Regarding the working principle and function of the gas discharge tube, the working principle of the gas discharge tube can be simply summarized as the gas discharge, the suppression circuit composed of the gas discharge tube and the varistor, and the role of the gas discharge tube in the comprehensive surge protection system.
How gas discharge tubes work
First, the working principle of gas discharge tube
The ceramic discharge tube is sealed with ceramics, and the interior is composed of two or more metal electrodes with gaps, which are filled with inert gases argon and neon.
The working principle of gas discharge tubes can be simply summarized as gas discharge. When a sufficient amount of electricity is generated between the two stages, the gap between the electrodes will be broken down by discharge, and then it will change from an insulating state to a conductive state, which is similar to a short circuit.
When it is in a conductive state, the voltage between the two poles will be low, generally between 20 and 50V, so it can play a good role in protecting the subsequent circuit.
The gas discharge tube is sealed in a ceramic package, and the interior is composed of two or more metal electrodes with gaps filled with inert gas (argon or neon). Gu also has engineers who call it a ceramic discharge tube and a ceramic gas discharge tube. When the voltage applied to the two electrode terminals reaches the breakdown of the gas in the gas discharge tube, the gas discharge tube starts to discharge and changes from high resistance to low resistance, so that the voltage across the electrodes does not exceed the breakdown voltage.
1. The role of gas discharge tubes in various communication equipment such as telephones/fax machines
Features are low current, high continuous power supply, no leakage current, and high reliability.
2. Suppression circuit composed of gas discharge tube and varistor
Because the varistor has a fatal disadvantage: it has an unstable leakage current, and after a varistor with poor performance is used for a period of time, it may heat up and explode due to the increase of the leakage current.
To solve this problem, a gas discharge tube is connected in series between the varistors. But this also brings the disadvantage that the reaction time is the sum of the reaction times of each device. For example, the response time of the varistor is 25ns, and the response time of the gas discharge tube is 100ns, then the response time of R2, G, R3 in Figure 4 is 150ns, and the R1 varistor is added to improve the response time, so that the response time can be 25ns .
2. The role of gas discharge tube in integrated surge protection system
The surge protection system required by the automatic control system is generally composed of two or three levels. Reliable protection can be achieved by utilizing the characteristics of various surge suppression devices. The gas discharge tube is generally placed at the input end of the line as a primary surge protection device to withstand large surge currents.
The secondary protection device uses a varistor for faster response in the μs time scale. For highly sensitive electronic circuits, a three-level protection device TVS can be used to respond to surge voltages within a ps-level time range.
When a surge such as lightning arrives, the TVS will start first, which will accurately control the instantaneous overvoltage to a certain level; if the surge current is large, the varistor will start and discharge a certain surge current; the voltage at both ends will have It is increased until the discharge of the gas discharge tube of the front stage is pushed, and the large current is discharged to the ground.
Summary: The role of the gas discharge tube is that the gas discharge tube almost perfectly meets all the requirements of a protective element. It can reliably limit the overvoltage within the allowable value range, and under normal operating conditions, due to the high insulation resistance and low capacitance characteristics, the discharge tube does not actually have any effect on the protected system.