The electromagnetic compatibility of the power adapter

　　The basic concept of 5V1A power adapter electromagnetic compatibility!According to the definition given in the national standard GB/T4365-2003 "Electromagnetic Compatibility in Electrotechnical Terms", electromagnetic compatibility (EMC) means that the equipment or system can work normally in its electromagnetic environment and does not constitute an unbearable electromagnetic Ability to harass.

　　Interpreting this definition, it can be found that the electromagnetic compatibility of a device includes two aspects. One is that it can work normally in an electromagnetic environment, so it needs to have sufficient resistance to electromagnetic disturbance in the environment. This is called the sensitivity of the device. Susceptibility; on the other hand, the electromagnetic disturbance generated by the device should not be too strong, so as not to cause interference to other devices in the same environment, which is called the electromagnetic emission of the device (Emission). Combining the above two aspects, a device with good electromagnetic compatibility should have low enough electromagnetic sensitivity and low enough emission intensity.

　　Therefore, in the electromagnetic compatibility standard system, some standards stipulate that under certain test conditions, various electrical and electronic equipment should be able to withstand the intensity of electromagnetic disturbance, thereby limiting their electromagnetic sensitivity, and other standards also stipulate The strength of electromagnetic disturbance signals allowed by various electrical and electronic equipment to be emitted.

　　The two terms that need to be mentioned here are "electromagnetic disturbance" and "electromagnetic interference". From the standard, it can be known that electromagnetic disturbance refers to "may cause the performance of devices, equipment or systems to be reduced or cause damage to animate or inanimate substances." Electromagnetic phenomena of harmful effects", and electromagnetic interference refers to "degradation of the performance of equipment, transmission channels or systems caused by electromagnetic disturbance." Therefore, electromagnetic disturbance refers to the electromagnetic signal itself that causes the interference, and electromagnetic interference refers to the result.

　　The camera power adapter needs three elements to form electromagnetic interference, one of which is indispensable, as shown in the figure.

　　The electromagnetic compatibility design is to start from these three aspects, either to reduce the intensity of the harassment source, or to reduce the sensitivity of the interfered object, and it can also block the transmission path to eliminate the interference phenomenon.

　　The electromagnetic compatibility design of electrical and electronic devices mainly focuses on improving the anti-interference ability (reducing electromagnetic sensitivity) and reducing electromagnetic emission, but the degree is different. Some equipment produces strong interference, but it is not easy to cause external interference. While affecting normal work, some have almost no interference, but are particularly susceptible to interference and abnormalities. The power adapter belongs to the former in general. Therefore, in the EMC design of the European power adapter, the most important work is to take a variety of measures and measures to reduce its emission intensity to meet the limit requirements of the relevant standards.

　　On the other hand, under strong external interference conditions, the control, protection and drive circuits of the power adapter may also deviate from the normal operating point, malfunction or even abnormal damage, so the anti-interference performance is also in the design Issues to consider.

　　The charger manufacturer will first introduce the EMI model of the power adapter, and give the design method of the EMI filter based on this, and finally introduce the anti-interference design with a small amount of space.

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