LED dimming system based on STC89C52 single-chip microcomputer circuit analysis

The arrangement of LED and LED light source, the requirement specification determines the basic drives. The main function of the LED driver is under the scope of certain working conditions limit, the current through the LED and no matter how to change the input and output voltage. The most commonly used is to use an electrical isolation transformer. Article discusses the dimming factors need to consider LED lighting design. Because of the requirements of the dimmer so drive LED faces many challenges, such as forward voltage changes with the change of temperature, current, and different individuals, different batch, different suppliers LED forward voltage difference also; In addition, the LED 'color' will be as the change of current and temperature and drift. Below with the method of multiple series, LED power supply for 12 v battery, so using the booster circuit. 1. System of LED dimming system composition block diagram as shown in figure 1. 1.

　　2. 2 unit of hardware circuit design. 1 based on MAX1771 booster ( 提高) Circuit MAX1771 is beauty, power management chip, can be used as a booster circuit, the circuit structure of the Boost circuit, the following figure 2. 1. When the voltage input voltage range is 5 - 12 v, output according to the adjusting range is 24 - 36V。 Pin 1 output PWM to control the field effect tube IRF3205 conduction and deadline. Pin 3 is a voltage feedback end, with 1. 25 v voltage source. When the input voltage is higher or lower than 1 to 3 feet. 25 v, the chip will automatically adjust the decrease or increase of PWM duty ratio, in order to get stable output.

  　　2. 2 LED drive circuit design of the LED drive circuit principle diagram as shown in figure 2. 2. The Buck driver circuit is more complex, therefore, use the following circuit, make present effect tube pass break the LED the cathode voltage rise, LED to shut down. Effect on the tube conduction, LED anode voltage was lower, LED light. PWM control method makes the driving circuit is more simple and reduces the manufacturing cost, and can obtain more accurate brightness step adjustment. Software design USES STC89C52 microcontroller PWM output frequency of 230 hz to drive the field effect tube IRF3205 open circuit, one with independent keyboard to realize PWM duty ratio 1% 99% continuous adjustable, step into the value of 1%. Use the LCD YJDC - at the same time 1 of the brightness of the LED the PWM duty cycle for display, formed a good man-machine interface. The software flow chart shown in figure 3. 1. Schematic circuit diagram and PCB diagram (1) single chip microcomputer and peripheral circuit principle diagram