In contemporary times, the power consumption is very large. As a new light source with high efficiency, environmental protection, energy saving and earthquake resistance, LED has been more and more widely used in all aspects of national life. The vehicle LED lighting system with LED as the lighting source also appears more and more in rail vehicles. Based on the particularity of rail vehicles and the complexity of electrical system, it is particularly important to improve the reliability of LED lighting system in rail vehicles. Once the LED lighting system of rail vehicle compartment fails, it will not only cause the paralysis of one compartment lighting system and the whole vehicle lighting system, but also cause the failure of other associated systems, such as air conditioning system, operation control system, electrical system, etc., and may even lead to fire and cause unpredictable losses. Timely and accurately determine the fault of LED lighting system in rail vehicle compartment, and carry out fault diagnosis and prediction, which is of great significance to reduce the maintenance cost of rail vehicle compartment lighting system, improve operation efficiency and reliability, and ensure the safe operation of vehicles.

How to design an embedded LED car lighting system

In order to timely and accurately determine and eliminate the faults of LED lighting system in rail vehicle compartment, this paper makes a comprehensive overview of its common fault types, and analyzes its fault mechanism, which lays a foundation for fault diagnosis and prediction.

1 – composition and template division of LED lighting system for rail vehicle carriage

The LED lighting system of rail vehicle carriage takes the industrial computer as the control core and communicates with the lower computer through CAN bus. The illuminance sensor is used to collect the illuminance value of the external environment of the carriage, and the illuminance information is transmitted to the PC through the CAN bus. Then the PC controls the opening or closing of the switch according to the illuminance value of the external environment, and sends instructions to the single chip microcomputer to control the single chip microcomputer to send PWM signals with different pulse width to the LED driver, so as to adjust the output luminous flux of the LED lamp.

The rail vehicle compartment LED lighting system mainly includes the following four modules: LED control circuit module, LED driving power module, LED lamp board module and sensor acquisition module. The circuit of the whole lighting system is complex and there are many electronic components. In practical application, if any part of the circuit or any component fails and can not work normally, it may cause paralysis of local or even whole vehicle lighting system and affect normal driving safety.

Taking the rail vehicle compartment LED lighting system as a unit, starting from the failure form of each module itself, combined with the special operating conditions of rail vehicles, the fault mechanism of rail vehicle compartment LED lighting system is deeply analyzed.

Failure mechanism analysis of 2-led control circuit module

The LED control circuit module is the control core of the LED lighting system of the whole rail vehicle compartment. It is connected with the peripheral circuit, with IPC as the control core, can bus communication and led driving power module. In the LED control circuit module, in addition to IPC and can bus, it also contains many electronic components, such as single chip microcomputer. In order to lay a foundation for the fault diagnosis of LED control circuit, the fault mechanism of each component unit of LED control circuit module is analyzed.

2.1. IPC fault mechanism analysis

IPC is the brain of the whole rail vehicle compartment lighting system and controls the activities of each unit and module. If IPC fails, the whole rail vehicle compartment LED lighting system will not work normally. Generally, IPC faults of LED lighting system in rail vehicle compartment mainly include: connection fault, power supply fault, hardware fault and software fault. During the operation of rail vehicles, strong vibration causes hidden dangers to the connection problems of IPC. The fault causes mainly include patch cord problems, connecting wire faults and external equipment faults.

Power supply failure mainly refers to the peripheral power supply supplying IPC demand, which is the power supply problem of rail vehicles, which will not be discussed in detail in this paper; Hardware failure mainly refers to the problem of IPC hardware, such as CPU, ram and other hardware, which makes IPC unable to work normally; Software failure means that the software and program controlling the LED lighting system of rail vehicle compartment are abnormal. Generally, the troubleshooting steps for IPC are to check the connection first, then check each power supply, check the hardware condition, and finally check the software fault.

2.2. Circuit board fault mechanism analysis

Circuit board is the carrier of control circuit and an important part of circuit. The circuit board is mainly composed of analog circuit and digital circuit. The general digital circuit has only two states: 0 and 1. Because the state of digital circuit is less, it is less affected by noise, vibration, etc. Its working mechanism is mainly logic operation, there is no continuous mathematical function, and the test is relatively accurate. Therefore, the fault mechanism is relatively simple. The causes of analog circuit faults are complex, which are not only caused by the defects of components in the design and manufacturing process, but also caused by the aging of components or poor service environment caused by long service time. At the same time, the fault phenomena of analog circuits are diverse, and the component parameters are discrete and nonlinear.

