Created by: Glen Zhu | Updated Date: March 25th, 2025
The basic function of a surge protector is to absorb or divert excessive voltage to protect electronic equipment from damage. However, just knowing its existence and basic function is far from enough.
Understanding the internal components and working principles of surge protectors can not only help us choose the right protector but also ensure its effective operation in practical use. A high-quality surge protector is not simply a “black box,” but a system composed of multiple precision components, each playing an indispensable role in the protection process.
By gaining a deep understanding of these components, users can make wise decisions when purchasing, avoiding protection failures due to incorrect selection or improper use.
The core components of surge protectors include the following key parts, each playing a unique role in the protection process, collectively forming its overall function:
These components work together to form the overall function of surge protectors: MOV and TVS absorb and limit surge energy, GDT diverts protection in extreme cases, grounding systems ensure safe discharge of electrical energy, while the casing enhances reliability and user experience.
Using the Type 1 Surge Protector FLP25-275/3S+1 product as an example, via the following video that provides a detailed understanding of the components of a surge protector.
Metal Oxide Varistor (MOV)
Metal Oxide Varistor (MOV)
MOV is the most common component in surge protectors and is considered the “main force”. It is made of metal oxide materials and has nonlinear resistance characteristics: it presents high impedance under normal voltage, quickly changes to low impedance when the voltage exceeds its threshold, absorbing excess electrical energy.
The main function of MOV is to limit the voltage received by equipment, prevent it from exceeding the safe range, and absorb surge energy.
MOV is a kind of semiconductor device, usually made of zinc oxide (ZnO) particles and a small amount of other metal oxides (such as bismuth, manganese), forming multiple tiny PN junctions in its internal structure. This material characteristic causes the resistance value of MOV to significantly change with the applied voltage:
1. Under normal voltage: Within the normal operating voltage range of the device, MOV presents a high impedance state (very high resistance), almost non-conductive, with no significant impact on the circuit.
2. Surge occurrence: When external voltage (such as surges) exceeds the breakdown voltage of MOV (threshold voltage), its internal PN junction rapidly conducts, and the resistance value sharply decreases from a high impedance state to a low impedance state.
3. Energy absorption and dissipation: At this point, MOV diverts excess current brought by surges, absorbs surge energy through itself, dissipates it in the form of heat energy, while limiting the voltage at both ends of the device to keep it within a safe range.
Due to its unique voltage-resistance characteristics, MOV has become the preferred component for surge protectors. It can effectively respond to surges caused by lightning strikes, power fluctuations, etc., and is widely used to protect household appliances (such as TVs, computers), industrial equipment, and communication systems from damage or malfunctions caused by overvoltage.
Although MOV is powerful, its performance is not unlimited. After experiencing multiple surges, MOV may age and its resistance characteristics gradually decrease, so regular inspection or replacement is necessary.
In addition, MOV cannot handle continuous overvoltage situations and may need to be used in conjunction with other protective measures (such as fuses) in certain scenarios to ensure comprehensive circuit protection.
Gas Discharge Tube (GDT)
Gas Discharge Tube (GDT)
Gas Discharge Tube (GDT) is a key auxiliary component in surge protectors, specifically designed to handle extreme surges, such as ultra-high voltage surges caused by lightning strikes. The structure of GDT is a sealed glass or ceramic tube filled with low-pressure inert gas (such as argon or neon), with electrodes at both ends.
When the externally applied voltage exceeds the breakdown voltage of GDT, the gas inside the tube ionizes, forming a low-impedance conductive channel. This conductive channel can quickly divert surge currents to the grounding system, protecting equipment from surge damage.
GDT has the following outstanding capabilities when dealing with extreme surges:
In actual surge protector design, GDT is usually used in conjunction with Metal Oxide Varistor (MOV) to form a multi-level cooperative protection system. Depending on the connection method, the combination of GDT and MOV can be divided into the following two configurations:
1. Series configuration
In series design, GDT is typically placed in front of MOV, acting as the “first line of defense”. When a high-energy surge occurs, GDT is triggered first to quickly shunt most of the surge current and reduce voltage. Subsequently, the remaining energy is further absorbed and limited by MOV.
This configuration effectively reduces the burden on MOV, prolongs its service life, especially in environments with frequent surges.
2. Parallel configuration
In parallel design, GDT and MOV work independently to share different protective tasks. MOV handles medium-sized surges to limit voltage and protect equipment; while GDT activates during extreme surges (such as lightning strikes), providing an additional shunting path to prevent MOV from failing due to overload.
This combination utilizes the fast response of MOV and high-energy tolerance characteristics of GDT to achieve comprehensive protection effects.
Transient Voltage Suppressor (TVS)
Transient Voltage Suppressor (TVS)
TVS is a fast-acting semiconductor device that can respond to surges in nanoseconds, making it particularly suitable for protecting sensitive electronic devices such as communication equipment and computer interfaces. It limits voltage to safe levels through clamping action, protecting small components in circuits.
TVS is a semiconductor device based on the avalanche breakdown effect, usually a special Zener diode with unidirectional or bidirectional conduction characteristics. Its working principle can be divided into the following stages:
1. Normal operation state
In the normal voltage range, TVS is in a high impedance state, with extremely high resistance and almost no conductivity, having no impact on circuit operation.
