Views: 4 Author: Site Editor Publish Time: 2019-08-07 Origin: Site
The varistor is equivalent to a variable resistor. It is connected in parallel with the circuit. When the circuit is in normal use, the varistor has a high impedance, and the leakage current is small. It can be regarded as an open circuit and has little effect on the circuit. But when a very high surge voltage comes, the resistance value of the varistor drops instantaneously. Its resistance value can be changed from megaohm to milliohm, so that it can flow a large current while clamping the overvoltage. Bit is at a certain value.
Since the surge resistance of the varistor depends on its physical size, it is possible to obtain different inrush current values. The characteristic of a varistor is that when the voltage applied to it is lower than its threshold "UN", the current flowing through it is extremely small, equivalent to a shut-off valve. When the voltage exceeds UN, its resistance becomes small, so that the current flowing through it surges and the influence on other circuits does not change much, thereby reducing the influence of overvoltage on subsequent circuits.
With this function, it is possible to suppress abnormal overvoltages that often occur in circuits and protect circuits from overvoltages. The varistor is a voltage-limiting protection device that utilizes the non-linear characteristic of a varistor. When an overvoltage occurs between the two poles of the varistor, the voltage can be clamped to a relatively fixed voltage value, thereby realizing the latter stage circuit. protection of.
When a varistor does not meet the requirements of the nominal discharge current, multiple varistor should be used in parallel. Sometimes in order to lower the limit voltage, multiple varistors are used in parallel even if the nominal discharge current meets the requirements. It is important to note that when the varistor is used in parallel, it is necessary to strictly select the parameters for matching to ensure uniform distribution of current.