Analog circuit faults can be divided into hard faults in which the circuit function cannot be realized due to some reasons (such as open circuit, short circuit, etc.) and soft faults in which the component parameters of the circuit drift and exceed the predetermined tolerance range due to some reasons. Among them, hard faults generally do not have slow variability. In the LED lighting system of rail vehicle carriage, there are more soft faults of analog circuit. The damage caused by soft fault to the system is gradual and difficult to identify. In the LED lighting system of rail vehicle compartment, the environment in which rail vehicles often live is characterized by high noise, strong vibration and bad environment. These noise and vibration are more likely to drift components and slow change faults.

There are many electronic components in the circuit board, so the resistance is selected as the research object. In order to facilitate the experiment, the fault waveform of the resistance with the same function in the circuit is analyzed when only one R0 fails. Waveform 2 in the figure shows that the waveform of LED lighting system will change when resistance R0 fails under normal working state. By comparing and analyzing the output waveform, it can be determined whether the resistance R0 is faulty.

2.3. Fault mechanism analysis of single chip microcomputer

Single chip microcomputer is the micro controller of LED lighting system in rail vehicle carriage, which plays the role of control core in many links. For example, the data collected by the illuminance sensor needs to be transmitted to the single chip microcomputer for processing. In the operation of rail vehicles, high temperature, low temperature and vibration will threaten the normal operation of single chip microcomputer. High ambient temperature or poor heat dissipation of the device will cause accelerated aging or damage of the single chip microcomputer, resulting in intermittent data errors, etc; If the ambient temperature is too low, the wiring between the chip and the pin may be broken. According to the fault mechanism analysis and general fault diagnosis methods of single chip microcomputer, the general steps of fault diagnosis of single chip microcomputer in rail vehicles can be summarized.

Failure mechanism analysis of 3-LED driving power module

In the LED driving power module, the main faults often appear in the circuit board or LED driving chip. The circuit board fault has been analyzed in detail in the previous section and will not be repeated here.

In the rail car, there are certain requirements for the luminous flux of the light, so the LED driver chip is an essential part of the control circuit. Chip overheating is the main cause of chip failure, and it is also the main problem restricting the development of LED at this stage.

The internal devices of the chip are short circuited, resulting in the increase of the power supply current of the chip; The chip with increased external power supply voltage increases the power supply voltage and current of the chip at the same time; Poor heat dissipation and heavy load work for a long time, resulting in hot chip; The load of the chip output port becomes heavier (the load impedance becomes smaller), resulting in the increase of the chip output power; The chip output port is short circuited, resulting in a sudden increase in chip output power; Some device parameters inside the chip change (such as device parameter time drift) or some internal devices are damaged, resulting in the change of chip working state and abnormal operation; The change of device parameters outside the chip (such as time drift of device parameters) or the damage of external devices lead to the change of chip working state and abnormal operation; When the chip works, the internal signal oscillation caused by self excitation directly leads to the abnormal output of the chip; When the chip is working, the duty cycle of the internal digital pulse signal changes due to various reasons, which directly leads to the abnormal output of the chip; An abnormal signal processing chip caused by electric pulse interference or interference wave coupled to the signal circuit of the chip; Abnormal operation of the chip caused by incorrect connection, short circuit and damage of external related devices and circuits; The filter failure of chip power supply circuit leads to excessive AC ripple and enters the chip power supply circuit; The AC power supply voltage is too high, resulting in an increase in the power supply voltage of the chip; The internal working disorder of some special chips caused by radio wave and electromagnetic interference is the cause of chip overheating.

Failure mechanism analysis of 4-LED lamp board module

LED light panel module is the terminal of LED lighting system for rail vehicle carriage. It is the core component of the system and a part of the control object of all services. If the LED light board fails, other links of the lighting system will lose their function. The faults of LED light board mainly include connection line fault and LED light source fault. The main reason for the failure of the connecting line is the open circuit of the line. The main causes of line breaking are wire aging and environmental factors. The traditional detection methods are manual testing with three-way meter and oscilloscope.

