Regarding the interference problem of EFT, it is mainly divided into two parts: practical application and certification test. In practical applications, it may be encountered that when the high-power motor or the electric switch is operated, it will affect the normal operation of the control circuit, and we need to rectify it to meet the functional requirements. In some compulsory certification products, relevant test standards need to be passed, and the specific standards vary depending on the product type.
Figure 1 EFT test
The primary purpose of the EFT test is to verify the immunity of electrical and electronic equipment to various types of transient disturbances, such as from switching transients, such as switching off inductive loads, bounces of relay contacts, and the like. In the circuit hardware design, we need to consider the two transmission paths of EFT, namely conducted interference and radiated interference. Since EFT interference is a common mode type interference, a large part of the interference will appear as spatial radiation interference.
Case device failure
The main function of the product is to control the start and stop of the high-power motor and monitor the running status of the motor. Most of the motors are inductive loads. When the motor starts and stops, it will generate spike interference pulses in the power supply grid. This interference is easily disturbed by the power supply line and space radiation to the powered devices. Generally, the program control is abnormal and the device is restarted. And so on.
Specific phenomenon: When the motor starts, the control unit will restart, causing the entire system to fail to operate normally.
First, the program problem has been eliminated. The next step is to confirm the problem point and disconnect the motor part from the separate operation control part. The abnormal phenomenon disappears.
Failure phenomenon analysis and rectification
First, the program problem has been eliminated. The next step is to confirm the problem point and disconnect the motor part from the separate simulation running control part. The abnormal phenomenon disappears. The initial determination is due to the pulse spike caused by the motor start. Next, the interference path is mainly analyzed and rectified.
After viewing the power supply board, the following interference paths are analyzed and summarized, as shown in the following figure:
Figure 2 Analysis of interference path of power supply board
As can be seen from the above figure, the solution to the problem must proceed from these two aspects, as follows:
1. Coupling radiation interference path rectification: This type of interference is mainly to control the distance of the interference source or to isolate the interference source.
2. Reconstruction of conducted interference path: Conducted interference mainly interferes with the powered device through the wiring path of the power component. This part of the interference needs to be filtered on the conductive path.
According to the analysis of the original power board, the specific rectification measures are as follows:
Figure 3 Schematic diagram of power supply board rectification
After the rectification has solved the EFT interference problem, it proves that the analysis circuit interference path is correct. It is also worth noting that in addition to the peripheral circuit design, it is also important to choose a power module with superior EMC performance. At present, ZLG Zhiyuan Electronics has more than 12 years of R&D and application experience in power modules, which can provide you with more professional application support.
Figure 4 AC-DC power supply module
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