Electronic circuits are easily damaged during overvoltage, overcurrent, and surge. With the development of technology, the products of electronic circuits are becoming increasingly diversified and complex, and circuit protection becomes particularly important. Circuit protection elements have also changed from simple glass pipe fuses to more types and better protective performance.
What is the significance of circuit protection?
(1) As the integration of circuit boards is getting higher and higher today, the price of the board has also risen with the water, so we must strengthen protection.
(2) Semiconductor device, the working voltage of IC has a lower and lower trend, and the purpose of circuit protection is to reduce energy consumption loss, reduce heating phenomena, and extend the service life.
(3) Due to the conditions for using the environment than ordinary electronic products, the driving conditions of the car are rising, and the driving conditions of the car are very changing. The car generates a large momentary peak voltage when it starts. Therefore, in the power adapter of the supporting products for these electronic equipment, over -voltage protection elements are generally used.
(4) Communication equipment, communication venues have certain requirements for lightning protection. The use of over -pressure protection and overcurrent protection components in these devices is important. They are the key to ensuring that users' personal safety and communication are normal.
(5) The failure of most electronic products is caused by the overvoltage or circuit phenomenon that appears in the electronic equipment circuit. As our quality of electronic equipment is getting higher and higher, the protection Essence
So the circuit protection is so important. What are the common circuit protection elements?
一、Lightning protection device
1.Ceramic gas discharge tube:
The most widely used in lightning protection devices is the ceramic gas discharge tube. The reason why ceramic gas discharge pipes are the most widely used lightning protection device, because whether it is the lightning protection of DC power or lightning protection of various signals, ceramic gas discharge, ceramic gas discharge Tube can play a good protective role.
Its biggest feature is that the flow volume is large, the capacitance is small, the insulation resistance is high, and the range of breakdown voltage is large.
2.Semiconductor discharge tube:
The semiconductor discharge tube is a type of overvoltage protection device. It is made of the principle of the crystal tube. The breakdown current trigger device relying on the PN junction can be turned on and discharged, which can flow over a large wave current or pulse current. The scope of its breakdown voltage constitutes the range of overvoltage protection.
The solid discharge pipe can be directly connected to both ends of the protected circuit. It has the characteristics of accurate lead, fast response (response time NS level), strong wave absorption capacity, two -way symmetry, and high reliability.
3.Glass discharge tube:
Glass discharge tube (powerful discharge tube, torment tube) is a new lightning protection device launched at the end of the 20th century. It also has the advantages of ceramic gas discharge tube and semiconductor overcurrence protector: high insulation resistance (≥10^8Ω), extremely extreme Small capacitors (≤0.8pf), large discharge current (up to 3 kA), two -way symmetry, fast response speed (no lag in impact breakdown)
In addition, the advantages of DC breakdown voltage (up to 5000V), small volume, long life and other advantages. The disadvantage is that the DC breakdown voltage is large (± 20%).
二、over -pressure device
1.Voltage -sensitive resistance:
The pressure -sensitive resistance is also the most used pressure -limited device. Using the non -linear characteristics of the voltage -sensitive resistance, when the overvoltage appears between the poles of the voltage resistance, the voltage resistance can clamp the voltage to a relatively fixed voltage value, thereby achieving the protection of the rear -class circuit.
The response time of the pressure -sensitive resistance is NS level, which is faster than the air discharge pipe, and is slightly slower than the TVS tube. Generally, the overvoltage used for electronic circuits to protect its response speed can meet the requirements. The node capacitance of the pressure -sensitive resistance is generally in the order of several hundred to thousands of PF. In many cases, it is not appropriate to directly apply it in the protection of high -frequency signal lines. When it is used in the protection of AC circuits The current needs to be fully considered when designing the protective circuit. The stamp resistance is large, but smaller than the gas discharge tube.
2.The role of patch pressure -sensitive resistance:
Patch pressure -sensitive resistance is mainly used to protect components and circuits, and prevent ESD generated by power supply, control and signal cables.
3.Transient suppression diode:
The transient inhibitors TVS diode is widely used in the protection of semiconductor and sensitive devices, and is usually used for secondary protection. Basically, it will be used for secondary protection after the ceramic gas discharge tube, and some users directly use it for the first -level protection of the product.
It is characterized by fast reaction speed (PS level), small volume, large pulse power, low clamp voltage, etc. Its 10/1000 μs wave pulse power is from 400W ～ 30kW, and the pulse peak current current is from 0.52A to 544A; the breakdown voltage has a series of values from 6.8V to 550V, which is convenient for various voltage circuits.
三、Overflow device
Self -recovery fuse:
Self -recovery fuse PPTC is an overcurrent electron protection element. Under the condition of high -voltage, high temperature, and vulcanization reactions, it is made of special process processing under high -voltage, high temperature, and vulcanization reactions. Self -recovery fuse (PPTC: polymer self -recovery fuse) is a positive temperature coefficient polymer thermistor that is used for overcurrent protection and can replace the current fuse.
When the circuit is working normally, its resistance value is small (the voltage drops very small). When the circuit has flowed, it increases its temperature, the resistance value increases sharply, so that the current in the circuit is reduced to below the safe value. Therefore, the subsequent circuit is protected, and the automatic recovery is automatically recovered to a low resistance after the overcurrent disappears.
四、static component
1.ESD electrostatic discharge diode:
ESD electrostatic discharge diode is a device for protecting the I/O port protection of high -speed data transmission applications for high -speed data transmission applications. ESD static diode is used to avoid sensitive circuits in electronic devices affected by ESD (static discharge).
It can provide very low capacitors, with excellent transmission line pulse test (TLP) test, and IEC6100-4-2 test capabilities, especially after the multiple sampling is as high as 1000, thereby improving the protection of sensitive electronic components.
2.The role of inductance:
The relationship between electromagnetic is believed to be clear. The role of the inductance is that when the circuit is the beginning, everything is still unstable. If there is a current in the inductance, it will definitely produce an inductive current that is opposite to the current (the law of Faraday electromagnetic induction law. ), After the circuit runs for a while, everything is stable, the current has not changed, and the electromagnetic induction will not generate current. At this time, it will be stable. Safety, like a waterwheel, was slow to turn the resistance at first, and then gradually became peaceful.
3.The role of magnetic beads:
Magnetic beads have high resistivity and magnetic guidance rate. He is equivalent to connecting resistance and inductance, but the resistance and inductance values change with frequency. He has a better high -frequency filtering characteristic than ordinary inductance, and presents resistance at high frequency, so he can maintain high impedance within a relatively wide frequency range, thereby improving the frequency regulating filtering effect. Pass.