Varistors, serving as critical protective elements within electronic circuits, assume a central role. Their utility spans three key areas: safeguarding against overvoltage, shielding from lightning, and fulfilling the prerequisites of safety evaluations. These functions allow varistors to offer indispensable protection across a variety of applications, including over-voltage safeguarding, lightning defense, surge current mitigation, peak pulse absorption, voltage clamping, extinguishing high-voltage arcs, eradicating noise, and the safeguarding of semiconductor devices.
At the heart of a varistor lies zinc oxide, a semiconductor ceramic composite made predominantly of metal oxide. The foundational unit of a varistor is formed by zinc oxide granules and the high-resistance layers that surround them. The granules of zinc oxide exhibit low resistivity, whereas the boundary layers show considerably higher resistivity. The interaction between two adjoining zinc oxide granules creates a potential barrier akin to that of a Zener diode, illustrating the operational principle of an individual varistor unit. By connecting these units in series and parallel configurations, a varistor's matrix is constructed, enabling its protective capabilities.
In the swiftly evolving realm of electronic technology, the application spectrum of varistors continues to expand. Varistors are available in a multitude of specifications and models tailored to diverse operational needs, with the JEC series offering variants like 05D, 07D, 10D, 14D, 20D, 25D, 32D, among others. Each model caters to specific requirements across different scenarios.
Turning to technical parameters, a varistor’s performance is encapsulated by several critical metrics:
Nominal voltage (varistor voltage) pertains to the voltage across the varistor under a defined temperature and the influence of a DC current.
Leakage current represents the current flow through the varistor when subjected to a steady DC voltage at a standard ambient temperature of 25°C.
Clamping voltage describes the peak voltage across the varistor when it encounters a level 8-20 current pulse.
Peak current capability indicates the maximum current the varistor can withstand under a specified pulse current condition (8-20μs waveform).
Surge parameters include surge current (Ipm), surge voltage (Vpm), and surge source impedance (Zo), among other environmental factors.