Aumov LV Ultramov Varistor Design Guide Page 13 Varistor Design Guide For DC & Automotive Applications

DC Application Varistor Design Guide 2015 Littelfuse DC Application Varistor Design Guide How to Select a Low Voltage DC MOV Example of MOV selection process for surge protection: Circuit conditions and requirements: 24VDC circuit Current waveform for surge is 8/20 s; voltage is 1.2/50 s Peak current during the surge is 1,000A Requirement is to survive 40 surges Other components (control IC, etc.) are rated to withstand 300V maximum. Approach to finding a solution: To find the voltage rating of the MOV, allow for 20% headroom to account for voltage swell and power supply tolerances. 24V DC 1.2 = 28.8V DC So look at 31V DC rated MOVs Determine which MOV disc size to use - identify those that minimally meet the 1,000A surge requirement. - Use the Pulse Rating Curves in the LV UltraMOV Varistor Series datasheet to determine pulse capabilities of each series per the 40 pulses @ 1,000A requirement - Use V-I Curve in the datasheet of the selected MOV to verify that the peak voltage will be below the 1,000V ceiling. How to Select a Low Voltage DC MOV 12

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