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What are the common circuit protection elements

Published time: 2019-11-05

The importance of circuit protection

(1) with the development of electronic products, the function (integration) of IC is increasingly strong, and its "price" is naturally more noble, so it needs to strengthen protection.

(2) in order to reduce power consumption, reduce heat and extend service life, the operating voltage of semiconductor components and IC is getting lower and lower. According to SIA(American semiconductor industry association), the current operating voltage is about 1.5v, and will drop to below 1.2v by 2004, so its ability to resist overcurrent/overvoltage needs to adapt to the new protection requirements.

(3) more and more mobile electronic products, such as handheld, PDA, laptop, camcorder, digital camera, compact disc, etc., these electronic products need battery components as, in the battery components and battery charger must be equipped with protection components.

(4) in modern luxury cars, there are more and more electronic devices, and the working conditions are worse than ordinary electronic products. For example, the driving conditions and environment of the cars are changing rapidly, and great instantaneous peak voltage will be generated when the cars start.Therefore, in the power adapter for these electronic devices, it is generally necessary to install both overcurrent and overvoltage protection components.

(5) many power/electronic products need to prevent lightning strikes and interference between power lines and telephone lines to ensure normal communication and personal safety of users.Therefore, with the development of power/electronic products, the demand for over-current/over-voltage protection components is on the rise.

(6) according to statistics, 75% of the faults in electronic products are caused by over current/over voltage.IBM has analyzed the causes of computer power failures, of which 88.5% were caused by overcurrent/overvoltage.With the demand for electronic product quality, manufacturers must adopt a large number of circuit protection components in order to improve the market competitiveness.

Common circuit protection elements

Lightning protection device

1. Ceramic gas discharge tube

The most widely used lightning protection device is ceramic gas discharge tube. The reason why ceramic gas discharge tube is the most widely used lightning protection device is that no matter it is the lightning protection of dc power supply or various signals, ceramic gas discharge tube can play a good role in protection.Its biggest characteristics are large flow, small capacitance between stages, high insulation resistance, breakdown voltage optional range.

2. Semiconductor discharge tube

Semiconductor discharge tube is a kind of overvoltage protection device, is made of thyristor principle, relying on the PN junction breakdown current trigger device conduction discharge, can flow through a large surge current or pulse current.The range of breakdown voltage constitutes the range of overvoltage protection.Solid discharge tubes can be directly bonded to both ends of the protected circuit when in use.It has the characteristics of accurate conduction, fast response (ns class response time), strong surge absorption, bidirectional symmetry and high reliability.

Semiconductor discharge tube

3. Glass discharge tube

Glass discharge tube (potent discharge tube, prevent detonators) is the end of the 20th century's new lightning protection devices, it has both the advantages of ceramic gas discharge tube and semiconductor overvoltage protector, high insulation resistance (10 ^ 8 Ω or higher), small electrode capacitance (0.8 pF) or less, large discharge current (up to 3 largest ka), two-way symmetry, fast response (no impact breakdown hysteresis), stable and reliable performance, low voltage, after conducting high breakdown voltage and dc (up to 5000 v), the advantages of small volume, long service life.Its disadvantage is that the dc breakdown voltage dispersion is large (±20%).

Overvoltage device

1. Varistors

Piezoresistors are also one of the most used voltage limiting devices.Taking advantage of the non-linear characteristics of the piezoresistor, when the overvoltage appears between the two poles of the piezoresistor, the piezoresistor can clamp the voltage to a relatively fixed value, so as to realize the protection of the rear circuit.The response time of PST is ns level, which is faster than air discharge tube and slightly slower than TVS tube. In general, the response speed of PST for over-voltage protection of electronic circuit can meet the requirements.The junction capacitance of PST is generally in the order of several hundred to several thousand pF. In many cases, it is not suitable to be directly applied in the protection of high frequency signal circuit. When applied in the protection of ac circuit, the junction capacitance is more likely to increase leakage current.The through-current capacity of piezoresistor is larger, but smaller than that of gas discharge tube.


2. Function of patch piezoresistor

Patch piezosensitive resistors are mainly used to protect components and circuits from ESD generated in power supply, control and signal lines.

3. Transient suppression diode

Transient suppressor TVS diode is widely used in semiconductor and sensitive device protection, usually used for secondary protection.Basically, it is used for the secondary protection after the ceramic gas discharge tube, and some users directly use it for the primary protection of the product.It is characterized by fast reaction speed (ps level), small size, large pulse power and low clamping voltage.Its 10/1000 muon pulse power from 400W ~ 30KW, pulse peak current from 0.52A ~ 544A.The breakdown voltages range from 6.8V to 550V, making them easy to use for circuits with different voltages.

Overcurrent devices

1. Self-recovery fuse:

Self-recovery fuse PPTC is a kind of over-current electronic protection element, which is made of high polymer organic polymer in the condition of high pressure, high temperature, vulcan reaction, mixed with conductive particle material, after special processing.Self-recovery fuse (PPTC: polymer self-recovery fuse) is a positive temperature coefficient polymer thermistor, used for overcurrent protection, can replace the current fuse.When the circuit is working normally, its resistance value is very small (the pressure drop is very small). When the over-current of the circuit makes its temperature rise, the resistance value increases sharply by several orders of magnitude, so that the current in the circuit decreases below the safe value, so that the following circuit is protected, and after the over-current disappears, it automatically returns to a low resistance value.

Iv. Electrostatic elements

1. ESD electrostatic discharge diode:

2. Role of inductance:

Electromagnetic believe we all know, the relationship between the circuit inductance effect is in the beginning, everything is not stable, if you have any current through inductor, will produce an induced current in the opposite direction to that of the current (Faraday's law of electromagnetic induction (), wait for circuit operation after a period of time, everything is stable, no change about current, electromagnetic induction, also won't produce current is stable at this time, there will be no sudden changes, to ensure the safety of the circuit, is like a water wheel, due to the resistance to the rotation slowly at first, then gradually tend to be more peaceful.

3. Role of magnetic beads:

Magnetic beads have high resistivity and permeability, which is equivalent to a series of resistors and inductors, but the values of resistors and inductors vary with frequency.It has better high frequency filtering characteristics than ordinary inductance, showing resistance at high frequency, so it can maintain a high impedance over a wide range of frequency, thus improving the effect of FM filtering, used in Ethernet chip.


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