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The functions of eight common basic circuit protection devices are summarized

2020-05-19
Circuit protection components application field widely, as long as there is electricity is necessary to install the circuit protection components, such as various types of home appliances, home audio and video and digital products, personal care, such as consumer electronics, computer and its peripheral, mobile phone and its surrounding, lighting, medical electronics, automotive electronics, electric power, industrial equipment, etc., covering all aspects of the production and living.

There are two main forms of circuit protection: overvoltage protection and overcurrent protection. Selecting appropriate circuit protection device is the key to realize efficient and reliable circuit protection design. When selecting circuit protection devices, it is important to know that the protection circuit should not interfere with the normal behavior of the protected circuit, and that it must prevent any voltage transients from causing repetitive or non-repetitive instability of the entire system.

Lightning protection overvoltage devices are divided into clamp type overvoltage devices and switching type overvoltage devices, switching type overvoltage devices are known as the lightning protection devices: ceramic gas discharge tube, semiconductor discharge tube and glass discharge tube; Clamp type overvoltage devices include transient suppression diode, piezosensitive resistor, SMT piezosensitive resistor and ESD discharge diode. The PTC element self-recovery fuse is the main part of the overcurrent device. The following is its specific function:

1. Function of discharge tube

Discharge tube is often used in the multistage protection circuit of the first or the first two stages, to discharge the lightning transient overcurrent and limit the overvoltage, discharge tube is to limit the voltage at a lower level, so as to play a protective role. Discharge tube of shuo kai electron is divided into gas discharge tube and solid discharge tube. The gas discharge tube is mainly composed of ceramic gas discharge tube and glass gas discharge tube. The type and type of discharge tube in specific application shall be determined by the engineer according to the protection grade of the application port and relevant selection parameters.

2, the role of transient diode

The transient suppression diode can change the high impedance between the two poles into the low impedance at the speed of 10 to the power of minus 12 seconds, absorb up to several kilowatts of surge power, and make the voltage between the poles clamp at a predetermined value, effectively protecting the precise components in the electronic circuit from the damage of various surge pulses.

3, the role of varistor

Piezoresistor (piezoresistor) is a voltage limiting protection device. In circuit protection, the nonlinear characteristics of piezoresistor are mainly used. When overvoltage appears between the two poles of piezoresistor, the piezoresistor can clamp the voltage to a relatively fixed voltage value, so as to realize the protection of the backward circuit.

4. Function of patch piezoresistor

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

5. Role of ESD electrostatic discharge diode

ESD electrostatic discharge diode (ESD) is an overvoltage, anti-static protection device 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 ESD (electrostatic discharge). Offers very low capacitance, excellent transmission line pulse (TLP) testing, and iec6100-4-2 testing capabilities, especially with multi-sample Numbers up to 1000, to improve protection of sensitive electronic components.

6. Function of PTC self-restoring fuse

When the circuit works normally, its resistance value is very small (voltage drop is very small). When the circuit overflows and makes its temperature rise, the resistance value increases sharply by several orders of magnitude, reducing the current in the circuit to below the safe value, thus protecting the later circuit. After troubleshooting, the PPTC element will soon cool down and return to its original low resistance state, allowing it to work again like a new PPTC element.

7. The 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 a 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. Inductance is also a function of dc, resistance to ac, this is not used much, I am not quite clear how to use, and so on to share with you

8. The effect of magnetic beads

A magnetic bead has a high resistivity and permeability, which is equivalent to a series of resistors and inductors, but the resistance and inductance vary with frequency. It is better than ordinary inductance high-frequency filtering characteristics, at high frequency resistance, so it can maintain a high impedance in a wide range of frequencies, so as to improve the frequency modulation filtering effect, used in Ethernet chips.

Let's talk about the basics of diodes - classification, applications, properties, principles, parameters

Characteristics and applications of diodes

Almost in all electronic circuits, all need to use semiconductor diode, it plays an important role in many circuits, it is one of the earliest semiconductor devices, its application is also very wide.

Application of diodes

1, rectifier diode

The alternating current in alternating direction can be converted into pulsating dc current in a single direction by using the one-way conductivity of the diode.

2. Switching components

Diode in the forward voltage action resistance is very small, in the conduction state, equivalent to a switch on; Under the action of the reverse voltage, the resistance is very large, in the cut-off state, like a disconnected switch. The switching characteristics of diodes can be used to form various logic circuits.