Gas Discharge Tube Gdt Products Page 7 Gas Discharge Tube GDT Products

Gas Discharge Tubes 2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/12/17 through the device increases, the voltage which the MOV clamps at is greatly increased. MOV Voltage vs. Current Characteristics Current (A) Voltage (V) .001 1000 Leakage Region Upturn Region Clamping Voltage GDT and MOV PROTECTION: In summary, there is no one ideal surge arrester device type that meets all of the key performance parameters for every application. Due to their complementary performance characteristics, however, a GDT and MOV can be combined in a circuit to provide the ultimate in surge suppression performance. The MOV quickly clamps a fast rising voltage surge while the GDT crowbars to safely dissipate the large peak current to ground. (See Application Note entitled "Surge Protection of AC Power Lines".) SUMMARIZED COMPARISON OF TECHNOLOGIES GAS TUBE CG2-230L SCR MOV DIODE Type of Device Response Speed Capacitance Leakage Current Maximum Surge Current (8/20 sec wave form) CROWBAR <1 uSEC. 1pF MAX. <1 pAMP 20,000 AMPS CROWBAR <100nSEC. 50pF 50 nAMPS 500 AMPS CLAMP <100nSEC. 45pF 10,000 nAMPS 200 AMPS CLAMP <100nSEC. 50pF 10,000 nAMPS 50 AMPS Relative Cost $1.00 $1.50 $0.50 $1.50 The CLARE product engineering department provides objective technical expertise and application assistance to designer's of switching surge protection systems. Our mission is to assist you in designing the best solution to your specific application problem, regardless manufacturer. To access our team of engineering professionals call toll free 1-800 CPCLARE. CONSTRUCTION : Gas Discharge Tube (GDT) surge arresters commonly employ hermetically-sealed enclosures utilizing either ceramic-to-metal or glass-to-metal seals. The many advantages of ceramic-to-metal units have made them the norm for gas discharge tube surge arresters such as Littelfuse's GDTs. Along with being low cost, they offer high product uniformity capable of handling extreme levels of shock, vibration, and temperature. The ceramic for GDTs is alumina ranging from 94- 98% Al2O3. The ceramic-to-metal seals are prepared by moly- manganese or tungsten metallizing processes with nickel plating and the final seal is made in a gasfilled vacuum furnace using braze preforms made of copper-silver eutectic. The electrodes used for GDTs are either copper or a nickel- iron alloy, often with a coating to lower the work function and/or add gettering capability. Stripes or bands of semi- conductive material are applied to the inner surfaces of the ceramic to improve stability and high-speed response. In contrast, most devices in Littelfuse's High Energy Devices product line are glass-to-metal units. This allows greater flexibility in configuration and is ideal for the production of standard and custom parts in more limited quantities. The electrodes of High Energy Devices are usually made of refractory metals such as tungsten or molybdenum to meet more extreme life and surge capacity requirements. Gas Discharge Tube Typical Operating Characteristics Amps A A' B C D E F G V B Volts 10 -21 10 -15 10 -10 10 -6 10 -3 10 -1 1 10 100 Figure 1. A generic V-I characteristic of a plasma device. GDT Characteristics, Terms and Consideration Factors (continued)

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