2. Surge occurrence
When external voltage (such as electrostatic discharge or transient surge) exceeds the breakdown voltage of TVS (also known as clamping voltage), its internal PN junction will quickly undergo avalanche breakdown. At this time, TVS switches from high impedance to low impedance state with very short response time.
3. Voltage clamping and current diversion
In the low impedance state, TVS diverts surge currents to the ground system, rapidly reducing overvoltage in the circuit. At the same time, it clamps the voltages at both ends of equipment to a safe preset level, protecting downstream sensitive components from damage.
4. Return to normal
After surges end, TVS automatically returns to high impedance state without external intervention to continue monitoring circuits and prepare for next surge event.
TVS’s outstanding feature is its extremely fast response speed, typically in the picosecond (ps) to nanosecond (ns) range. This feature allows it to activate protection mechanisms in a very short time after a surge occurs, much faster than other common surge protection devices such as metal oxide varistors (MOV) or gas discharge tubes (GDT).
Due to this ultra-fast response capability, TVS is particularly suitable for protecting time-sensitive equipment, such as:
Although TVS has a significant advantage in response speed, its energy tolerance is relatively low, so it is often used for protection against low-energy surges or as a supplement to high-energy absorption components such as MOV and GDT to provide more precise protection.
The grounding system provides a safe discharge path for surge currents, and is an indispensable part of surge protectors. Whether it’s MOV, GDT or TVS, when absorbing or diverting surges, excess electrical energy needs to be directed into the ground to prevent damage to equipment. A good grounding design is the foundation of overall efficiency.
Its core functions include the following aspects:
Diverting surge currents
When components in surge protectors (such as metal oxide varistor MOV, gas discharge tube GDT or transient voltage suppressor diode TVS) detect overvoltage, they quickly redirect excess current to the grounding system.
The grounding system prevents these surge currents from flowing towards protected equipment by directing them into the ground, thus avoiding damage to equipment due to overload or breakdown.
Voltage stabilization
A good grounding system can maintain voltage stability in circuits and reduce the impact of voltage fluctuations caused by surges on equipment. This is particularly important for sensitive electronic devices because voltage fluctuations can lead to performance degradation or permanent damage.
Safely discharging static and induced charges
The grounding system can effectively discharge accumulated static or induced charges in the system, preventing these charges from accumulating inside equipment and avoiding potential risks of arcing or spark discharges.
Through the above functions, the grounding system has become an indispensable core link in surge protectors. It is not only the “exit” for surge currents but also a key guarantee for ensuring the safe operation of equipment.
The quality of the grounding system directly determines the protective effect of surge protectors. Here are several key aspects of how grounding quality affects overall efficiency:
Grounding resistance
Grounding resistance is an important indicator for measuring the effectiveness of a grounding system. The lower the resistance, the faster surge currents can be discharged to the ground, resulting in better protection.
According to international standards (such as IEC 62305), it is recommended that grounding resistance be below 4 ohms to ensure rapid and safe diversion of surge currents.
If the grounding resistance is too high, current diversion efficiency will decrease, leading to inadequate performance from surge protectors and potentially exposing equipment to overvoltage risks.
Grounding path
The design of a grounding path directly affects diversion efficiency. A short and direct grounding path can reduce resistance and inductance, thereby increasing the discharge speed of surge currents.
Conversely, long or curved paths will increase impedance and reduce protection effectiveness. Therefore, optimizing the grounding path is an important measure for enhancing surge protector efficiency.
Quality of grounding materials
The long-term stability and reliability of a grounding system depend on the materials used. High-quality grounding materials (such as copper wire or ground rods) have good conductivity and corrosion resistance, maintaining stable performance under various environmental conditions.
Low-quality materials may lead to failure due to aging or corrosion, weakening the protective capabilities of surge protectors.
Maintenance of the grounding system
Grounding systems require regular inspection and maintenance to ensure they remain in good condition at all times. For example, loose connections or increased ground resistance can reduce diversion efficiency.
Regular maintenance work can help identify and address potential issues promptly, ensuring continuous effectiveness from surge protectors.
As the external protective layer of surge protectors, the selection and design of the enclosure directly affect the durability and safety of the equipment. The main functions of the enclosure include:
1. Physical protection
The enclosure can protect internal components from external environmental influences, such as:
High-quality enclosure materials (such as flame-retardant plastics or metal alloys) can effectively resist harsh environments, ensuring stable operation of internal components.
2. Heat dissipation and temperature control
When absorbing surge energy, surge protectors generate heat, so the enclosure needs to have good heat dissipation performance to avoid overheating and damaging components. Some high-end enclosure designs also come with heat dissipation holes or fins to further optimize temperature management.
3. Electrical insulation
The enclosure material needs to have excellent electrical insulation performance to prevent leakage or short circuits, ensuring user safety. Especially in humid or dusty environments, insulation performance is particularly important.
4. Durability and aging resistance
High-quality enclosure materials can resist factors such as ultraviolet rays, temperature changes, and chemical corrosion, extending the service life of equipment.
For surge protectors exposed for long periods outdoors or in extreme environments, durable enclosure are especially crucial.
LSP’s Surge Protection Device is Integrating LKD MOVs, Vactech GDTs, and reinforced flame-retardant materials provide multi-tiered protection with all the surge SPDs needed.
Regarding issues related to SPD (surge protection device) components, we warmly welcome you to contact us at any time. Whether you have any questions or needs, we will do our best to provide you with professional answers and technical support, ensuring the safety of your equipment. We look forward to your inquiry!
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