1. Overview of 20D Series

1.1 Functions

• Overvoltage Clamping: Conducts rapidly when the applied voltage exceeds the varistor voltage, clamping the voltage to a safe level.

• Surge Absorption: Absorbs 8/20μs surges generated by lightning strikes, switching operations and inductive loads, with peak current ranging from 3 kA to 10 kA.

• ESD & Noise Suppression: Eliminates static electricity and high-frequency spike interference.

• Non-polar & Bidirectional Protection: Compatible with both AC and DC circuits.

1.2 Model Naming Rule (Example: 20D471K)

• 20: Chip diameter of 20 mm

• D: Disc type

• 471: Varistor voltage V₁ₘₐ = 47 × 10¹ = 470 V

• K: Tolerance ±10%

2. General Electrical & Environmental Parameters

• Varistor Voltage (V₁ₘₐ): 18 V ~ 1800 V

• Continuous AC Voltage (Uₐc): 14 ~ 750 VAC

• Continuous DC Voltage (U_dc): 18 ~ 970 VDC

• Surge Current (Iₚ, 8/20μs): 3 kA / 5 kA / 10 kA

• Single Pulse Energy (E): 100 ~ 400 J (increases with voltage rating)

• Response Time: < 25 ns

• Leakage Current (I_L): < 20 μA (measured at 0.75 U_dc)

• Junction Capacitance (Cⱼ): Hundreds to thousands pF (higher for low-voltage models)

• Operating Temperature: −40 ℃ ~ +85 ℃ (+105 ℃ for partial models)

• Storage Temperature: −40 ℃ ~ +125 ℃

• Insulation Resistance: ≥ 500 MΩ

• Temperature Coefficient: −0.5%/℃

• Safety Certifications: CQC, VDE, UL, RoHS

3. Dimensions (Radial Leaded, Unit: mm)

• Chip Diameter: 20.0 ± 0.5

• Body Thickness: 5.1 ~ 8.9 (increases with voltage rating)

• Lead Diameter: 0.8 ± 0.1

• Lead Spacing (Standard): 10 ± 0.5

4. Typical Applications

• Lightning protection and surge suppression for AC/DC power input terminals

• Household appliances, industrial control boards, electric meters and lighting drivers

• Reverse surge absorption for coils of relays, contactors and solenoid valves

• ESD protection for communication ports, RS485/RS232 interfaces and network ports

• High-side protection for photovoltaic systems, inverters and charging piles

5. Selection Guidelines

1. The rated Uₐc / U_dc shall be 1.1 ~ 1.2 times the continuous operating voltage of the circuit.

2. Select Iₚ according to 8/20μs surge level. 5 kA is the most common choice; 10 kA is recommended for harsh environments.

3. Pay attention to junction capacitance in low-voltage signal circuits to avoid signal bandwidth degradation.

4. For voltage ratings above 1000 V, prioritize high-energy / enhanced types for improved reliability.