Basic Description

Working Principle and Performance Advantages

Selection and Application Guide

Full-Scene Protection Solutions

Maintenance and Testing Tips

Pros and Cons Analysis & Selection Strategy

Frequently Asked Questions

A varistor is a voltage-sensitive resistor. Its main job is to stop transient surge voltage. When the voltage goes over a set limit, the varistor quickly turns into a low-resistance state. It turns extra energy into heat and protects the device behind it.

Most varistors use zinc oxide (ZnO) as the base material. They often have a multilayer ceramic structure, which lets them absorb twice as much energy as traditional single-layer types.They come in different package types like through-hole and surface-mount to fit various needs.

The varistor works like a semiconductor. It uses the barrier at the ZnO grain boundary. At low voltage, the barrier gives high resistance. When voltage goes over the threshold (for example, 480V ±10%), the barrier breaks down, and resistance drops 1000 times. It reacts in just 5 nanoseconds (ns).(By comparison, a TVS diode reacts in 8–10 ns)During a surge, one standard varistor can absorb up to 300J of energy. That equals 90% reduction of a 10kV lightning surge.Its multilayer structure improves energy dissipation by 40%. It works well in high-frequency surge conditions.

Advantage 1:

Compared to gas discharge tubes, varistors do not need ignition voltage. They can block a wide voltage range from 20V to 50kV. This cuts down setup costs by 60%.

Three key parameters to check:

• Rated Voltage (V₁mA) should be 20% higher than the system’s max working voltage.
• Clamping Voltage must be lower than the max limit of the protected device.
• Energy capacity should follow IEC 61051 standard grades.

Application Suggestions:

• AC Power Line: Use large-size, high-voltage types (e.g., TDK AVR40 series).
• Signal Lines: Use low-capacitance (<100pF) surface-mount varistors.
• Industrial Devices: Use vibration-resistant packages with UL certification.

Advantage 2:

For USB 3.0 interface protection, a varistor saves 75% PCB space compared to a TVS diode. It also raises ESD (Electrostatic Discharge) level to ±30kV.

Power Systems:

• Place a varistor in parallel at AC input. It limits a 1.2/50μs surge to under 600V.
• Use with resettable fuse in DC power lines for double protection.

Precision Instruments:

• HDMI ports can use low-capacitance varistors in 0402 size (capacitance <5pF). This keeps 10Gbps signal clean.
• Industrial PLCs use triple-electrode lightning varistors, tested by IEC 61643-11.

Advantage 3:

In motor drive circuits, a varistor works for 1000 surge cycles. A gas discharge tube only lasts 50 cycles. This gives 5 times longer maintenance time.

Warning Signs of Failure:

• Surface cracks or color change
• Leakage current over 20μA (measured at rated voltage)
• Temperature rise more than 15°C above room temperature

Test every 2 years:

• Use a multimeter. A good varistor shows resistance >1MΩ.
• Use a pulse generator. Clamping voltage should stay within ±5%.
• Use infrared camera. Heat should spread evenly.

Main Advantages:

• Fast response: 5–25ns
• Low cost: ¥0.1–5 each, good for large quantity
• Voltage range: 0.1kV–100kV

Limitations:

After 100 surges, clamping voltage may shift by 10%

Leakage current increases if temperature goes over 85°C

Needs to work with a fuse to prevent short circuits

What is a varistor?

A varistor is a two-terminal electronic component made of semiconductor material. It exhibits non-ohmic characteristics where its electrical resistance varies dynamically with applied voltage, demonstrating a nonlinear current-voltage relationship. This device is alternatively known as a VDR (voltage-dependent resistor) in technical contexts.A varistor is a two-terminal electronic component made of semiconductor material. It exhibits non-ohmic characteristics where its electrical resistance varies dynamically with applied voltage, demonstrating a nonlinear current-voltage relationship. This device is alternatively known as a VDR (voltage-dependent resistor) in technical contexts.

How to test a varistor?

Begin by safely isolating the varistor from the circuit before inspection. Subsequently, position the multimeter's test leads across its opposing terminals. Conclude the process by briefly making contact with the probes in quick succession.

What is a varistor used for?

A varistor is an electrical device that shields circuits against abrupt voltage surges by automatically limiting excessive voltage to a predetermined safety threshold during overvoltage events.

What is the difference between a fuse and a varistor?

A fuse functions as a series-connected component intended to break an electrical circuit during overcurrent conditions. In contrast, a varistor operates in parallel within a circuit, exhibiting variable resistance that responds to changes in voltage levels.

What is the disadvantage of varistor?

The drawbacks of varistors primarily involve three aspects. Firstly, they tend to develop higher leakage currents as they undergo aging or operate under elevated temperatures. Secondly, their performance deteriorates over time when subjected to prolonged thermal stress or repeated surge incidents. Thirdly, these devices exhibit constrained capabilities regarding their maximum current-handling capacity.