What are the packaging forms of varistors?

Complete Analysis of Varistor Packaging Forms: A Deep Guide from Form to Scene
Varistor, as a common surge suppression component in circuits, its packaging form directly affects power carrying capacity, installation convenience, and environmental adaptability. The following provides packaging selection references from three dimensions: packaging classification, feature comparison, and selection logic, combined with typical application scenarios.
1、 Classification of varistor packaging: Dual dimensions of form and power
1. Plug in packaging (Radial Leaded)
Typical size characteristics of packaging types
Circular package with a diameter of 5~20mm, early standard package, suitable for high-power surge protection (such as 14D471K)
Square package 7 × 7~20 × 20mm optimized heat dissipation structure, suitable for high-voltage scenarios (such as 20mm square pieces, with a withstand voltage of up to 1000V)
Bolt type packaging with M3~M8 thread for high-power industrial applications, such as power equipment (such as 40kA level varistors, requiring heat dissipation fins)
2. Surface mount packaging (SMD)
Typical size characteristics of packaging types
0805/1206 2.0 × 1.25mm low-power ESD protection, suitable for portable devices (such as 0805 package, current capacity<1kA)
1210/1812 3.2 × 1.6mm medium power universal package, balancing power and volume (such as 1210 package, current capacity 2-5kA)
2920/4032 7.8 × 5.0mm high-power surge protection, such as industrial power supply (such as 2920 package, current capacity 10-20kA)
3. Special packaging form
Typical size characteristics of packaging types
Customized size integrated aluminum heat sink with heat sink package, suitable for high-power pulses (such as new energy inverters, current capacity>50kA)
Epoxy resin encapsulation with a waterproof and moisture-proof design ranging from 10 to 30mm, suitable for outdoor equipment such as streetlight controllers
Modular design of array packaging with multiple varistors in parallel, suitable for three-phase power protection (such as 3P+N array modules)
2、 Comparison of key packaging characteristics: the core basis for selection
1. Power carrying capacity
Plug in packaging: Bolt type (M8) with a current capacity of up to 100kA, suitable for lightning protection;
Surface mount packaging: The 2920 package has a current carrying capacity of approximately 15kA and is suitable for industrial power surges;
Heat dissipation performance: Plug in heat dissipation is achieved through pins, while surface mount heat dissipation relies on PCB copper plating. Additional heat dissipation design is required for high-power scenarios.
2. Parasitic parameter influence
Pin inductance: Plug in pin inductance>10nH may limit high-frequency response;
Distributed capacitance: Square packaged capacitance<100pF, suitable for high-speed signal line protection.
3. Environmental adaptability
Epoxy resin encapsulation: IP67 protection level, salt spray resistance, UV resistance;
Bolt type packaging: Strong anti vibration performance, suitable for ships and mining equipment.
3、 Typical application scenarios and packaging selection
1. Consumer electronics (power adapters, chargers)
Requirement: miniaturization and low cost.
Recommended packaging:
Input end: 1210 patch type (such as 1210-14D471K, with a current capacity of 2kA);
Output terminal: 0805 patch type (such as 0805-07D471K, ESD protection).
2. Industrial control (PLC, motor drive)
Requirement: High reliability and vibration resistance.
Recommended packaging:
Power input: Bolt type M5 (such as M5-20mm square piece, with a current capacity of 40kA);
I/O interface: 1812 patch type (such as 1812-14D471K, Cj=50pF).
3. New energy (photovoltaic inverters, energy storage systems)
Requirements: High power, weather resistance.
Recommended packaging:
DC side: packaged with heat sink (such as 40mm square plate+aluminum heat sink, with a current capacity of 60kA);
Communication side: Encapsulated with epoxy resin (such as a 30mm circular disc, IP67 protection).
4. Communication equipment (base station, switch)
Requirement: High frequency response, low loss.
Recommended packaging:
Signal line: 1206 patch type (such as 1206-07D471K, Cj=80pF);
Power module: 2920 patch type (such as 2920-14D681K, with a current capacity of 15kA).
4、 Misconceptions and Solutions in Packaging Selection
Misconception 1: Blindly pursuing high-power packaging, ignoring cost and space
Consequence: Occupying too much PCB area in small devices.
Improvement: Select the minimum necessary packaging based on the actual surge current (such as IEC 61000-4-5 test level).
Misconception 2: Choosing high capacitance packaging for high-frequency signal lines
Consequence: Increased signal reflection and higher error rate.
Improvement: For GHz level signals, choose the 1206/0805 package with Cj<50pF.
Misconception 3: Neglecting environmental adaptability design
Consequence: Outdoor equipment may experience leakage and failure of varistors due to humidity.
Improvement: For humid environments, priority should be given to epoxy resin encapsulation or IP67 protection level products.
5、 Summary: Encapsulation Selection Decision Tree
Determine power demand:
Flow rate<5kA → choose patch type (1210/1812);
Flow rate>10kA → plug-in type (bolt type/square plate) is required.
Evaluate signal rate:
Speed<100Mbps → Acceptable Cj=100pF;
Speed>1Gbps → Cj<50pF is required.
Consider environmental conditions:
Outdoor/high humidity → choose epoxy resin encapsulation;
Vibration scene → Priority plug-in packaging.
Through systematic selection, it is possible to ensure that varistors exhibit optimal protective performance in specific scenarios, while balancing cost and reliability requirements.