The advantages of small LED size, low energy consumption, long life, environmental protection, and low heat have led to its rapid development and its wide application in various fields. Among them, long life is a very important advantage of LED. To ensure this advantage of LEDs, developers must ensure good EMC and reliability of LED systems. This article analyzes how to detect the EMC and reliability of LED systems based on an example.
1. Power system compatibility
Providing electrical power to LEDs or LED arrays is an important issue that must be considered when designing and implementing LED lighting devices and systems, as well as ensuring reliable end-user operation and compatibility with power supply systems. The power system includes various electrical infrastructure and utility grid utilities in people's daily lives.
Studies have shown that under normal circumstances, there are usually unreasonable wiring or grounding errors in power supplies that users have and operate. When general external power supply facilities are subject to general current interference, unreasonable or even incorrect wiring or grounding treatment will increase the degree of interference, increase the probability of damage to the user's electronic lighting device, and cause permanent damage to the device in severe cases. LED lighting devices and systems must have the ability to function properly in everyday electrical environments. Typical daily electrical environments include indoor and outdoor lighting, lighting inside and outside buildings such as shopping malls and factories, and LED street lights and searchlights on municipal poles.
2. Reliability of LED lighting devices and systems
First of all, what is reliability? It is defined as the ability of the product to perform the specified function within the specified conditions and within the specified time. With the development of science and technology, the design of modern operating machines, engineering equipment, vehicles and various types of exploration instruments is becoming more and more complex, and the functions are becoming more and more perfect. Therefore, the performance of these electronic and electrical products is becoming more and more serious. obvious. At the same time, the reliability of these machines and equipment has gradually received widespread attention, and this reliability is called system reliability. The reliability requirement is higher as the system becomes more complex. If the reliability does not meet the requirements of the system index, the greater the possibility of system failure, the greater the loss. These losses include economic, credibility, and even catastrophic consequences of life safety or more serious. For example, if the brake system of the car is unreliable or the work is wrong, the brake may be malfunctioning, which may cause significant loss or even danger to life. In the case of a major voting election, if the computer system is used, if the system fails, the statistical result will be disrupted. The consequences will be unimaginable. Therefore, it can be said that the introduction of the concept of system reliability has great significance for electronic products.
To improve the reliability of the system, on the one hand, it is necessary to improve the reliability of each component that constitutes the system. For example, to improve the reliability of the vehicle brake, firstly, the reliability of the brake position and control system should be improved. On the other hand, it is necessary to improve the reliability of the system against misoperation.
The root of improving system reliability lies in the design of the system. In order to make the components of the system work under normal conditions, there is no phenomenon such as overload and overload, and there must be a certain margin. It is also possible to design an alternative solution that will allow the system to function even if individual components or equipment fail. Of course, the design of the alternative solution may increase the complexity and cost of the system, but if the design is reasonable, it is worthwhile to have a good cost performance in terms of cost increase and system reliability improvement.
3. LED lighting device and system compatibility
The compatibility problem of electronic products is mainly electromagnetic compatibility (EMC), which is defined as the coexistence state of devices, systems, and subsystems that can perform their respective functions together in a common electromagnetic environment. That is, the device, system, and subsystem are not subject to the electromagnetic emission caused by other devices in the same electromagnetic environment, or suffer from impermissible performance degradation, and will not cause other devices, systems, and subsystems in the same electromagnetic environment to be electromagnetic. The launch causes or suffers from impermissible performance degradation. Electromagnetic compatibility includes two aspects: electromagnetic interference (EMI) and electromagnetic resistance (EMS).
The former mainly manifests as conducted interference and radiated interference. Conducted interference mainly causes interference signals generated by electronic equipment to generate interference through conductive medium or common power line. Radiation interference means that interference signals generated by electronic equipment transmit interference signals to each other through spatial coupling. Network or electronic device. The latter mainly refers to the system's resistance to interference such as electrostatic discharge, radiation, pulse group, lightning strike, conduction, etc., that is, anti-interference ability. Electronic products are generally classified into civilian-grade, industrial-grade, and military-grade products. Products of different grades have different standards. Products that meet these standards at a specific level are called electromagnetic compatibility. How to judge whether the product is electromagnetically compatible? This needs to be done through a series of compatibility tests.
4. Electromagnetic compatibility test
As mentioned above, the electromagnetic compatibility test of the system can be divided into electromagnetic interference (EMI) and electromagnetic resistance (EMS). Several important steps when using LED lighting devices and systems are as follows:
1) Conducted interference
Conducted interference refers to the electromagnetic interference generated by the LED lighting device itself to conduct conductor transmission. This test frequency range is generally 9KHz ~ 30MHz, which is a low frequency phenomenon.
2) Radiated interference
Radiated interference is also an interfering electromagnetic wave generated by the device itself and formed by spatial propagation. The LED lighting device is externally radiated by the internal circuit through the wire or structural housing of the product, which is equivalent to the antenna emission effect.
3) Harmonic current interference
One of the causes of harmonic currents is the non-linear load. Harmonic current interference will affect the waveform of the supply current and cause it to be distorted. This interference will cause pollution to the power grid and must be controlled.
4) Electrostatic discharge anti-interference ability
The human body is electrostatically charged. This phenomenon is more serious in the dry winter. The friction in this environment can easily cause the human body to carry a large amount of static electricity. At this time, if the human body touches the LED product or its adjacent equipment, it will form direct or indirect. Discharge, the generated pulse voltage may cause breakdown of the LED, so there is a very high requirement for the antistatic ability of the LED product.
5) Resistance to fast transient burst interference
The product's relay opening and closing or switching on and off will also cause interference to other electronic devices in the same circuit, with the characteristics of pulse grouping, high pulse repetition frequency and short rise time of pulse waveform.
6) Lightning surge immunity
Lightning strikes create a high energy surge voltage and current on the cable, which can easily cause damage to the device. In addition, large switch switching moments also create surge voltages and currents on the power supply line.
7) Cycle drop anti-interference ability
Voltage dips, short interruptions, and voltage changes are collectively referred to as cycle drops. The resistance index of the Zhou Bo drop interference evaluates whether the LED lighting device has the ability to work in an unstable power grid.
In the above test steps, the first three items are EMI indicators, and the last four items are EMS indicators. It is worth noting that for self-rectifying LED lighting products, only the input end is required to test, rather than self-rectifying LED lighting products, it is necessary to test the input and output of the matching drive control circuit and the input of the LED product separately. end.
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