Varistors, also known as varistors or varistors, are nonlinear voltage dependent resistive devices whose resistance values vary with the voltage applied at both ends. The main material of varistors is metal oxides, such as zinc oxide (ZnO), which are widely used in electronic circuits to protect sensitive electronic devices from voltage spikes and surges.

Structural features:

Metal oxide particles: The core of a varistor is a polycrystalline structure composed of small metal oxide particles (such as ZnO), which form complex conductive paths between them.

Electrodes: There are usually metal electrodes at both ends, used to connect to a circuit.

Packaging: There is usually an insulated packaging on the outside to protect the internal structure and provide mechanical strength. The packaging material can be plastic, epoxy resin, or other insulation materials.

working principle:

When the voltage applied to both ends of the varistor is below a certain threshold (called "breakdown voltage" or "clamp voltage"), the varistor exhibits a very high resistance value and is almost non-conductive. Once the voltage exceeds this threshold, the resistance value of the varistor will sharply decrease, allowing a large amount of current to flow, thereby absorbing overvoltage energy and protecting other components in the circuit from damage. After the voltage drops, the varistor will return to a high resistance state and be ready to act again.

Usage scenario:

Varistors are mainly used in the following areas:

Power protection: At the input end of the power supply, it is used to prevent voltage surges caused by lightning strikes or other reasons from damaging the circuit.

Communication line protection: Used to protect equipment from transient voltage on communication lines such as telephone lines and network lines.

Household appliance protection: In household appliances such as televisions, computers, etc., it is used to protect internal circuits from voltage fluctuations.

Industrial control equipment: In industrial control systems, used to protect sensitive control and measurement equipment.

Selection and application precautions:

Rated voltage: When selecting, the appropriate rated voltage varistor should be selected based on the maximum working voltage of the circuit.

Maximum allowable current: Select a varistor with sufficient capacity based on the possible maximum surge current.

Response time: Consider whether the response time of the varistor is fast enough to effectively protect the circuit.

Energy absorption capacity: Select the appropriate energy absorption capacity of the varistor based on the size of the energy impact that the circuit may experience.

Size and packaging: The size and packaging of varistors can vary greatly depending on different application requirements and manufacturer designs. Varistors are usually used to absorb transient voltage surges, so their size is often related to the amount of energy they can handle. The following are some common sizes and packaging types of varistors:

Axial Lead Type:

This type of varistor has two leads and is commonly used in traditional through-hole mount (THT) circuit boards.

The size range can range from a very small 2mm x 1.2mm to a larger 14mm x 52mm.

Common external dimensions include: 0402, 0603, 0805, 1206, 1210, 1812, 2220, etc. These dimensions are usually expressed in English units (inches), corresponding to lengths and widths of 0.04 "x 0.02", 0.06 "x 0.03", 0.08 "x 0.05", 0.12 "x 0.06", 0.12 "x 0.10", 0.18 "x 0.12", and 0.22 "x 0.20", respectively.

Radial Lead Type:

This type of varistor also has two leads, but the leads extend from the same side, making it suitable for compact installation space.

The size can range from a few millimeters to several tens of millimeters, depending on the power and energy processing capacity.

Common sizes include: 5mm, 7mm, 10mm, 14mm, 20mm and other diameters, with lengths typically ranging from a few millimeters to several tens of millimeters.

Surface Mount Type:

This type of varistor has no leads and is directly mounted on the surface of the circuit board, making it suitable for high-density assembly.

Dimensions are usually smaller, and common sizes include: 0402, 0603, 0805, 1206, 1210, 1812, etc. These dimensions are also expressed in English units.

Surface mount varistors are suitable for automated production lines as they can be quickly and accurately placed on circuit boards.

High Power Type:

For applications that require handling higher power and energy, varistors may have larger dimensions and special packaging, such as metal casings with heat sinks.

The size of these large varistors may exceed 50mm or even larger, depending on the application requirements.

When selecting a varistor, in addition to considering size and packaging, factors such as rated voltage, maximum allowable current, energy absorption capacity, response time, and environmental adaptability should also be considered. Manufacturers usually provide detailed specification sheets and technical information to help designers choose suitable varistors.