EOS (Electrical Overstress) is a disruptive power surge with microsecond duration (typically the electrostatic discharge lasts for tens of nanoseconds). The surge simulator for IEC 61000-4-5 standard is used to simulate the lightning coupled to the grounding system of electronic installation, as well as the sudden surges caused by overvoltage during insertion or removal of power switch.
When designing a product, it usually classifies the product according to environmental conditions that such product to be used by consumer. TVs, computers and home appliances are normally considered as indoor electronic devices that are specifically designed to protect against electrostatic discharge due to frequent human operation. As for the other type of products classified to outdoor electronic devices, the addition of EOS protection is required while taking into account the possibility of lightning strike. However, currently some brand manufacturers of indoor electronic devices also expect to install EOS protection in their products. Why?
One of the reasons is the consumer usage habits in different regions. For example, a TV manufacturer sells the TVs to worldwide, but has higher return rate in South America and Southeast Asia, and the repair reports exhibit EOS damage. After sending investigators to these two regions, the manufacturer finally understands that the local consumers are used to placing their indoor TVs outdoors to enjoy with neighbors. The external environment factors cause interference issues and damage to TVs. There is another situation in developing countries: the TV manufacturer had been receiving customer claims about the connection failed between TV to set-top-box (STB). It was thought to be CDE (cable discharge event) issues, similar to the electrostatic discharge (ESD) events. However, the repair reports showed large burned areas caused by EOS. After the investigation, it was found that the two-prong outlets for TV power supply were not grounded. If the earth ground of two devices does not have the same reference level, it is easy to generate electric pressure surges, or even create a spark, when one unit is connected to another.
In some cases, EOS damage still occurs when the display monitor is placed inside the building and the connected devices are grounded as well. What causes it to happen?
Here we have an example of surveillance systems: the outdoor camera uses the LAN Port (RJ45) to connect to the indoor NVR. Since the wiring of the LAN Port may be run outdoors, all surveillance system manufacturers already provide a complete EOS solution for such conditions (the complete LAN Port protection solution offered by Amazing Microelectronic Corp. is shown in the figure below). However, if the energy produced by lightning strike cannot be quickly released after entering the system from the LAN Port, it may be transferred to the display monitor of the surveillance system through an audio-video port (such as HDMI) resulting in damage. Therefore, for this type of system that is partially placed in outdoor space, replacing the protection component of the display connection port (HDMI is shown in the figure below as example) with EOS control materials can effectively improve the interference tolerance of audio-video port.
The technology and design associated with ESD have been developed for several years. Engineers are now quite familiar with ESD protection. However, EOS is still a potential hazard that is easier to be ignored relatively. It may not happen regularly in our daily life, but frequently occurs in other applications or regions. A damaged product will affect consumer experience and impact the reputation of the brand. Therefore, it is necessary to determine the protection measures professionally and apply the specific antidote. By adding the component of TVS diode, it can greatly improve the EOS specifications, reduce the return rate, protect product value and optimize user experience to achieve a win-win outcome.