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TVS tube? ESD? How to choose the best protection device in the circuit?

sohu | 28/06/2021

One. What components do circuit protection mainly support? What are the main functions of these components?

Circuit protection devices mainly include: overvoltage protection devices, overcurrent protection devices, and overtemperature protection devices.

Overvoltage protection: This type of device is mainly used to protect subsequent circuits from load dumping or instantaneous high voltage damage. Commonly used overvoltage protection devices include semiconductor discharge tubes, TVS transient suppression diodes, ESD static suppressors, solid discharge tubes, Ceramic gas discharge tube and varistor, etc.

Over-current protection: Over-current protection devices mainly include disposable fuses, self-recovery fuses, fusing resistors and circuit breakers, among which the most important over-current protection devices are fuses, also called fuses.

Over-temperature protection devices: mainly include thermistor (WHPPTC), temperature switch and temperature fuse, etc. NTC thermistor type surge suppressors are often used for over-temperature protection in power supply design, because their ability to suppress surge current is equivalent to that of ordinary resistors, but the power consumption on the resistor can be reduced by tens to hundreds of times.

Two. Circuit protection mainly protects the components in the electronic circuit from being damaged by overvoltage, overcurrent, surge, electromagnetic interference, etc. The circuit protection device provides protection for the circuit and chip of the product to ensure that the When the circuit is abnormal, the precision chips and components of the protected circuit will not be damaged. Overvoltage, overcurrent, surge, electromagnetic interference, electrostatic discharge, etc. have always been the focus of circuit protection. Therefore, the mainstream circuit protection devices in the market are also mainly based on lightning protection/overvoltage/overcurrent/anti-static. How to choose the best circuit protection device when selecting the circuit design?

1. You need to know what damage you want to prevent? The first thing you must do is to determine whether you want to prevent direct lightning strikes, secondary shocks , or electrostatic discharge. Once a decision is made, you can choose the appropriate circuit protection device.

2. Decide what result you want when the failure situation occurs? For example, you want to be able to tolerate fault conditions during operation and maintain operation during and after the fault conditions occur; tolerate fault conditions only during shutdown, and then enter operation the next time the device is powered on; or provide protection for the device Safely fail and do not need to operate after the failure is over? The circuit protection device you choose depends on the answers to these questions.

3. Regarding the "normal" and "abnormal" operating conditions, we need to make reasonable assumptions. For example, you cannot choose an overcurrent protection device that operates at 6A, but expect your design to operate normally at 5.99999A. This simply does not have enough margin. If your design consumes 6A current under normal operating conditions, you must choose an overcurrent protection device PTC resettable fuse that operates at 8A or higher current. Not only that, you must understand the maximum operating voltage, the maximum ambient temperature, as well as the fault voltage, fault current and fault duration in order to make the right choice.

4. It must be clear that any protection is impossible to achieve 100%. If you design to protect a specific event, there may always be some more serious events. For example, the hazards described in the telecommunications lightning specifications are much less serious than direct lightning strikes. It is possible to protect products from the hazards caused by direct lightning strikes, but it is very expensive to do so.

5. The circuit protection scheme should be planned at the beginning of the design. Although the circuit protection devices are much smaller than in the past, after the PCB design is completed, it is impossible to add circuit protection devices if there is not enough space.

With the development of science and technology, power/electronic products are becoming increasingly diversified and complicated, and the circuit structure and physical size of electronic products have become smaller and smaller. Circuit protection design in the early stages of the design cycle has become more important. The selection of circuit protection and electronic protection devices may seem low priority, but the design should be started in the early stage to eliminate design problems and ensure the performance and reliability of your products.

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