LED light source failure includes two types: power supply and drive failure; Led failure. The power supply and drive faults have been described in the fault mechanism analysis of LED power module. This section mainly analyzes the fault mechanism of LED lamp. The causes of LED lamp failure are mainly caused by super current, high voltage (such as lightning, instantaneous noise of circuit on and off, unstable power supply voltage, etc.) and electrostatic discharge. Among them, electrostatic discharge damage is a frequent fault in LED lighting.

Failure mechanism analysis of 5-led illuminance sensor acquisition module

Sensor is an indispensable core component of measurement and control system, and it is also the main tool to complete signal acquisition. In the LED lighting system of rail vehicle carriage, illuminance sensor is an important part of the system to realize illuminance adjustment. The core component of the illuminance sensor selected for the LED lighting system of the rail vehicle compartment is the photodiode. When there is no light, the resistance is infinite. When there is light, the resistance immediately decreases to hundreds of ohms. We use this characteristic to detect whether there is light and the size of light.

Sensors are relatively reliable electronic components, but in the special application environment of rail vehicles, there will be more failure forms than other use environments. Generally, the failure modes of illuminance sensor include: out of tolerance of dark current, open circuit fault, small insulation resistance between input and output, large reverse current of light emitting tube and failure of photoelectric transmission characteristics. Most of these fault forms are caused by the performance defects of the device itself.

In addition to these fault forms, in the LED lighting system of rail vehicle carriage, due to weather, vibration, sand and dust and other factors during train operation, it will cause dust pollution, corrosion, high temperature, shock crack and other faults to the sensor, so that the sensor can not work normally, and the collected environmental illumination is inaccurate, thus affecting the illumination adjustment of the carriage. Sensor pollution, corrosion and cracking will damage the device and make it unable to work normally. In the illuminance sensor, good heat dissipation is an important factor to ensure its normal operation.

During the operation of rail vehicles, the temperature of illuminance sensor chip increases due to the bad environment or the attenuation of its own performance. The temperature rise of illuminance sensor has a great impact on its acquisition accuracy. The increase of temperature affects the luminous flux of the illuminance sensor, resulting in the distortion of the data collected by the sensor. The results show that the luminous flux decreases by 0.55 LM when the temperature increases by 10 ℃. Therefore, controlling the temperature of illumination sensor chip is the premise to ensure normal operation.

6 – small high output lens surface mount LED “csl0901 / 0902 series”

Rohm (headquartered in Kyoto, Japan), a world-renowned semiconductor manufacturer, launched a small high output lens surface mount LED “csl0901 / 0902 series”. The new series product lineup includes 18 models of “csl0901 series” with ordinary brightness and “csl0902 series” with higher brightness.

In addition, this series also includes on-board products, which are suitable for the indicator light source of automobile odometer, with stable reliability that can be used in harsh environments. When miniaturizing the LED of automobile odometer, there is usually the problem of light leakage to adjacent parts. This series of products raise the position of light source from 0.18mm to 0.49mm of ordinary products, which effectively improves the problem of light leakage. Compared with the previous reflective led, the size (volume) is reduced to only about 1 / 18. In addition, all models adopt the structure that will not produce light decay in the high-temperature environment such as the interior of the car, and the products in blue and other colors adopt the newly developed molding resin.


Today, LED has become an indispensable part of our life. Not only automotive tail lights, but also digital display and indicator lights of display panels of various equipment in the field of automotive instruments, environmental lighting, industrial equipment, functional display in the field of consumer electronics, etc. LED has been widely used in various applications. It is expected that the demand for LED will further increase in the future.

The causes of LED lighting system failure in rail vehicle compartment are complex, so it is difficult to comprehensively analyze its mechanism. Based on the study of its working mechanism, the fault mechanism of LED lighting system in rail vehicle compartment is classified and analyzed, and the fault mechanism of control circuit, driving power supply, LED lamp board and sensor acquisition module in LED lighting system in rail vehicle compartment is deeply analyzed, which provides a reference basis for fault diagnosis of LED lighting system.

The engineer said, “in recent years, especially in the automotive and industrial equipment markets, the demand for ‘reliability’ has become higher and higher. Roma always takes “quality first” as the enterprise purpose and adopts a vertically integrated production system, which has played a great role in ensuring product reliability. In addition, refined service and technical support for customer needs are also crucial. In the future, Roma companies at home and abroad will strive to develop new products for applications that attach importance to LED added value such as reliability and design. “

Source: China Electronics Network

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