Aumov LV Ultramov Varistor Design Guide Page 15 Varistor Design Guide For DC & Automotive Applications

DC Application Varistor Design Guide 2015 Littelfuse DC Application Varistor Design Guide www.littelfuse.com Determine if the 14mm LV UltraMOV Varistor Surge Rating is sufficient to meet the requirements: 1. Using the Repetitive Surge Capability (Pulse Rating) Curves in the LV UltraMOV Varistor datasheet, locate the pulse with (20s) on the x-axis (see Fig 1 for 14mm MOV and Fig 2 for 20mm MOV). This signifies an 8/20 sec waveform shape. 2. Find where the vertical line intercepts the 1,000A point, which is our required surge rating for 40 hits. 3. In this case, we find that the 14mm LV UltraMOV Varistor can only survive a little more than 10 hits. However, the 20mm choice can survive 100 pulses. Therefore, we select the more conservative choice, which is the 20mm MOV (V20E25P). Determine if the 20mm LV UltraMOV varistor is suitable to meet the clamping requirements: 1. Locate the peak current on the X-axis (1000A) in the LV UltraMOV varistor V-I curve. 2. Find where it intercepts the curve for the V20E25P product. 3. In this case, the maximum clamping voltage is at 130V, which is beneath the 300V damage threshold for the sensitive components in the circuit. Our LV UltraMOV varistor selection will protect us to the correct level. Conclusion: The V20E25P can meet the 24V DC, 1000A, 40-hit 8/20s surge requirement with clamping voltage at 130V. Maximum Clamping Voltage for 20mm Parts 10 10 10 10 10 10 10 10 Peak Amperes (A) 200 300 100 30 20 Maximum Peak Volts (V) V20x11P - V20x40P 40 50 60 70 80 90 -3 -2 -1 0 1 2 3 4 V20x14P V20x17P V20x20P V20x25P V20x11P MAXIMUM CLAMPING VOLTAGE MODEL SIZE 20mm How to Select a Low Voltage DC MOV (continued) 14

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