In today's highly electronic world, the role of varistor cannot be underestimated. It is a resistor based on semiconductor materials (mainly zinc oxide) and plays the role of gatekeeper for circuit protection. The core functions of varistor can be summarized into three categories: one is over-voltage protection, the other is to meet the requirements of lightning resistance, and the third is to meet the needs of safety testing. Different from traditional sensors, varistor is a voltage sensor, and its working principle is similar to that of a fuse, that is, once the voltage limit it withstands is exceeded, breakdown will occur, thus disconnecting the circuit and playing a protective role.
Although varistor is widely used in overvoltage protection equipment and has a large current capacity, its energy capacity is limited. More specifically, its width adaptability to inrush current pulses is much smaller than the actual pulse current widths encountered in large and medium-power semiconductor systems. This characteristic causes the varistor to easily short-circuit or even burn out when faced with extreme voltage shocks.
Analysis of the specific reasons for the burnt varistor:
Aging failure: As time goes by, the resistance of the varistor will gradually decrease, resulting in a vicious increase in leakage current. During this process, the current concentrates on the weak point, causing the material to melt, and eventually a short-circuit hole is formed, which in turn causes the current driven by the power supply to pass through the short-circuit point, generating high heat and causing a fire. To prevent such an event, a thermal junction is usually connected in series between the varistor and the circuit.
Transient overvoltage: When faced with a strong transient overvoltage, the resistor body of the varistor may be perforated, causing a large current to pass through, thereby generating high heat and causing a fire. This damage occurs so quickly that the hot melt joint cannot respond in time and melts, making it impossible to effectively avoid damage.
Factors such as the number of overvoltage protections, working environment temperature, mechanical pressure, quality certification, excessive surge energy, insufficient voltage resistance, excessive current and surge are also common causes of varistor burnout. These factors may interact to contribute to the eventual burnout event.
The safety of use of varistor is an issue that cannot be ignored. In view of its wide application in household appliances and other electronic products - it plays multiple roles such as over-voltage protection, lightning protection, surge current suppression, spike pulse absorption, amplitude limiting, high-voltage arc extinguishing, noise elimination, and protection of semiconductor components. , it is crucial to choose high-quality varistors. This is not only related to the stable operation of the circuit, but also related to the safety of the equipment and users.
When selecting a varistor, in addition to considering its basic electrical performance, it is also necessary to comprehensively consider the use environment, expected electrical impact intensity and other factors to ensure that it can not only meet the needs of circuit protection, but also effectively avoid the risk of damage caused by the varistor itself. safety accidents caused by defects. Therefore, the selection, use and maintenance of varistors must follow strict standards and specifications to ensure the stable and safe operation of electronic equipment.