windings., It resolves driving circuit’s dependencies of electrolytic capacitor, and achieves the purpose of constant output current for LED.This paper gives a detailed introduction on operating principle of the innovative LED driver power. It also makes a detail theoretical analysis and calculation on each component, proposes a control circuit and gives a detailed introduction on it.Based on the theoretical analysis, this thesis designed a 18-W experimental prototype after choosing the actual device. It validates the theory by experiment and proves that the High-Power- Factor Flicker-free Long Lifetime LED Driver is feasible.