LED Lighting Energy-saving Street Light Design Solution

High-power, high-brightness power LED is a green and environmentally friendly light source with high efficiency, energy saving and long luminous life. It is driven by adjusting the current flowing through the LED, so the brightness control of LED street lamps is generally achieved by controlling the output current of the LED driving circuit. At present, in the field of high-brightness LED street lamp drivers, the two main technical solutions widely used at home and abroad are "using dedicated power supply chips" and "using switching power supplies with discrete components". In order to meet the needs of "intelligence", a single-chip microcomputer is usually added as the main control chip for system management on the basis of these two solutions. Therefore, these two solutions can be attributed to the "traditional multi-chip technical solution" of "system management + power control", which has the disadvantages of using many chips and complex hardware structure, especially when it is necessary to drive multiple high-brightness LED strings in one LED street lamp driver. This disadvantage is particularly prominent.

Principle Introduction

The new Piccolo TMS320F2802x/3x MCUs use the latest architectural technology and enhanced peripherals, with a minimum package size of 38 pins, bringing the advantages of 32-bit real-time control functions to low-cost applications. Real-time control can achieve higher system efficiency and accuracy by implementing advanced algorithms in industrial, consumer and automotive applications such as solar micro-inverters, LED lighting, white goods and hybrid vehicle batteries.
Buck switching power supply is one of the most widely used power supply solutions. By selecting the appropriate output inductor and switching frequency, the system can be operated in the continuous inductor current mode; the LED Lighting Demo based on TMS320F28027 is based on the principle of Buck switching power supply, making full use of TMS320F28027 on-chip PWM (up to 8 PWM outputs) and ADC (up to 16-channel ADC) and other peripheral resources and combining with the corresponding control algorithm to achieve closed-loop current control.

As shown in the figure, the system includes seven modules, including the main control chip TMS320F28027, the drive circuit, the switch element, the feedback network, the off-chip memory for storing the system configuration information, the data acquisition interface and the system expansion interface. After the main control chip is powered on and reset, the set values ​​of the parameters such as LED brightness, on/off period, on/off mode, etc. are loaded from the off-chip memory as control parameters. Through the algorithm processing of these control parameters and feedback quantities (including the grid voltage, ambient brightness, system temperature and other parameters collected by the data acquisition interface), the frequency and duty cycle of the PWM signal are obtained, and then the PWM signal is output. After the PWM signal is amplified by the drive circuit, it is used to drive the switch element in the switching power supply, so that the system can supply power to the high-brightness LED street lamp, and the voltage at both ends of the LED street lamp and the current flowing through the LED street lamp are fed back to the main control chip through the feedback network to realize the correction of the control effect. The expansion interface provided by the system is used to exchange data with other peripheral modules to facilitate the expansion of the driver's functions in practical applications, such as mounting Zigbee or GPRS modules through the expansion interface to realize the networking management and remote maintenance of the driver.

Solution Features

The high-brightness LED driver single-chip solution based on TMS320F28027 combines system management and power control into one, reducing the complexity of hardware design while taking into account the flexibility of the driver output path design. By changing the content of the memory outside the control chip, the control parameters such as LED current, on and off time period, on and off mode, ambient brightness and system temperature can be customized. The system can also be networked and remotely maintained through the MCU data interface. The high-brightness LED driver single-chip solution based on TMS320F28027 has the following characteristics:

Low cost - a single chip solves multi-channel constant current control, eliminating the need for dedicated constant current chips, effectively reducing system costs
High efficiency - non-isolated switching power supply, no transformer leakage loss, high conversion efficiency, the overall efficiency is as high as 95% when the system is fully loaded
Strong driving ability - 8 non-isolated constant current drive outputs, can drive 8 strings (each string is not less than 14) LEDs, the total output power is not less than 100W
Flexible control - using high-performance DSC as the control core, can give full play to the advantages of 32-bit real-time control function, each LED current size, on and off mode, etc. can be independently controlled
Good scalability - reserved temperature, brightness, color temperature and other detection interfaces, support serial port, I2C and other data interfaces, paving the way for system integration (such as Zigbee networking of LED street lights, expansion of GPRS modules, etc.)

In addition, the solution supports 12-bit ADC resolution and 256-step grayscale control; wide voltage input range, when using an additional system power supply, the input voltage can be as high as 100V; when the control system and LED string share a DC power supply, up to 60V; supports undervoltage lockout and overvoltage protection, supports over-temperature protection extension, no-load detection, over-current protection, automatic brightness power-off storage, and four-channel group delay noise reduction.