Example analysis: How to detect EMC and reliability of LED systems

The advantages of LED, such as small size, low energy consumption, long life, environmental protection, and low heat, have led to its rapid development and wide application in various fields. Among them, long life is a very important advantage of LED. To ensure this advantage of LED, R&D personnel must ensure good EMC and reliability of LED system. This article analyzes how to detect EMC and reliability of LED system based on examples.

1. Compatibility of power supply system

Providing electrical power to LEDs or LED arrays is an important issue that must be considered from the design to the implementation of LED lighting devices and systems, as well as ensuring reliable working conditions for end users and good compatibility with the power supply system. The power supply system includes various electrical infrastructures and public facilities of the mains power grid in people's daily lives.

Research shows that, in general, the power equipment that users own and operate usually has various unreasonable wiring or grounding errors. When there is a general current interference in the external public power supply facilities, unreasonable or even wrong wiring or grounding will aggravate the interference, increase the probability of damage to the user's electronic lighting devices, and in severe cases, cause permanent damage to the devices. LED lighting devices and systems must have the ability to work normally in daily electrical environments. Typical daily electrical environments include indoor and outdoor lighting, lighting facilities 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 a product to complete the specified functions under specified conditions and within a specified time. With the development of science and technology, the design of modern operating machines, engineering equipment, transportation vehicles and various exploration instruments has become more and more complex, and the functions have become more and more perfect. Therefore, the performance of these electronic and electrical products has become more and more 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 index requirements are 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 and the greater the loss caused. These losses include economic, reputational, and even life safety or more serious catastrophic consequences. For example, the unreliability or working errors of the braking system of a car can lead to brake failure, which is likely to cause major losses or even life-threatening; in major voting elections, if a computer system is used for statistics, if the system fails at this time and disrupts the statistical results, the consequences will be disastrous. Therefore, it can be said that the introduction of the concept of system reliability is of great significance to electronic products.

To improve the reliability of the system, on the one hand, we need to improve the reliability of each component that constitutes the system. For example, to improve the reliability of automobile braking, we must first improve the reliability of the brake position and control system. On the other hand, we must also improve the reliability of the system in withstanding misoperation.

The root of improving the reliability of the system lies in the design of the system. The components of the system should work in a normal state, without overload or overload, and with a certain margin. You can also design a backup plan so that the system can still work normally even if some components or equipment fail. Of course, the design of the backup plan may increase the complexity and cost of the system, but if it is designed reasonably, it has a good cost-effectiveness in terms of cost increase and improved system reliability, and it is completely worth it. 3. Compatibility of LED lighting devices and systems

The compatibility problem of electronic products is mainly electromagnetic compatibility (EMC), which is defined as the coexistence state in which devices, systems, and subsystems can perform their respective functions together in a common electromagnetic environment. That is, the device, system, and subsystem will not be subject to or suffer unacceptable performance degradation due to electromagnetic emissions from other devices in the same electromagnetic environment, nor will it cause or suffer unacceptable performance degradation due to its electromagnetic emissions from other devices, systems, and subsystems in the same electromagnetic environment. Electromagnetic compatibility includes two aspects: electromagnetic interference (EMI) and electromagnetic tolerance (EMS). The former is mainly manifested as conducted interference and radiated interference. Conducted interference is mainly the interference signals generated by electronic equipment that interfere with each other through conductive media or public power lines; radiated interference refers to the interference signals generated by electronic equipment that are transmitted to electrical networks or electronic equipment through spatial coupling. The latter mainly refers to the system's tolerance to interference such as electrostatic discharge, radiation, pulse groups, lightning strikes, conduction, etc., that is, anti-interference ability. Electronic products are generally divided into civilian, industrial, and military products. Different grades of products have different standard regulations. Products that meet these standards at specific levels are called electromagnetic compatibility. How to judge whether a product has electromagnetic compatibility? This requires a series of compatibility tests.

4. Electromagnetic compatibility test

As mentioned above, the electromagnetic compatibility test of the system can be divided into two aspects: electromagnetic interference (EMI) and electromagnetic tolerance (EMS). The important steps when applied to 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 and transmitted through the conductor. The test frequency range is generally 9KHz to 30MHz, which is a low-frequency phenomenon.

2) Radiated interference

Radiated interference is also generated by the device itself and forms interfering electromagnetic waves that propagate through space. LED lighting devices generate external radiated interference from the internal circuit through the product's wires and cables or structural parts casing, which is equivalent to the antenna emission effect.

3) Harmonic current interference

One of the reasons for the generation of harmonic current is nonlinear load. Harmonic current interference will affect the waveform of the power supply current and distort it. This interference will pollute the power grid and must be controlled.

4) Electrostatic discharge anti-interference ability

The human body carries static electricity, which is more serious in the dry winter. In this environment, friction 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, direct or indirect discharge will occur, and the generated pulse voltage may cause the LED to break down and be damaged. Therefore, there are very high requirements for the anti-static ability of LED products. 5) Resistance to fast transient pulse group interference

The opening and closing of the product's relay or the on and off of the switch will also interfere with other electronic devices in the same circuit, with characteristics such as pulses appearing in groups, high pulse repetition frequency and short rise time of the pulse waveform.

6) Lightning surge anti-interference capability

Lightning strikes can cause high-energy surge voltages and currents on cables, which can easily damage components. In addition, large switch switching can also cause surge voltages and currents on power supply lines.

7) Frequency drop and anti-interference ability

Voltage drops, short interruptions and voltage variations are collectively referred to as voltage drops. The voltage drop resistance index measures 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 needs to be tested during testing, while for non-self-rectifying LED lighting products, the input and output of the supporting drive control circuit and the input end of the LED product need to be tested separately.