Detailed Explanation of the Working Principle and Use of Varistor

When the varistor is working, each varistor unit is subjected to surge energy, and these varistor units are generally evenly distributed in the entire resistor body, that is, the entire resistor body is subjected to energy, rather than only the Zener diode regulator. The junction area withstands electrical power, which is why ceramic varistors have much larger current and energy ratings than Zener diode regulators. Its resistance value varies with the terminal voltage.

When the voltage applied across the varistor is lower than the nominal rated voltage, the resistance value is close to infinity, and there is little current flow inside. When the voltage across 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 a high resistance state; when the voltage exceeds its maximum limit voltage, the voltage is completely broken down and cannot be recovered.

The main features of varistors are wide operating voltage range (6-3000 volts, divided into several grades), fast response to overvoltage pulses (several to tens of nanoseconds), and strong impulse current resistance (up to 100-20 kA) , Small leakage current (less than a few to tens of microamps), small temperature coefficient of resistance, excellent performance, low price and small size. It is an ideal protective element. It can be composed of overvoltage protection circuit, noise elimination circuit, spark elimination circuit and absorption circuit.

What is the use of a varistor? Its major feature is that when the voltage applied to it is lower than its threshold 'UN', the current flowing through it is extremely 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, abnormal overvoltages that often occur in circuits can be suppressed, and circuits can be protected from overvoltages. The voltage placed on it is lower than the critical value, the valve is opened by the current, causing the suppression circuit to generate a special voltage, thus protecting the circuit from the danger of overvoltage.

A varistor is a component with transient voltage suppression and can be used to replace a combination of TVS diodes, Zener diodes, and capacitors. Varistors protect integrated circuits and other devices from damage from electrostatic discharge, surges, and other transient currents such as lightning strikes. When using, just connect the varistor in parallel with the protected IC or device circuit. When the voltage is momentarily higher than a certain value, the resistance of the varistor drops rapidly, conducting a large current, thereby protecting 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 an open circuit, so it will not affect the normal operation of the device or electrical equipment.

However, it should be noted that 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.