The working principle of a discharge tube is gas gap discharge. When a certain voltage is applied between the two poles of the discharge tube, an uneven electric field is generated between the poles. Under the action of this electric field, the gas inside the tube begins to escape. When the applied voltage increases to the extent that the field strength between the electrodes exceeds the insulation strength of the gas, the gap between the two electrodes will be discharged and broken down, changing from the original insulating state to a conductive state. After conduction, the voltage between the two electrodes of the discharge tube is maintained at the residual voltage level determined by the discharge arc path, which is generally very low. This enables electronic devices connected in parallel with the discharge tube to be protected from damage caused by overvoltage.