With the continuous innovation of electronic technology, smart homes have gradually entered thousands of households. Since the users of smart homes are the general public, and the environment used in the north and south is very different, ESD is an important factor for electronic engineers to consider when designing products.
The product of this experiment is a large brand of smart home, the customer found in the ESD test, if the air discharge of the electrostatic gun against the screen test, the screen is easy to appear screen phenomenon, but when the whole machine test, the product will not appear screen phenomenon.
Through the analysis of the experimental phenomenon, it is judged that the display screen itself has no anti-interference. VIEW ITS PCB LAYOUT DIAGRAM, AS SHOWN BELOW:
AS CAN BE SEEN FROM THE PCB LAYOUT, THE SIGNAL TRACES OF THE RECTIFICATION SCREEN ARE VERY LONG, AND THE SIGNAL LOOPS ARE RELATIVELY LARGE. If there is a sensitive signal in it, it is exposed to the transient magnetic field generated by the air discharge, and it is easy to generate induced electromotive force (i.e. di/dt).
Corrective measures: We connected the communication signal between its MCU and the motherboard MCU to the ground parallel ESD (model: ESD5D100TA), and then when the air discharge was carried out, it was found to be a little improved, but it could not meet the customer's requirements.
According to the experimental phenomenon, to deal with this interference by magnetic field, we generally use another EMI device --- magnetic beads. Many engineers would believe that magnetic beads are generally used to solve radiation. However, a large number of experiments have proved that magnetic beads play an important role in static electricity. So we connected the magnetic beads in series on the signal network RS (model: CVB1005C182T), and through analysis, there is a fixed metal sheet on the screen, the original design is not grounded, and it is connected to the GND of the PCB when rectifying, and the lap is better. As shown in the following figure:
When I went to test after rectification, I found that the air 15KV hit the screen, and the working state of the screen did not have any abnormalities. Test passed!
