Gas Discharge Tube Gdt Products Page 4 Gas Discharge Tube GDT Products

Gas Discharge Tubes 2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/12/17 Littelfuse gas discharge tube (GDT) surge arrester devices protect personnel and electrical equipment from damaging high voltage transients induced by lightning, inductive switching, or electrostatic discharge. Depending upon the application, Littelfuse offers a variety of two and three electrode GDTs for protecting telecommunication, test, computer, power supply, medical, and cable television equipment. Along with protecting circuits, GDTs can also be used as switches to create a discharge voltage in circuits used for medical, gas ignition, and HID lighting applications. Surge protectors protect personnel and equipment from damaging high-voltage surges from lightning, inductive switching, nuclear electromagnetic pulse, electrostatic discharge, or interference from power supply lines. From a design point of view, protection circuits only cost money and, if customer requirements or regulatory agencies do not require them, they will easily be forgotten. Yet, appropriate surge protection is beneficial. Protected equipment will not be affected by the highvoltage surges listed above. This will result in: Reduced field failures Improved product quality and reliability Reduced cost of quality The figure below illustrates the cost effectiveness of adding surge protection by demonstrating the unit repair cost to break even over a range of return rates for added protection costs of $0.50/unit and $1.00/unit. Cost Effectiveness Unit Repair Cost ($) Return Rate 0 50 100 150 200 250 300 350 400 450 2.0% 1.5% 1.0% 0.5% 0.0% $1.00 $0.50 Protection Cost/Unit (Breakeven) Through ongoing research and engineering improvements, Littelfuse has developed a family of Surge Protection Products that offer impressive characteristics for a variety of applications. Four differentiating characteristics are found in every Littelfuse Surge Protection Product: High surge current rating Long life Fast response Rugged construction In today's world of sensitive electronics, an increasingly important topic has become the protection of electronic components from overvoltage surges. There is a multitude of devices on the market for this purpose but what are the differences between them and which is best for what application? The following describes, analyzes, and compares these devices in detail. Basically there are two types of surge protection classifications with each consisting of its own group of devices: CROWBAR Air Gap Carbon Block Gas Discharge Tube (GDT) Silicon Controlled Rectifier (SCR) CLAMP Zener (Avalanche) Diode Metal Oxide Varistor (MOV) ------------------------------------------------------ CROWBAR PROTECTION: A crowbar device limits the energy delivered to the protected circuit by abruptly changing from a high impedance state to a low impedance state in response to an elevated voltage level. Having been subjected to a sufficient voltage level the crowbar begins to conduct. While conducting, the voltage across the crowbar remains quite low (typically less than 15 volts for gas discharge tubes usually higher for the air gap and carbon block protectors) and thus, the majority of the transient's power is dissipated in the circuit's resistive elements and not in the protected circuit nor the crowbar itself. This allows the crowbar to be able to withstand and protect loads from higher voltage and/or higher current levels for a greater duration of time than clamping devices. AIR GAP PROTECTOR: An air gap protector consists of two conductive surfaces with a spacing between them that will permit an arc when a specified potential is placed across the surfaces. The air gap is not a sealed device and therefore it must operate at atmospheric pressure and under the effects of the environment. Since the electrodes are exposed to the environment, they will often experience oxidation and corrosion which is not a problem common to a gas tube such as Littelfuse's GDT. These factors contribute to the air gap's high nominal breakdown voltage, wide breakdown voltage tolerance, and poor impulse response. Often an air gap is placed in parallel with a gas discharge tube or carbon block protector to provide back up protection in the event that the primary protection fails. Surge Arresters Why Use Surge Protection? A Comparison of Surge Arrester Technologies GDT Characteristics, Terms and Consideration Factors

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