What type of diode is commonly used for surge protection in communication rooms?

1. Analysis of Surge Threat in Communication Room
The surge threats faced by communication rooms come from a wide range of sources, mainly including the following aspects:
Lightning induction: Lightning is one of the most powerful surge sources in nature. When lightning strikes buildings, lines, or the ground near the communication room, it will generate strong induced overvoltage and overcurrent on the communication lines and equipment, posing a serious threat to the equipment in the room.
Power grid fluctuations: Abnormal situations such as voltage fluctuations, instantaneous interruptions, and harmonics in the power grid may also cause communication room equipment to be impacted by surges. For example, the start and stop of large equipment in the power grid, as well as faults in the power system, can cause sudden changes in grid voltage, resulting in surges.
Equipment switch: During the switching process of various equipment in the communication room, such as power switches, equipment start and stop, transient overvoltage and overcurrent may also occur. Although these surges are relatively small, long-term accumulation can also cause damage to the equipment.
The hazards of surges to communication room equipment mainly manifest as:
Equipment damage: Excessive voltage and current may penetrate the insulation layer of the equipment, damage electronic components, and cause the equipment to malfunction.
Data loss: Surge may interfere with the normal operation of equipment, resulting in data transmission errors or losses, affecting the quality of communication services.
System paralysis: Severe surge impact may cause the entire communication system to collapse, resulting in huge economic losses and social impacts.
2. Common types and characteristics of surge protection diodes
(1) Ceramic Gas Discharge Tube (GDT)
Ceramic gas discharge tube is a protective device with the highest flow rate, which has the advantages of large flow rate, high inter electrode insulation resistance, small inter electrode capacitance, and low leakage current. Its conductivity is formed by gas ionization, which requires a large amount of energy to excite, so its response speed is the slowest among all overvoltage protection devices. In communication rooms, ceramic gas discharge tubes are commonly used for lightning protection of high-speed communication lines, such as coaxial cables, telephone line interfaces, high-definition video interfaces, Ethernet ports, etc. For example, DOWOSEMI's monolithic ceramic gas discharge tube devices can achieve 100kA (8/20 μ s) and withstand large surge current impacts.
(2) Varistor (MOV)
Varistors are semiconductor voltage limiting surge devices made by sintering zinc oxide as the material. It has excellent nonlinear characteristics, super surge absorption capacity, no freewheeling, and low cost advantages, and is widely used in electronic circuits for surge overvoltage protection. The current carrying capacity of varistors is second only to ceramic gas discharge tubes, with a response speed of nanoseconds, making them suitable for lightning protection of AC power lines and low-frequency signal lines. The single unit current capacity of Dongwo varistor can reach 70kA (8/20 μ s), and the varistor voltage can reach 1800V. However, due to the lattice structure, varistors are prone to aging during long-term use, which affects their protective performance.
(3) Transient suppression TVS diode
The full name of TVS diode is Transient Voltage Suppressor, commonly referred to as Transient Voltage Suppressor or Surge Protection Diode in Chinese. It is a special semiconductor protection device mainly used to protect electronic devices from transient overvoltage and current surges.
Working principle: When the two poles of a TVS diode are subjected to a reverse transient high-energy impact, such as an abnormal overvoltage in a circuit, the diode can quickly convert the high impedance between its two poles into low impedance (on the order of 10 ^ -12 seconds). This change enables TVS diodes to absorb surge power of up to several kilowatts and clamp the voltage between the two poles at a predetermined or lower level, effectively protecting precision components in electronic circuits from damage caused by surge pulses.
Features: TVS diodes have the advantages of fast response speed, low clamping voltage, high voltage accuracy, and small size. It is generally packaged with patches or plugins and is commonly used for surge protection of DC power lines or low-speed communication lines. In communication products, TVS diodes are commonly used to protect signal lines with high transmission rates and large transient currents, preventing data loss and equipment failures. For example, in the protection of high-speed data interfaces such as USB 3.0 and HDMI, low capacitance ESD protection diodes (a special form of TVS diode) should be prioritized to avoid negative impact on signal quality.
Type segmentation: There are various types of TVS diodes based on their packaging form and application scenarios. For example, SMB packaged TVS includes SMBJ series, TPSMBJ series, etc; SMC packaged TVS includes SMCJ series, TPSMCJ series, etc. TVS diodes with different packaging may have differences in power capacity, response time, etc. Users can choose according to their actual needs.
(4) Other types of diodes
Semiconductor Discharge Tube (TSS): TSS is a surge protection device with negative resistance characteristics. Due to its special PN-PN junction structure design, TSS can achieve several times higher current carrying capacity than TVS of the same size and voltage on the same chip area, while its capacitance is several times smaller than TVS of the same specification. It can be used for surge protection of some communication lines, such as RS485, RS232, CAN bus, etc. TSS has a high cost-effectiveness and is an ideal choice for surge protection in low-speed communication lines.
ESD electrostatic protection diode: ESD electrostatic protection diode is a specially designed anti-static protection component, which is a TVS array with a specific circuit layout composed of multiple diodes or TVS combinations. Its conduction time is slower than TVS, and the electrostatic discharge is generally nanosecond level pulses with relatively less destructive power. Therefore, the chip grain area of ESD devices is also smaller, which can achieve small and miniaturized packaging. Through circuit structure design, the minimum junction capacitance of ESD devices can be reduced to a few tenths of picofarads, making them suitable for ESD protection of high-speed data lines such as HDMI, USB 3.0, IEEE 1394, etc.
3. Suggestions for selecting surge protection diodes
(1) Clarify circuit protection requirements
Before selecting surge protection diodes, it is necessary to clarify the specific protection requirements of the circuit, including the operating voltage range of the protected circuit, signal polarity, signal frequency, and possible transient overvoltage threats. For example, for a digital circuit with a working voltage of 3.3V, it is necessary to select a protective diode that can withstand the voltage range and consider the possible ESD impact and voltage surge that the circuit may be subjected to.
(2) Key parameter considerations
Reverse working peak voltage (VRMM): The reverse working peak voltage of the protective diode must be higher than the maximum working voltage of the protected circuit to ensure that the protective diode will not conduct under normal working conditions, thereby not affecting the normal operation of the circuit.
Clamping voltage (VC): Clamping voltage is the lowest level at which a protective diode can suppress voltage when subjected to transient overvoltage. A lower clamping voltage means more effective protection, so a protection diode with a clamping voltage lower than the withstand voltage of the protected device should be selected.
Dynamic resistance (RDYN): Dynamic resistance reflects the current limiting ability of the protective diode when conducting. A lower dynamic resistance helps to better suppress overvoltage and improve protection effectiveness.
Current carrying capacity: Select a protective diode with sufficient current carrying capacity based on the potential surge current that the circuit may face. The current carrying capacity of different types of diodes varies greatly, with ceramic gas discharge tubes having the highest current carrying capacity and TVS diodes having relatively smaller current carrying capacity.
(3) Considering practical application conditions
In practical applications, factors such as the installation location of protective diodes, circuit layout, and environmental conditions also need to be considered. For example, in harsh environments such as high temperature and humidity, it is necessary to choose protective diodes with good environmental adaptability. Meanwhile, for some special applications such as automotive electronics, medical equipment, etc., it may be necessary to choose protective diodes that comply with specific industry standards and certifications.
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