LED street light brightness control design

At present, in the field of high-brightness LED street lamp drivers, there are two main technical solutions that are widely used at home and abroad: "using dedicated power chips" and "switching power supplies using discrete components", and for the purpose of "intelligent", Usually, the MCU is added as the main control chip of the system management on the basis of these two schemes. Therefore, the two solutions can be reduced to the "traditional multi-chip technology solution" of "system management + power control", and there are many chips and hardware. The disadvantage of the complicated structure, especially when it is required to drive multiple high-brightness LED strings in an LED street lamp driver, this disadvantage is particularly prominent.

Principle introduction

The new Piccolo TMS320F2802x/3x MCUs feature the latest architectural advancements and enhanced peripherals with a minimum package size of 38 pins, enabling 32-bit real-time control in low-cost applications. Real-time control enables higher system efficiency and precision by implementing advanced algorithms in industrial, consumer, and automotive applications such as solar micro-inverters, LED lighting, large home appliances, and hybrid vehicle batteries.

The Buck type switching power supply is one of the widely used power supply solutions. By selecting the appropriate output inductor and switching frequency, the system can operate in the continuous mode of inductor current; the LED Lighting Demo based on TMS320F28027 is based on the Buck type switching power supply. Principle, make full use of TMS320F28027 on-chip PWM (up to 8 PWM outputs) and ADC (up to 16-channel ADC) and other peripheral resources and combined with the corresponding control algorithm to achieve current closed-loop control.

As shown in the figure, the system includes seven modules: main control chip TMS320F28027, drive circuit, switching component, feedback network, off-chip memory for storing system configuration information, data acquisition interface and system expansion interface. After the power-on reset of the main control chip, the set values of the LED brightness, the on-off period, the on-off mode and the like are loaded from the off-chip memory as control parameters, and the control parameters and the feedback amount (including the grid collected by the data acquisition interface) are adopted. The algorithm of voltage, ambient brightness, system temperature and other parameters is processed to obtain the frequency and duty ratio of the PWM signal, and then the PWM signal is output. After the PWM signal is amplified by the driving circuit, it is used to drive the switching element in the switching power supply, so that the system is The high-brightness LED street light is supplied with power, and the voltage level 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 correct the control effect. The extended interface provided by the system is used for data interaction with other peripheral modules to facilitate the expansion of the functions of the drive in practical applications, such as mounting a Zigbee or GPRS module through an expansion interface to implement network management of the drive and Remote maintenance.

Program characteristics

The TMS320F28027-based high-brightness LED driver single-chip solution combines system management and power control into one, reducing the complexity of hardware design, while taking into account the flexibility of the design of the drive output number, by changing the periphery of the control chip The contents of the memory enable customization of control parameters such as LED current size, lighting period, lighting mode, ambient brightness and system temperature, and network management and remote maintenance of the system through the data interface of the MCU. The TMS320F28027-based high-brightness LED driver single-chip solution has the following features:

Low cost - single chip solves multi-channel constant current control, eliminating dedicated constant current chips, effectively reducing system cost

High efficiency - non-isolated switching power supply, no transformer leakage loss, high conversion efficiency, overall efficiency up to 95% when the system is fully loaded

Strong driving ability - 8-channel non-isolated constant current drive output, can drive 8 strings (no less than 14 per string) LED, the total output power is not less than 100W

Flexible control - using high-performance DSC as the control core, the advantages of 32-bit real-time control function can be fully utilized, and the current size and brightness of each LED can be independently controlled.

Good scalability - reserve 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, extended GPRS module for LED street lights, etc.)

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

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