Aumov LV Ultramov Varistor Design Guide Page 12 Varistor Design Guide For DC & Automotive Applications

2015 Littelfuse DC Application Varistor Design Guide DC Application Varistor Design Guide Telecom/SPD Application + - In telecom power applications, multiple LV UltraMOVTM varistors are used in a single SPD to provide surge protection. Several varistors are connected in parallel to provide the desired level of energy handling. The varistors are connected in series with a GDT to provide additional transient protection to earth/ground. Outdoor Low Voltage Application Security System/LED Protection Load AC/DC 12V/24V/48V DC Output 12V/24V AC/DC Input Industrial/Process Control Application Inductive Surge Protection 28V DC + C L R C C L R C = Stray Capacitance = Relay Coil Inductance = Relay Coil Resistance Telecom Power Supply Units (PSUs) typically range from 36VDC to 72VDC on the high end of the voltage range. The LV UltraMOV varistor can be used for applications where the voltage is less than 125VDC. Low Voltage Surge Protective Device (SPD) modules are used in telecom and industrial applications to provide module-based surge protection of complete systems. 12VAC/DC and 24VAC/VDC are the voltages commonly used for security system components such as motion sensors, IP cameras, and DVRs. Demand for energy savings is helping to drive the adoption of LED lighting. LED light bulbs powered at 24V are widely used for home and commercial applications. The use of LV UltraMOV varistors at the input circuit will enhance the surge capability and protect the lifetime of the LED light. For industrial applications, relay coils are commonly used for valve switching for fluid/gas control. LV UltraMOV Varistor Application Examples (continued) When the relay switches, the relay coil attempts to maintain current flow, causing temporary high voltage spikes. The use of an LV UltraMOV Varistor in parallel with the relay switch would extend the life of the relay and reduce arcing during switching of the relay contacts. The UltraMOV varistor will absorb the arcing energy from the energy released from the magnetic fields of the relay. 11

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