为构建照明用LED的PWM调光电路,设计了以上位机控制C8051F021微控制器为核心器件的1 kHz频率PWM信号发生器和以555定时器为核心器件的手动调节PWM信号发生器。阐述了这两种模式的PWM信号产生电路相互切换的方法,考虑了PWM信号的逻辑电平变换及其驱动缓冲、通讯接口隔离等实际设计要求。结果表明在微控制器运行模式下产生的PWM信号频率误差小于4‰,占空比误差小于0.1‰。本电路目前已应用于输入额定电功率达450 W、含有9个LED串列的某特种照明装置中。

In order to construct PWM dimming circuit for LED illumination, upper-computer controlled PWM generator based on C8051F MCU as a kernel device and manual controlled PWM generator based on 555-timer as a kernel device are designed. Method for switching these two kinds of running mode to each other is illustrated. In addition, demands for logic levels shifting and their driving abilities, as well as serial communication interface and its isolation are taken into consideration. In the MCU running mode, frequency error of PWM dimming signal is less than 4‰, and duty ratio error of the signal is less than 0.1‰. This circuit has been applied to a type of special lighting equipment, which includes 9 LED strings with rated power of 450 W.