At present, lighting is an important aspect of China's energy consumption. The annual electricity consumption for lighting is about 300 billion kWh, accounting for about 12% of the total power generation. With the economic development, China's lighting power consumption will increase by a large proportion; With the increasingly serious energy crisis and environmental protection issues, China's lighting industry must also take the green energy-saving development path. LED is a kind of semiconductor light-emitting device that converts electrical energy into light energy. It belongs to solid-state light source. As a new type of green lighting, its application prospects are attracting attention. Especially the development of high-brightness white LEDs makes LEDs in the field of lighting. The promotion and application will inevitably lead to a new revolution in the field of lighting.

Compared with current lighting devices such as incandescent lamps and fluorescent lamps, white LEDs have low heat generation, low power consumption (1/8 of incandescent lamps, 1/2 of fluorescent lamps), and long life (tens of thousands of hours or more, 10 times that of fluorescent lamps) ), small size, no pollution, fast response, safe and reliable, etc., is a potential product that is favored by the industry to replace traditional lighting equipment in the future.

At the same time, considering that some lighting products lack brightness adjustment, infrared remote control and other functions, they cannot meet the actual needs of modern lighting. Therefore, this paper designs an infrared remote control high-power white LED lighting system based on AT89S51 single-chip microcomputer. It adopts PT4115 high-power LED constant current driving scheme and infrared remote control technology, through a button encoding based on TC9012 infrared remote controller. Identification and decoding processing, multi-level PWM dimming function for LED light source can be realized by infrared remote control. This design provides great convenience for practical lighting applications while achieving high efficiency and energy saving.

1. System structure and function The lighting system adopts AT89S51 single-chip microcomputer as the main control chip, and selects 3 3W high-power white LEDs as the light source, adopts PT4115 chip to realize LED constant current drive system, and infrared remote control system is controlled by TC9012 remote control transmitter and HS0038 infrared. The receiver is constructed. The system block diagram is shown in Figure 1.

This system uses a home remote control using TC9012 chip as the infrared emission unit. It is widely used, low in price, and has many transmission codes. It can control the multi-level adjustment of the brightness of the LED light source. The infrared receiver is composed of HS0038, which is The integrated component with integrated infrared receiving head, amplification, demodulation and shaping circuit can output the TTL signal recognized by the single chip microcomputer; the infrared remote control information processing is realized by the single chip AT89S51, which mainly completes the identification of the infrared code sent by the remote controller. Decoding, and then generating a PWM dimming signal corresponding to the remote control key value according to the decoding result, thereby controlling the PT4115 constant current driving system to realize LED multi-level dimming function.

2, system principle

2.1 PWM dimming principle From the LED volt-ampere characteristics and mathematical model, it can be seen that the small change of the forward voltage of the LED after the forward conduction will cause large fluctuation of the LED current, and the ambient temperature, LED aging and other factors will also affect the LED. Electrical characteristics, if the LED current is out of control, long-term operation of the LED at high current will seriously affect its reliability and service life. The light output of the LED is directly related to the LED current, so the LED drive circuit should adopt the constant current drive mode when the input voltage and the ambient temperature change.

In practical applications, LEDs generally use two methods to adjust the brightness, namely analog dimming or PWM dimming. The analog dimming and PWM dimming comparison is shown in Figure 2. Analog dimming is to adjust the light efficiency by changing the current flowing through the LED. In addition to the change in brightness, it also affects the light quality of the LED. That is, the current change will inevitably lead to the chromaticity deviation of the LED.

The basic principle of PWM is to keep the LED forward current constant, and by adjusting the ratio of the time the current is turned on and off, the brightness adjustment from 0 to 100% can be achieved. The advantage of PWM dimming is that the current of the LED forward conduction is always constant, and the chromaticity of the LED does not change like analog dimming; while precisely controlling the brightness of the LED, it also ensures the chromaticity of the LED illumination.