What are the common circuit protection components? The role of safety protection circuits

Due to the presence of some unstable factors in the power circuit, a circuit designed to avoid these unstable factors affecting circuit efficiency is called a protection circuit. For example, overcurrent protection, overvoltage protection, overheating protection, full load maintenance, overcurrent protection, etc. The products of electronic circuits are becoming increasingly diverse and complex, and circuit protection has become crucial. The circuit protection components have also evolved from simple glass tube fuses to a large number of types, with better protection characteristics.

The role of safety protection circuits

In various electronic devices, setting overvoltage protection and overcurrent protection has become increasingly important. Specifically, the role of safety protection circuits

(1) Due to the increasing integration of circuit boards and the rising prices of boards, maintenance needs to be strengthened.

(2) For semiconductor devices, the working voltage of ICs is getting lower and lower, and the effect of circuit protection is to save energy, reduce consumption, reduce heating phenomena, and extend service life.

(3) On board devices, due to more extreme usage scenarios compared to ordinary electronic devices, the driving conditions of the vehicle have changed, and a large instantaneous peak voltage is generated when the car starts. Therefore, overvoltage protection components are usually applied in the adapters of these electronic product supporting equipment.

(4) Communication equipment and communication sites have certain requirements for lightning surge protection, and the application of overvoltage protection and overcurrent protection components has become crucial to ensuring customer safety and normal communication.

(5) Most malfunctions in electronic devices are caused by overvoltage or circuit conditions in electronic product circuits. As our requirements for the quality of electronic products become increasingly high, the maintenance of electronic circuits has become increasingly indispensable.

So circuit protection is so important, what are the common circuit protection components? Today, we will introduce several categories to you.

1、 Lightning protection device

1. Porcelain gas discharge tube:

Porcelain gas discharge tubes are the most commonly used lightning protection devices. The reason why porcelain gas discharge tubes are the most commonly used lightning protection device is because porcelain gas discharge tubes can play a certain protective role, whether it is a DC power supply or various signals.

The biggest characteristics are high flow rate, small interstage capacitance, high insulation resistance, strong breakdown field, and a wide range of options.

2. Semiconductor discharge tube:

Semiconductor discharge tube is an overvoltage protection device made using the principle of thyristor. With the help of PN junction through current trigger, it can pass through a large amount of surge current or pulse current. Its powerful breakthrough field forms the category of overvoltage protection.

The solid-state discharge tube can directly cross both sides of the receiving protection circuit. It has precise disconnection and fast response (response speed of ns level), strong surge absorption ability, double symmetry, and high stability.

3. Glass discharge tube:

Glass discharge tubes (strong discharge tubes, lightning protection tubes) are new lightning protection devices introduced in the early 20th century. They have the advantages of ceramic gas discharge tubes and semiconductor overvoltage protectors: high insulation resistance (≥ 10 ^ 8 Ω), small interpole capacitance (≤ 0.8pF), large discharge current (up to 3) kA), dual symmetry, fast reaction speed (no impact penetration lag), safe and reliable characteristics, and low voltage after on/off,

In addition, there is a DC breakdown field (up to 5000V), small size, and long service life. The disadvantage is that the DC breakdown field has strong permeability (± 20%).

2、 Overvoltage device

1. Varistor:

Varistor is also one of the most commonly used voltage limiting devices. Using the nonlinear characteristics of Varistor, when the overvoltage occurs between the two poles of Varistor, Varistor can position the Voltage clamp to a relatively fixed voltage value, so as to achieve subsequent power supply maintenance.

The response speed of Varistor is ns level, faster than that of gas discharge tube and slower than that of TVS tube. Generally speaking, the response speed used for overvoltage protection of electronic circuits can meet the requirements. The junction capacitance of Varistor is generally in the range of hundreds to thousands of pf. In many cases, it should not be directly used for the maintenance of high-frequency signal lines. When used for protection of AC circuits, due to the increased leakage current caused by its junction capacitance, it is necessary to fully consider when planning the protection circuit. The Varistor has a large flow capacity, but it is smaller than the gas discharge tube.

2. Efficacy of patch Varistor:

The SMD Varistor is mainly used to protect components and circuits to avoid ESD generated by power supply, control and power line.

3. Diode transient suppression:

Transient suppressor TVS diodes are widely used in the maintenance of semiconductors and sensitive devices, and are generally used for secondary protection. Basically used for secondary protection after ceramic discharge tubes, some users directly use it for primary protection of products.

It is characterized by fast reaction speed (ps level), small size, large Pulsed power, low voltage, etc. 10/1000 μ Wave Pulsed power is 400W~pulse peak current is 30KW 0.52A~544A; The breakdown field strength is greater than the 6.8V~550V series value, making it convenient for various circuit applications with different voltages.

3、 Overcurrent device

1. Self recovery fuse:

The self restoring fuse PPTC is an overcurrent electronic protection component. Under high pressure, high temperature, and vulcanization reaction conditions, conductive particle materials are added to polymer organic polymers and made through special processes. Self recovery fuse (PPTC: polymer self recovery fuse) is a positive temperature coefficient polymer thermistor used for overcurrent protection, which can replace current fuses.

When the circuit is operating normally, its resistance value is very small (voltage drop is very small). When the circuit is overcurrent, it warms up and the resistance value sharply increases by several orders of magnitude, reducing the current in the circuit to below the safe value, thus maintaining the circuit. After the overcurrent disappears, it returns to the low resistance value.

4、 Electrostatic component

1. ESD electrostatic discharge diode:

ESD electrostatic discharge diode is an overvoltage and anti-static protection component, which is a customized device for maintaining I/O ports for high-speed data transmission. ESD electrostatic diodes are used to prevent sensitive circuits in electronic products from being affected by ESD (electrostatic discharge).

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

2. The function of inductance:

The electromagnetic relationship must be clear. The role of inductance is that everything is unstable at the beginning of the circuit. If the inductance contains current, it will produce opposite induced current (Faraday's law of induction). Until the circuit runs for a period of time, everything is stable, the current does not change, and the electromagnetic induction will not produce current. At this time, it is stable and will not change suddenly. Therefore, it ensures the safety of the power supply, just like a waterwheel. At first, due to the slow rotation of resistance, it gradually calmed down.

3. The efficacy of magnetic beads:

Magnetic beads have high resistance and permeability, equivalent to a series connection of resistance and inductance, but the resistance and inductance values vary with frequency. It has better high-frequency filtering characteristics than ordinary inductors, and has resistance at high frequencies. Therefore, it can maintain high resistance over a very wide operating frequency band, thereby improving the frequency modulation filtering effect used on Ethernet chips.

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