Over-voltage transients often occur in electric circuit. Such abnormal voltages are often caused by lightning strikes,atmospheric lightning discharges,accidental contact between power and communications lines,unexpected rise in the supply voltages of the installation as a result of misoperation,and appearance of voltage higher than normal during switching operations.The over-voltage transients,if not properly taken care of, not only cause damage to delicate components such as semiconductors,ICs and others in the equipment,but also are highly dangerous to personnel.Thus,protection against over voltages is necessary for high reliability and long life of general electronic equipment.The better protection selection for the over-voltage transients is ceramic gas discharge tubes.

The Ceramic gas discharge tube is a switching component which is controlled by voltage.It is used to be parallel connected between the line and line of equipment,or between the line and the ground(show as the bottom figures).If the over-voltage doesn't reach GDT's action voltage,the ceramic gas discharge tube will be in high resistance status.If the over-voltage is higher than GDT's action voltage,the GDT's internal gap will then break down.The Ceramic gas discharge tube is almost short-circuit at this time and limits the over-voltage to almost 0 volt within 50ns,so the surge current can be led to ground rapidly and then the equipment can be protected safely.When the over-voltage disappears, the Ceramic gas discharge tube will extinguish and return to high insulation status,preparing for the next action.