Dec. 17, 2021
Varistor is a resistance device with nonlinear volt-ampere characteristics. It is mainly used for voltage clamping when the circuit is subjected to overvoltage and absorbing excess current to protect sensitive devices. Before choosing a varistor, you should first understand the following related technical parameters: Nominal voltage refers to the voltage value across the varistor under the specified temperature and DC current. Leakage current refers to the current value flowing in the varistor when a continuous DC voltage is applied under the condition of 25°C.
Grade voltage refers to the voltage peak value that appears at both ends of the varistor when it passes 8/20 grade current pulses. The flow rate is the peak current when a predetermined pulse current (8/20μs) waveform is applied. Surge environment parameters include large surge current Ipm (or large surge voltage Vpm and surge source impedance Zo), surge pulse width Tt, small time interval Tm between two adjacent surges, and presets in the varistor during the working time, the total number of surge pulses N etc.
Generally speaking, varistors are often used in parallel with the protected device. Under normal circumstances, the DC or AC voltage across the varistor should be lower than the nominal voltage, even when the power supply fluctuates badly, the voltage shouldn’t be higher than the large continuous working voltage selected in the rated value. The nominal voltage value corresponding to the large continuous working voltage value is the selected value.
For the application of overvoltage protection, the varistor voltage value should be greater than the voltage value of the actual circuit. Generally, the following formula should be used for selection: VmA=av/bc where: a is the circuit voltage fluctuation coefficient, generally 1.2; v is the circuit DC working voltage (effective value when AC); b is the varistor voltage error, generally 0.85; c is the aging coefficient of the component, generally 0.9; the actual value of VmA calculated in this way is 1.5 times of the DC working voltage. The peak value is also considered in the state, so the calculation result should be enlarged by 1.414 times.
The above content is what you need to know when choosing a varistor.Hopefully the content of this article can help you. Dongguan Zhixu Electronic Co., Ltd. (also JYH HSU(JEC)) has a full range of varistor and capacitor models with guaranteed quality. JEC has passed ISO9001:2015 quality management system certification; JEC safety capacitors (X capacitors and Y capacitors) and varistors have passed national certifications of the main industrial powers across the world; JEC ceramic capacitors, film capacitors and super capacitors are in compliance with environmental protection indicators.
We have over 30 years of manufacturing experience. If you have technical questions or need samples, please contact us.
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