What are commonly used circuit protection components?

Electronic circuits are easily damaged by overvoltage, overcurrent, power surges, etc. With development of technology, electronic circuit products are becoming more diverse and complex, and circuit protection is becoming more important. Circuit protection components have also changed, from simple glass tube fuses to more types and superior protection performance.

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What does chain protection mean?

In all kinds of electronic products, installation of overvoltage protection and overcurrent protection is becoming more and more important, so what is importance of circuit protection? Let me talk to you today:

(1) As level of PCB integration is getting higher and higher, price of boards is also going up, so we need to strengthen protection.

(2) The operating voltage of semiconductor devices and integrated circuits is getting lower and lower, and purpose of circuit protection is to reduce power loss, reduce heat generation, and increase service life.

(3) Vehicle-installed equipment Due to harsher environment than conventional electronic products, driving environment of vehicle is constantly changing, and when vehicle is started, a large instantaneous peak voltage is generated. Therefore, surge protection components are commonly used in power adapters to support products of these electronic devices.

(4) Communication equipment and communications equipment have certain requirements for lightning protection and surge protection. It becomes important to use surge and overcurrent protection components in this equipment. They must ensure personal safety of users and normal communication. essential.

(5) Most of failures of electronic products are caused by overvoltage or short circuit phenomena in circuit of electronic equipment. As we have more and more high quality requirements for electronic equipment, protection of electronic circuits also can no longer be ignored.

So, circuit protection is so important, what are commonly used circuit protection components? Today I will introduce you to some.

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Lightning protection device

1. Ceramic Discharge Tube:

Ceramic discharge tube is most widely used lightning protection device The reason why ceramic discharge tube is most widely used lightning protection device is that whether it is DC power supply lightning protection or various signal lightning protection, ceramic discharge tubes can play very good protective role.

Its main features are high flow, small interstage capacitance, high insulation resistance and a wide range of breakdown voltages.

2. Semiconductor gas discharge tube:

The semiconductor gas discharge tube is a kind of surge protection device, which is based on principle of thyristor. It is based on breakdown current of PN junction, which triggers device to conduct and discharge, and can carry a large surge current. or impulse current. Its breakdown voltage range is surge protection range.

When using a solid gas discharge tube, it can be directly connected to two ends of circuit to be protected. It has characteristics of accurate conduction, fast response (response time at ns level), strong pulse absorption ability, bi-directional symmetry and high reliability.

3. Glass Discharge Tube:

The glass discharge tube (powerful discharge tube, anti-knock) is a new lightning protection device released at end of 20th century. It has advantages of both ceramic discharge tube and semiconductor surge protector: high insulation resistance (≥ 10^8 ohm ), small interelectrode capacitance (≤0.8pF), large discharge current (up to 3kA), bidirectional symmetry, fast response (no shock breakdown hysteresis), stable and reliable performance, low voltage after conduction Low .

In addition, it has advantages of high DC breakdown voltage (up to 5000V), small size and long service life. Its disadvantage is that DC breakdown voltage has a large spread (±20%).

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Surge protector

1. Varistor:

The varistor is also most widely used voltage limiting device. Using non-linear characteristics of varistor, when an overvoltage occurs between two poles of varistor, varistor can limit voltage to a relatively fixed voltage value, thereby realizing protection of downstream circuit.

The response time of varistor is ns, which is faster than gas discharge tube and slightly slower than TVS tube. It is generally used to protect electronic circuits from overvoltage, and its response speed can meet requirements. The junction capacitance of varistors is typically in hundreds to thousands of pF. In many cases, it is not suitable for direct application in protection of high-frequency signal lines. When used in protection of AC circuits, because large junction capacitance increases leakage current when designing protection circuit. The bandwidth of varistor is greater, but less than that of a gas discharge tube.

2. Chip varistor function:

Chip varistors are mainly used to protect components and circuits from electrostatic discharge in power, control and signal lines.

3. Transient suppression diode:

TVS diodes for transient suppression are widely used for protection of semiconductors and sensitive devices, usually for secondary protection. It is mainly used for secondary protection after ceramic gas discharge tube, and some users use it directly for primary protection of product.

It features fast response (ps level), small size, high pulse power and low clamping voltage. Its 10/1000 µs wave pulse power is from 400W to 30kW, and peak pulse current is from 0.52A to 544A; breakdown voltage has a range of values ​​from 6.8 V to 550 V, which is convenient for use in circuits with various voltages.

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Overcurrent device

1. Resettable fuse:

The PPTC resettable fuse is an electronic overcurrent protection component. It is made from high molecular weight organic polymers under conditions of high pressure, high temperature and vulcanization reaction. After adding conductive particle materials, it is processed by a special process. Resettable fuse (PPTC: polymer resettable fuse) is a positive temperature coefficient polymer thermistor used for overcurrent protection, can replace current fuse.

During normal operation of circuit, its resistance value is very small (the voltage drop is very small), when circuit is overcurrent and its temperature rises, resistance value increases sharply by several orders of magnitude, so that current in circuit decreases to a safe level Below value to subsequent circuit has been protected, and it will automatically return to a low resistance value after overcurrent disappears.

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Electrostatic components

1. Electrostatic Discharge Diode ESD:

The ESD electrostatic discharge diode is a surge and static protection component and device designed to protect I/O ports in high-speed data applications. Electrostatic ESD diodes are used to protect sensitive electronic equipment circuits from effects of ESD (electrostatic discharge).

It can achieve very low capacitance, has excellent transmission line pulse (TLP) test and IEC6100-4-2 test capability, especially after multiple sampling up to 1000, thus improving protection of sensitive electronic components.

2. Role of inductance:

I think everyone knows relationship between electromagnetism. The role of inductance is that at beginning of circuit, when everything is still unstable, if a current passes through inductance, induced current opposite to direction of current will be generated (Faraday's law of electromagnetic induction), after circuit has been running for a certain period of time, everything is stable , current has not changed, and electromagnetic induction will not generate current. At this time, it will be stable and there will be no abrupt changes, to ensure safety of circuit compromised, like a water wheel that is first slowly rotated due to resistance, and then gradually calms down.

3. The role of magnetic beads:

Magnetic beads have high resistivity and permeability, which is equivalent to a series connection of resistance and inductance, but both resistance and inductance change with frequency. It has better high-frequency filtering performance than ordinary inductors. It is resistive at high frequencies, so it can maintain high impedance over a wide frequency range, thus improving FM filtering effect. Applied on Ethernet. Pass chips.