The role of varistor

Tell you about the function of the varistor

Detailed explanation of the use of the varistor

I.The principle of the varistor

The varistor means "within a certain range of current and voltage, the resistance value changes with voltage", or "the resistance value is sensitive to voltage"

With the increase of the voltage applied to it, its resistance value can change from M (megohm) to M (milliohm) When the voltage is low, the varistor works in the leakage current region, which is characterized by high resistance and low leakage current. When the voltage rises to the nonlinear region and the current changes in a large range, the voltage changes very little, which shows good voltage limiting characteristics. When the voltage rises again, the varistor enters the saturation region, which shows a small linear resistance. Due to the high current, the varistor will overheat, burn or even burst over time, During normal use, the varistor is in the leakage current region. When it is impacted by the surge, it enters the nonlinear region to release the surge current, but generally cannot enter the saturation region

II. The function of the varistor

The characteristic of the varistoris that when the voltage applied on it is lower than its threshold value 'UN', the current flowing through it is very small, which is equivalent to a closed valve. When the voltage exceeds UN, the current flowing through it surges sharply, which is equivalent to the opening of the valve. With this function, the abnormal overvoltage that often occurs in the circuit can be suppressed, In addition, it can protect the circuit from the impact of overvoltage.

The varistor is a component with transient voltage suppression function, which can be used to replace the combination of transient suppression diode, zener diode and capacitor. The rheostat can protect the integrated circuit and other devices from the damage of electrostatic discharge, surge and other transient current (such as lightning strike). When used, it is only necessary to connect the rheostat in parallel on the protected IC or equipment circuit, When the voltage is instantaneously higher than a certain value, the resistance of the varistor will drop rapidly and conduct large current to protect the IC or electrical equipment; When the voltage is lower than the working voltage of the varistor, the resistance of the varistor is extremely high, almost open circuit, so it will not affect the normal operation of the device or electrical equipment

III. Use of rheostats

Rheostats are usually used in parallel circuits. When the voltage at both ends of the resistance changes sharply, the short circuit of the resistance will burn the current fuse and play a protective role. Rheostats are often used for power overvoltage protection and voltage stability in circuits

The reliability and safety of power lightning arrester largely depends on the correct use ofvaristor. The following principles can be used as a reference, especially in the lightning protection design of power supply, the differences in power quality, lightning frequency and intensity, installation and use of protected equipment, impact resistance and other aspects should also be considered, and the same formula cannot be copied, The designed lightning protection device must be tested and verified under the site use conditions or simulation conditions as close as possible to the real situation

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