16-way constant current LED driver chip to realize guardrail light

LED guardrail lights use fluorescent tubes or LEDs as light sources and continuous guardrails as carriers to form an approximately linear guardrail light strip. This article mainly introduces a guardrail light solution based on a 16-channel constant current LED driver chip. The solution mainly consists of the following parts: (1) The main control circuit based on the STC11F02 microcontroller, whose main function is to generate SPI control signals; (2) The LED driver circuit based on the LN0134, whose main function is to use its 16-channel constant current to load the LED; (3) The power input voltage conversion circuit and the LED power supply circuit, which mainly complete the functions of circuit protection, chip power supply, and LED light power supply.

Introduction to main chip functions

LN0134 is a 16-way constant current LED driver chip developed by Nanlin Electronics. The chip has a built-in 16-bit CMOS shift register and output latch, which can convert the input serial data into a parallel output format, thereby controlling 16 output current sources, and providing a constant and consistent current of 3 to 45 mA at each output end to drive the LED without being affected by the load. The output current can be adjusted by adjusting the size of the external resistor, so as to easily control the brightness of the LED, and the average current of all LEDs can be adjusted by inputting a PWM signal at the enable end (OE). At the same time, it also supports the SPI communication protocol, making it easy for us to control the communication data, so it becomes one of the best ICs for driving LEDs.

The STC11F02 microcontroller has 2K FLASH program storage space and 256B SRAM storage area embedded inside; the chip has an advanced instruction set structure, is compatible with the common 8051 instruction set, has hardware multiplication and division instructions, and does not require a programmer or emulator, and can be upgraded remotely. This solution takes advantage of its high speed, low cost, and streamlined I/O port to simulate the SPI protocol to achieve communication control of other ICs.

Guardrail Light Design

1) Hardware circuit design and principle

The basic principle of this scheme is: the single chip microcomputer simulates the SPI protocol, sends data to the LN0134 driver chip, and the LN0134 internal hardware circuit realizes the serial input and parallel output of data, drives 16×3 LEDs, and then controls the changes of LED lights by changing the data to achieve different combinations of LED lights, such as: running lights, twinkling, jumping, breathing and other effects. The circuit of this scheme is completed in the hardware environment PADS. In order to save costs, the generated PCB files are also single-sided boards.

2) MCU control signal circuit

Figure 1 is a diagram of the MCU control circuit. The control signals generated by the main control chip are: (1) SPI control signals, including four ports: OE, SDIO, SCLK, and LE; (2) LED power enable signals, including two ports: CONTROL1 and CONTROL2.

MCU control circuit diagram

3) LN0134 application circuit

The LN0134 application circuit is shown in the figure. The LED driver chip receives the SPI signal sent by the microcontroller. Different SDIO data will get different data from OUT0 to OUT15, thereby driving the LED to produce different change effects. The LN0134 chip supports multi-chip cascading. Through the data port SDO end, it connects to the SDI port of the next chip, and so on. The design of the long-distance guardrail light solution only needs to cascade small units one by one. Setting the resistance value of R30 can change the output current value, thus eliminating the trouble of multi-channel current limiting.

LN0134 Application Circuit Diagram

4) Power supply circuit

The power supply circuit is shown in the figure. This circuit supports an input voltage of 12V to 15V, and the positive and negative poles can be prevented from being connected in reverse through the rectifier bridge. A 5V power supply voltage can be obtained through IC1, which provides power for the microcontroller and LN0134 chip; IC2~IC6 can complete the power supply of the LED light group, and the CONTROL1 and CONTROL2 ports provided by the microcontroller can control the power supply of POVER1 and POVER2 to be turned on and off.

Power supply circuit diagram

5) Software Design

Software design is the lifeline of the entire solution. It directly determines the operation quality and efficiency of the entire solution, and also reflects the functionality and reliability of the solution. The on-chip program of the STC11F02 chip is written in the software development environment Keil uVision2. The focus of the program is to simulate the SPI communication protocol. The timing waveform of the theoretical design is shown in the figure. The software code is implemented in C language. The SPI waveform simulated by the microcontroller observed by the oscilloscope is shown in Figure 5. Among them, Tek1 is SDI; TeK2 is CLK; TeK3 is LE; TeK4 is OE, which meets the design requirements.

SPI Timing Diagram

SPI Waveform

First, the SPI simulation program is modularized, mainly for the convenience of calling; in the whole process, the data in the buffer changes the most. When the data changes, the corresponding display effect will change; continuous data changes produce different lighting, which also shows the colorful and dazzling characteristics of the guardrail lights.

Conclusion

This guardrail light design is a 1-meter-long unit module. For longer guardrail distances, these small units need to be cascaded to improve the driving ability of the control signal. The 16-channel LN0134 chip is selected to increase the number of LED lights. According to the performance parameters of the chip, changing the power supply circuit can better expand the application circuit and drive more LED lights. The STC11F02 chip is selected to save costs and simplify the main control unit. The overall design of this solution follows the principles of reliability, simplicity, and practicality, providing reference and help for more guardrail effects.