Infrared sensing PWM brightness control high brightness LED light production

I. Introduction

Design and manufacture an infrared brightness control HB-LED lamp. It can be used for panel lighting, corridors, work desk lamps, etc. The principle block diagram is as follows. Once inductive (such as waving), the brightness increases or decreases in turn. In order to meet the requirements, we stipulate (1) brightness of at least 3-5 levels (2) display with high brightness, power 0.5-2W.

Since the transmitting power of the infrared light emitting diode is small, the signal received by the infrared receiving diode is weak, so the receiving end is required to increase the high gain amplifying circuit. However, nowadays, whether it is amateur production or formal products, most of them use the integrated receiving head of the finished product. The infrared integrated receiving head is a module that integrates infrared receiving, amplifying, filtering and comparator output, and has stable and reliable performance. Therefore, with the integrated receiving head, people no longer make receiving and amplifying circuits, so that the infrared receiving circuit is not only simple but also greatly improved in reliability.

Second, the principle and design of each module

1. Infrared transmitting and receiving module

The characteristic of infrared is that it does not interfere with the work of other electrical equipment, nor does it affect the surrounding environment. The circuit debugging is simple. If the transmitting signal is encoded, multi-channel infrared remote control function can be realized. The infrared remote control system that people see is divided into two parts: transmitting and receiving. The emitting part of the emitting part is an infrared light emitting diode, which emits infrared light instead of visible light. The infrared wavelength of the commonly used infrared light emitting diode is about 940 nm, and the outer shape is the same as that of the ordinary φ5 mm light emitting diode, but the color is different. Generally there are three kinds of transparent, black and dark blue. Judging whether the infrared LED is good or bad is the same as judging ordinary diodes. This design uses TL0038BD integrated infrared receiver, which has low power consumption, high sensitivity and strong anti-interference ability, widely used in household appliances, remote control toys and other infrared remote control reception.

2.PWM control circuit

(1) Introduction to PWM technology

Pulse Width Modulation (PWM) is a very effective technique for controlling analog circuits by using the digital output of a microprocessor. It is widely used in many fields from measurement and communication to power control and conversion. In short, PWM is a method of digitally encoding analog signal levels. With the use of high-resolution counters, the duty cycle of a square wave is modulated to encode the level of a particular analog signal. The signal is still digital, because at any given time, the full-scale DC supply is either fully (ON) or completely OFF. The voltage or current source is either ON or OFF. The repetitive pulse sequence is added to the analog load. When the DC power is applied to the load, the power supply is disconnected when the power is turned off. As long as the bandwidth is sufficient, any analog value can be used. PWM is encoded. The wide application of PWM technology and its advantages are inseparable. One advantage of PWM is that the signal from the processor to the controlled system is digital, no need to perform digital-to-analog conversion. Keeping it in digital form minimizes the effects of noise. Enhancement of noise immunity is another advantage of PWM over analog control, and this is the main reason why PWM is used for communication at some point. From analog to PWM The communication distance can be greatly extended. At the receiving end, the modulated high-frequency square wave can be filtered out and restored to an analog form through an appropriate RC or LC network. The PWM control method also has various methods, including phase voltage control PWM, line. Voltage control PWM, current control PWM, and other methods.

(2) Implementation of PWM technology

In this experiment, the software generated method is used to control the PWM, and the 51 MCU generates an interrupt to generate the PWM modulation waveform, and controls the brightness of the LED by adjusting the duty cycle of the PWM. The C language implementation of the microcontroller is given in the appendix.

3. LED drive circuit implementation

The intrinsic characteristics of the LED determine that it is the most ideal light source to replace the traditional light source, and it has a wide range of uses. It has the advantages of small size, low power consumption, long service life, high brightness and low heat, sturdy and durable, and many changes.

According to the chip drive type, it is roughly divided into three types: constant current source, charge pump and switching power supply. According to the load connection method, it is divided into series type, parallel type and serial-parallel type. There are many professional driver chips on the market that integrate some LED driver circuits to solve the problem of converting high-voltage AC power into low-voltage AC (AC/AC), and then converting low-voltage AC power into low-voltage DC (AC/ DC), and then through the high efficiency DC / DC switching regulator step down and transform into a constant current source, output a constant current to drive the LED light source and other more complex problems. It is convenient to use and can easily and simply achieve the driving effect of high-power LED.

Thanks to the MAX5035 and MAX5033 chips that have been tried at MAXIM, there is a good solution for solving LED drivers. Based on a fixed frequency, high integration PWM switching converter MAX5035 output current up to 1A, MAX5033 output current up to 500mA, can fully meet the requirements of high power LED driver.

The circuit of this design is mainly divided into LED drive module, power supply module, single-chip module, feedback module, etc. After the final field test, the PWM interrupt program is continuously adjusted, and the pulse level signal can be generated by wavering. The brightness changes by 8 levels, the brightness is distinct, and the voltage amplitude is very stable, which better meets the design requirements.