What are the differences between transient voltage suppressor diodes (TVS diodes) and varistors in various aspects?
What are the differences between transient voltage suppressor diodes (TVS diodes) and varistors in various aspects?
Transient voltage suppressor diodes (TVS diodes) and varistors are both electronic components used to suppress overvoltage problems in circuits, but they differ significantly in structure, working principle, characteristics, and applications. This article will compare these two components from several aspects. I. Structure TVS diodes generally use a PN junction or the Zener effect to achieve their suppression effect. Common structures include discrete, series, and parallel structures. A discrete structure combines the diode with a metal gas discharge tube to provide greater power amplification capability. A series structure connects the TVS diode in series with the protected circuit; different voltage protection ranges can be achieved by selecting different diode structures. A parallel structure connects the TVS diode directly in parallel with the protected circuit, achieving a lower protection voltage. A varistor, on the other hand, is a non-linear resistive element made from pressed metal oxide powder. Its structure consists of two electrodes filled with metal oxide powder, such as zinc oxide (ZnO), between the electrodes. When the voltage increases, the quasi-charges of electrons in the metal oxide powder shift from the space quasi-charges between the metal particles, causing a change in resistance. II. Working Principle When a TVS diode operates, if an overvoltage occurs in the protected circuit, its forward voltage, when reaching a certain range, can create a conductive resistive path, dissipating the overvoltage and protecting the protected component. Common operating modes include peak withstand type and peak voltage type. When a varistor operates, its resistance decreases as the voltage increases, thus suppressing overvoltage by consuming its energy. When the voltage drops to a certain level or becomes too high, the varistor returns to its high resistance state. III. Characteristics and Parameters 1. Response Time: The response time of a TVS diode is typically in the nanosecond range, exhibiting extremely fast response speed and rapidly suppressing overvoltage; while the response time of a varistor is relatively long, typically in the millisecond range. 2. Resistance Characteristics: TVS diodes operate in a high-resistance state under normal conditions. When the voltage exceeds the rated value, they break down instantaneously, reducing their resistance and significantly increasing the conduction current, thus suppressing overvoltage. Varistors, on the other hand, have very high conductivity at high voltages and extremely low resistance, enabling them to absorb and dissipate overvoltages. 3. Protection Capability: TVS diodes typically have high suppression capability and can handle larger power overvoltages; varistors usually operate within a lower power range and have weaker overvoltage suppression capability for high power. 4. Overvoltage Recovery Capability: After suppressing an overvoltage, a TVS diode can automatically return to its original resistance state and provide overvoltage protection again; a varistor, however, may be damaged and melt due to excessive overvoltage, requiring replacement. IV. Application Areas: TVS diodes are mainly used in circuits requiring fast response and high suppression capability, such as power supply protection, communication surge protection, and electronic equipment. Their high suppression capability and fast response characteristics make them commonly used overvoltage protection components. Varistors are primarily used in circuits where voltage suppression requirements are relatively low, such as power supply filtering, electrostatic discharge (ESD) suppression, and overvoltage protection in analog, digital, and communication circuits. In summary, both transient voltage suppressor diodes and varistors are electronic components used to suppress overvoltage problems in circuits, but their structures, operating principles, characteristics, and application areas differ significantly. When selecting a varistor, the appropriate protection component must be chosen based on the specific application requirements.
