1. What is circuit protection?
Circuit protection is a process of protecting circuits from abnormal conditions and faults by taking measures and applying specific devices. It is designed to protect chips, components, equipment and systems in electronic circuits from damage caused by overcurrent, overvoltage, short circuit, overtemperature, ESD electrostatic interference and other adverse factors.

Circuit protection usually includes various combinations of circuit protection components and corresponding EMC/EMI control measures, such as ceramic gas discharge tubes, semiconductor discharge tubes, TVS transient suppression diodes, varistors, resettable fuses, PLED open circuit protectors, etc. These devices can detect abnormal conditions in the circuit and quickly cut off the current or clamp the voltage within a safe voltage range to prevent overloading, short circuiting, etc. of components in the circuit. Through circuit protection, the normal operation and safety of the circuit can be ensured.

2. Types of circuit protection
Circuit protection can be divided into the following types:

Overcurrent protection: Overcurrent protection is a common circuit protection method used to prevent components in the circuit from being overloaded. It can detect when the current exceeds a set value and quickly cuts off the current to prevent components in the circuit from being damaged.
Overvoltage protection: Overvoltage protection is used to prevent components in a circuit from being damaged by excessive voltage. It can detect when the voltage exceeds a set value and protect components in the circuit by breaking the circuit or diverting the voltage.
Short-circuit protection: Short-circuit protection refers to protective measures to prevent short-circuit faults in circuits. When a short circuit occurs in the circuit, the short circuit protection device will quickly cut off the current to protect the components in the circuit from damage.
Over-temperature protection: Over-temperature protection is used to prevent components in the circuit from being damaged due to overheating. It can monitor the temperature in the circuit and take appropriate measures when the temperature exceeds the set value, such as cutting off the current or reducing the power.
Voltage fluctuation protection: Voltage fluctuation protection is used to prevent components in a circuit from being damaged by sudden voltage changes or transient voltage fluctuations. It can protect circuits from voltage fluctuations through filtering, voltage stabilization, etc.

3. The significance of circuit protection
Circuit protection is of great significance:

Protect equipment and components: Circuit protection can effectively protect equipment and components in the circuit from damage caused by overload, short circuit, over-temperature and other factors. This helps extend the life of the equipment, reduces equipment repair and replacement costs, and ensures circuit reliability and stability.
Prevent fires and accidents: Circuit protection can promptly detect and cut off current under abnormal conditions to avoid fires and other safety accidents caused by overheating, short circuits and other issues. It helps protect personal safety and property security.
Improve circuit reliability: By taking appropriate circuit protection measures, the reliability and stability of the circuit can be improved. The protection device can respond quickly and cut off the current under abnormal conditions to prevent the components in the circuit from being damaged, thereby ensuring that the circuit continues to operate normally.

Compliance with standards and specifications: Circuit protection is one of the requirements for compliance with engineering standards and specifications. Various industries and fields have corresponding circuit protection requirements and guidance, such as power systems, buildings, automobiles, etc. By implementing appropriate circuit protection measures, the requirements of relevant standards and specifications can be met.
Reduce repair time and costs: Circuit protection can help quickly locate and resolve circuit faults. When a problem occurs in the circuit, the protection device will quickly cut off the current, reducing the scope of component damage and simplifying the troubleshooting process. This saves repair time and costs.

4. Commonly used circuit protection devices or combinations
In order to achieve better circuit protection effects, circuit protection is usually completed through a single protection device product or a combination of multiple products:

Ceramic gas discharge tube: The gas discharge tube is sealed in a ceramic package and consists of two or several metal electrodes with gaps inside, filled with inert gas. When the voltage applied to the two electrode ends reaches the point where the gas in the gas discharge tube breaks down, the gas discharge tube begins to discharge and changes from high resistance to low resistance, so that the voltage across the electrodes does not exceed the breakdown voltage. It is often used in the first or first two stages of multi-level protection circuits to discharge lightning transient overcurrent and limit overvoltage.

Semiconductor discharge tube: The semiconductor discharge tube is made based on the thyristor principle. It relies on the breakdown current of the PN junction to trigger the device to conduct and discharge, and can flow a large surge current or pulse current. The range of its breakdown voltage constitutes the range of overvoltage protection. When used, the solid discharge tube can be directly connected across the two ends of the protected circuit. Semiconductor discharge tubes are widely used in program-controlled switches, telephones, fax machines, patch panels, XDSL, communication interfaces, communication transmitting equipment and other fields that require lightning protection in communication switching equipment to protect the IC inside them from instantaneous Overvoltage impact and damage.

TVS diode: The working principle of TVS diode is similar to that of common Zener diode. When it withstands a high-energy instantaneous overvoltage pulse, its working impedance can immediately drop to a very low conduction value, allowing large currents to pass through and clamping the voltage to a predetermined level, thereby effectively protecting precision components in electronic circuits. The device is protected from damage. Can be used in DC or AC circuits.

Varistor: A varistor is a special resistance device with nonlinear volt-ampere characteristics. It uses zinc oxide as the main raw material, adds a variety of trace metal oxides, and is a new type of ideal device that is mixed, molded, and sintered. Overvoltage protection device, its conductivity value changes non-linearly with the change of applied voltage. The varistor is not a real resistor, but a component with transient voltage suppression function. Generally, there is no positive and negative pole. It is different from TVS. When used, it is also connected in parallel with the protected IC or circuit. The response time of the varistor will be slower than that of TVS.

Self-recovery fuse: When an abnormal overcurrent passes through the self-recovery fuse, the heat generated causes the polymer organic polymer to expand, and the conductive particles wrapped in the polymer organic polymer will separate, thus cutting off the conductive channel of the PTC and causing the PTC resistance to rise. , reducing the abnormal overcurrent; when the abnormal overcurrent fault is cleared, the high molecular organic polymer of the PTC shrinks to its original shape and reconnects the conductive particles, and the conductive channel is restored and the PTC resistance returns to its original low resistance state.

Static suppressor: It has fast response and low clamping voltage performance, and has an extremely low capacitance value, which can effectively reduce the signal loss caused by the parasitic capacitance of the protection device itself. It is very suitable for use in high-speed signal transmission ports; it also has It has superior properties such as extremely low leakage current (<0.1nA) and high electrostatic shock resistance. Compared with other protection devices, it has excellent cost performance. It is the best choice for electrostatic protection of high-speed data transmission ports such as USB, HDMI, Display port, E-SATA and IEEE1394.

About Semiware
Semiware has a complete product lineup of circuit protection devices, with a total number of standardized products of 6,000+; the company relies on its R&D technology in the semiconductor field and application technology of end products to provide services to global customers in the electronics, automotive and industrial markets. Has more than 1,000 employees. For more information, please visit the Semiware website: https://semiware.com.