大功率LED在线性及PWM调光下的电光转换效率及热分析

Radiant efficiency and thermal analysis of high-power LEDs at linear and PWM dimming modes

在相同输入电功率下,对大功率LED在线性及PWM两种调光模式下的光参数及电参数进行了测试。比较了LED在两种调光模式下的色温、光效及电光转换效率随输入功率的变化,得出在两种调光模式下,色温随平均输入电流的降低而降低,但线性调光模式下的色温漂移大于PWM调光模式下的色温漂移;光效及电光转换效率随平均输入电流的降低而升高,但在相同输入功率下,LED在PWM调光模式下的电光转换效率大于线性调光模式下的电光转换效率,且随平均输入电流的降低,线性调光模式下的电光转换效率的上升速度要快于PWM调光模式。利用T3STER热阻测试仪,建立LED的瞬态热阻抗模型。使用电子学热仿真分析方法对LED在两种调光模式下的电光转换效率随结温变化的规律进行了仿真分析。分析得出LED在PWM调光下的光电转换效率主要受结温温升的影响,而在线性调光下,电光转换效率除了受到结温温升的影响,还受到无效电流注入的影响。因此,LED在线性调光模式下电光转换效率的上升速度要快于PWM调光模式。

Optical and electrical parameters of high-power LED at linear and pulse width modulated （PWM） dimming modes are tested at the same input electric power. Comparing color temperatures,lurninous efficienies and radiant efficiencies at different input electric power levels,it is observed that at two dimming modes, the color temperature decreases with decreasing average input current, and it drifts greater at linear dimming mode than PWM dimming mode. In addition, the luminous effideney and radiant efficiency decrease with increasing average input mode than that at PWM dimming mode. Moreover, with decreasing average input current, the radiant efficiency curve goes faster at linear dimming mode than that at PWM dimming mode. The thermal transient tester is used to build LED transient thermal impedance model. The phenomenon that the radiant efficiency of LED varies with junction temperature at linear and PWM dimming modes is analyzed using the electric-thermal simulation method. It is concluded that at pWM dimming mode, a decrease of radiant efficiency is mainly affected by junction temperature. However,at linear dimming mode,a decrease of radiant efficiency is not only affected by junction tern perature,but also by invalid injection current.