Transient overvoltages often occur in electronic circuits. The causes of the abnormal overvoltage include lightning strike, accidental contact between the power line and the communication line, accidental increase of the supply voltage of the device due to misoperation, and surge voltage during the switch operation. If not handled in a timely manner, transient overvoltage may not only damage semiconductors, integrated circuits, and precision components inside the device, but also pose a threat to personal safety. Therefore, if the electrical equipment to have high reliability and long life, it must be effective protection against overvoltage. It is better to choose gas discharge tube to prevent transient overvoltage effectively.

The discharge tube is a voltage conductive switching device, which is connected in parallel between the line and the line of the protected equipment or between the line and the ground (as shown below). When foreign surge voltage of the actuating voltage, discharge tube with high resistance (more than 1000 m Ω) insulation resistance state, and once the surge voltage reaches its action voltage, discharge tube internal electric breakdown occur immediately discharge gap, the discharge tube is equivalent to a good conductor, the surge voltage in the 50 ns time is short circuit to nearly zero voltage quickly, The surge current is quickly introduced into the ground, thus protecting the equipment. When the surge voltage disappears, the discharge tube will immediately extinguish and return to the high resistance state, waiting for the next action.