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Varistor Selection Tips

Dongguan Weiqing Electronics Co.,Ltd | Updated: Jan 30, 2019
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七乐彩预测最准十专家nominal voltage selection

generally speaking, the varistor is used in parallel with the protected device or device. under normal conditions, the dc or ac voltage across the varistor should be lower than the nominal voltage, even when the power supply fluctuation is the worst. the maximum continuous operating voltage selected in the rated value, the nominal voltage value corresponding to the maximum continuous operating voltage value is the selected value. for overvoltage protection applications, the varistor voltage should be greater than the actual circuit voltage. generally, use the following formula to select: vma=av/bc where: a is the circuit voltage fluctuation coefficient, generally 1.2; v is the circuit dc working voltage; 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 is 1.5 times of the dc operating voltage, and the peak value is also considered in the ac state. the calculation result should be expanded by 1.414 times. in addition, you must also pay attention to the selection:


七乐彩预测最准十专家(1) it must be ensured that the continuous operating voltage will not exceed the maximum allowable value when the voltage fluctuation is maximum, otherwise the service life of the varistor will be shortened;

(2) when a varistor is used between the power supply line and the ground, the voltage between the line and the ground may rise due to poor grounding. therefore, a varistor with a higher nominal voltage than the line-to-line use is usually used. the surge current absorbed by the varistor should be less than the maximum flux of the product.


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