Beauty instruments are increasingly popular among consumers due to their small size and portability, but their small size makes their ESD issues particularly prominent. This also makes designers feel a headache when designing.
1、 Description:
The customer's prototype is a beauty instrument that can detect the moisture and oiliness of the human skin. If there is a lack of moisture, the skin can be hydrated through the beauty instrument. According to the customer's requirements, apply ± 4KV contact discharge and ± 8KV air discharge to the prototype. During actual testing, it was found that a ± 4KV contact discharge was applied to the USB metal port of the prototype, causing the prototype to shut down, Bluetooth to drop, and then restart to restore its function. This does not comply with the IEC61000-4-2 Class B standard. During the voltage reduction test, it was found that a similar phenomenon occurred when ± 1KV static electricity was applied to the prototype.
2、 Rectification process:
According to the phenomenon of power failure, which is similar to the normal shutdown by pressing the button, the first consideration was to parallel the ASIM ESD (model: ESD5D150TA) to the ground on the button. During testing, it was found that the phenomenon did not improve significantly. Further analysis ruled out the interference of the buttons, as they were pressed once to shut down the machine and then pressed again to turn it on. So if ESD interferes with the buttons, the phenomenon should be turning on and off at once; However, the actual phenomenon is that the machine will not start up after shutting down, and confirming with the customer that resetting may also cause this phenomenon. Therefore, the machine's RESET is connected to the ground in parallel with ASIM ESD (model: ESD3V3D250TA) and ASIM magnetic beads (model: CVB1005C152T) are connected in series. When conducting further testing, the prototype can pass 2KV, but cannot pass 3KV. Then set an electrostatic ground to discharge most of the static electricity directly onto the horizontal coupling board when it flows through the USB metal port; And isolate the USB metal shell from the GND of the PCB using ASIM magnetic beads (model: CVB1608C252T), as shown in the following figure:
When conducting further testing, the prototype showed no abnormalities during ± 4KV contact discharge, which meets the standard of EIC610000-4-2.
3、 Rectification experience:
The ideas for this rectification are useful for "blocking", "preventing", and "dredging". The USB metal port is isolated with magnetic beads for blocking, the signal line is connected to the ground in parallel with ESD for prevention, and adding static electricity to the ground for drainage. The process of electrostatic discharge is accompanied by radiation noise and conduction noise, which includes the static magnetic field, electric field, and magnetic field generated by discharging static electricity.
Shenzhen Asim Technology Co., Ltd. is located in Shenzhen Yinxing High tech Industrial Park. It is a high-tech enterprise that integrates independent research and development, production, sales, EMC design, and EMC technical support of electronic protection components. The company's main products include TVS ESD, filters, magnetic beads, and other protective devices, which are widely used in fields such as communication, computer/server, security, military products, automotive electronics, home appliances, industrial control, and digital consumption.
