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          GDT principle
          Publish:Shenzhen Tergy Technology Co., Ltd.  Time:2016-10-31
          Ceramic gas discharge tube is a switch type protection device, the working principle of gas discharge. When the voltage between the two poles is large enough, the pole gap will be put into electrical breakdown, which is transformed from the original insulating state into a conductive state, similar to a short circuit. The voltage between the two poles is very low, generally in 20 ~ 50V, so it can protect the effect of the circuit. The main parameters of the ceramic gas discharge tube: response time, DC breakdown voltage, impulse breakdown voltage, flow capacity, insulation resistance, interelectrode capacitance, freewheeling trip time.
          The response time of the ceramic gas discharge tube can reach hundreds of NS and MS, the protective device is the most slow. When the cable on the lightning overvoltage of the tube short circuit breakdown ceramic gas discharge lightning protection device when the breakdown voltage of the initial basic ceramic gas discharge tube impulse breakdown voltage, the discharge tube breakdown conduction between the sustain voltage drop to 20 ~ 50V; on the other hand, the flow through the gas discharge tube than the varistor ceramic resistance and TVS tube to large ceramic gas discharge tube and protection devices such as TVS combination should make the most of the current through the GDT discharge, so the ceramic gas discharge tube is generally used for the front level protection circuit, then the level of protection circuit varistor or TVS tube, the response time of the two the device is very fast, a better protection effect on secondary circuit.
          The response time of the actual figure ceramic gas discharge tube
          Ceramic gas discharge tube insulation resistance is very high, can reach the magnitude of begohm. The value of the pole capacitance is very small, generally below 2pF, the very small leakage current is nA. The ceramic gas discharge tube and connected to the line on the line will not constitute what effect.
          GDT freewheeling trip is a key factor for the circuit design problem. As mentioned earlier, ceramic gas discharge tube continuous flow to maintain the voltage in 20 ~ 50V in the conductive state, used in the DC power supply circuit, if the two line voltage of more than 15V, can not be directly used in the discharge line two. The use of 50Hz in AC power circuit, while AC voltage are zero, can realize continuous current interrupting ceramic gas discharge tube, but the ceramic gas discharge tube type device after several conductive after the breakdown of the current interrupting capacity will be greatly reduced, after long-term use in the zero flow circuit can not be achieved wheeling is a trip; if the current and voltage phase is not consistent, may also lead to continued flow not interrupting. Therefore, in the phase AC power circuit protection of ground wire, the zero line and the line between the phase of single gas discharge tubes are not appropriate, when the electrical equipment adopts single-phase power supply and can not guarantee that there is no phase and neutral application reversed the possibility, the midline to separate protective ground ceramic gas discharge tube is not right now, the use of ceramic gas discharge tube and varistor series. In the phase AC power circuit protection on the midline of the basic does not use ceramic gas discharge tube.
          Ceramic gas discharge tube in the design of lightning protection circuit
          The design of lightning protection circuit, should pay attention to the ceramic gas discharge tube DC breakdown voltage, impulse breakdown voltage, current capacity and other parameters selection. Set the discharge in the ordinary AC line pipe, it can not be in the range of requirements of the normal operation of the line voltage and to allow the action, then it should meet the DC discharge voltage: min (ufdc) = 1.8UP. Ufdc (ufdc), (min) indicates the minimum value of DC breakdown voltage. UP is the peak of the normal operating voltage of the circuit.
          Ceramic gas discharge tube can be mainly used in AC power line, line of mouth protection; protection and protection of the RTN between the DC signal line on the export; protection; protection of feeder line on the antenna port core shielding layer.
          Ceramic gas discharge tube failure mode in most cases is open, due to circuit design reasons or other factors of discharge tube in a short-circuit state for a long time and burn, can also cause the short circuit failure mode.
          LangTuo-GDT ceramic gas discharge tube with surge protection of high level, with a variety of voltage, low capacitance and a variety of shapes including new surface mount devices for MDF (MDF) module, high-speed data telecommunications (e.g. ADSL, VDSL), and the power line surge protection applications.
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