Circuit protection components have a wide range of applications. Wherever electricity is used, there is a need for installing circuit protection components. These are found in various consumer electronics such as household appliances, home audio-visual and digital products, personal care products, computers and their peripherals, mobile phones and their peripherals, lighting, medical electronics, automotive electronics, power systems, industrial equipment, and more. They cover all aspects of people’s production and life.

Circuit protection mainly comes in two forms: overvoltage protection and overcurrent protection. Choosing appropriate circuit protection devices is crucial for achieving efficient and reliable circuit protection designs. When it comes to selecting circuit protection devices, it is necessary to understand the functions of each type of circuit protection device. When selecting circuit protection devices, we must be aware that the protection circuit should not interfere with the normal behavior of the protected circuit. Additionally, it must prevent any voltage transients from causing repetitive or non-repetitive unstable behavior of the entire system.

Lightning protection and overvoltage devices are divided into clamping overvoltage devices and switching overvoltage devices. Switching overvoltage devices are the well-known lightning protection devices: ceramic gas discharge tubes, semiconductor discharge tubes, and glass discharge tubes. Clamping overvoltage devices include transient voltage suppressor diodes (TVS), varistors, chip varistors, and ESD discharge diodes. Overcurrent devices are mainly PTC (Positive Temperature Coefficient) self-resetting fuses. Here are their specific functions:

1. Discharge Tubes: Discharge tubes are often used in the first or first two stages of multilevel protection circuits to discharge lightning transient overcurrents and limit overvoltages. They protect by limiting the voltage to a lower level. The discharge tubes from Shuokai Electronics are further divided into gas discharge tubes and solid-state discharge tubes. Gas discharge tubes mainly include ceramic gas discharge tubes and glass gas discharge tubes. The selection of discharge tube types and models for specific applications requires engineers to determine based on the protection level of the product application port and relevant selection parameters.

2. Transient Voltage Suppressor Diodes (TVS): TVS diodes can change the high impedance between their two poles to low impedance at a speed of 10^-12 seconds, absorbing surge power up to several kilowatts and clamping the voltage between the two poles to a predetermined value, effectively protecting precision components in electronic circuits from damage caused by various surge pulses.

3. Varistors: Varistors are voltage-limiting protection devices. In circuit protection, they mainly utilize the nonlinear characteristics of varistors. When overvoltage appears between the two poles of the varistor, the varistor can clamp the voltage to a relatively fixed voltage value, thereby protecting the subsequent circuits.

4. Chip Varistors: Chip varistors are mainly used to protect components and circuits from ESD generated in power supply, control, and signal lines.

5. ESD Electrostatic Discharge Diodes: ESD electrostatic discharge diodes are overvoltage and antistatic protection components designed for I/O port protection in high-speed data transmission applications. ESD protection devices are used to protect sensitive circuits in electronic equipment from the effects of ESD (electrostatic discharge). They provide very low capacitance and excel in transmission line pulse (TLP) testing and IEC 61000-4-2 testing capabilities, especially after multiple sampling up to 1000, thereby improving protection for sensitive electronic components.

6. PTC Self-resetting Fuses: When the circuit operates normally, its resistance is very small (voltage drop is very small). When an overcurrent occurs in the circuit, causing it to heat up, the resistance increases sharply by several orders of magnitude, reducing the current in the circuit to below a safe value, thereby protecting the subsequent circuits. When the fault is cleared, the PTC component cools down quickly and returns to its original low-resistance state, ready to work like a new PTC component.

7. Inductors: Everyone is familiar with the relationship between electromagnetism. The role of inductors is that at the beginning of the circuit, when everything is still unstable, if there is current passing through the inductor, it will definitely generate an induced current opposite to the direction of the current (Faraday’s Law of Electromagnetic Induction). After the circuit has been operating for some time and everything stabilizes, with little change in current, electromagnetic induction will not generate current, and the circuit becomes stable, avoiding sudden changes and ensuring circuit safety. This is like a waterwheel that rotates slowly due to resistance at first and then gradually stabilizes. Another role of inductors is to pass direct current and block alternating current. This is not used much, and I am not quite sure how to use it specifically. I will share with you when it is used.

8. Ferrite Beads: Ferrite beads have high resistivity and permeability. They are equivalent to resistors and inductors in series, but both the resistance value and inductance value change with frequency. They have better high-frequency filtering characteristics than ordinary inductors, presenting resistance at high frequencies, so they can maintain high impedance over a wide frequency range, thereby improving frequency modulation and filtering effects. They have been used on Ethernet chips.

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