Detail the working principle and use of varistor

VaristorWhen working, each varistor unit bears surge energy, and these varistor units are generally uniformly distributed in the whole resistor body, that is, the whole resistor body bears energy, rather than only the junction area bears electric power like Zener diode regulator, This is also the reason why ceramic varistors have much larger current and energy ratings than Zener diode regulators. Its resistance varies with terminal voltage

When the voltage applied at both ends of the varistor is lower than the nominal rated voltage, the resistance value is close to infinity, and there is almost no current flow inside. When the voltage at both ends of the varistor is higher than the nominal rated voltage, the voltage quickly breaks through, from high resistance to low resistance, and the working current also increases sharply. When the voltage at both ends is lower than the nominal rated voltage, the varistor returns to the high resistance state; the voltage exceeds its maximum limit voltage The voltage is completely broken down and cannot be recovered

The main characteristics of the varistor are wide working voltage range (6-3000 V, divided into several grades), fast response to overvoltage pulse (several to tens of nanoseconds), strong impact resistance (up to 100-20 kA), small leakage current (less than several to tens of microamps), small resistance temperature coefficient, excellent performance, low price and small volume. It is an ideal protection element. It can be composed of overvoltage protection circuit, noise elimination circuit, spark elimination circuit and absorption circuit

VaristorWhat's the use of it? Its main feature is that when the voltage applied to it is lower than its threshold value 'UN', the current flowing through it is very small, equivalent to a closed valve. When the voltage exceeds UN, the current flowing through it surges sharply, which is equivalent to valve opening. With this function, the abnormal overvoltage that often occurs in the circuit can be suppressed and the circuit can be protected from overvoltage. The voltage placed on it is lower than the critical value, and the valve is opened by the current, which makes the suppression circuit generate special voltage, thus protecting the circuit from the danger of overvoltage

Varistoris a component with transient voltage suppression function, which can be used to replace the combination of transient suppression diode, Zener diode and capacitor. Rheostats can protect integrated circuits and other devices from electrostatic discharge, surge and other transient current (such as lightning) damage. When in use, it is only necessary to connect the rheostat in parallel to 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

However, due to the existence of leakage current, the leakage current index of the varistor is related to the normal operation of the protected electronic system, as well as the aging and service life of the varistor itself