Damage discrimination and failure mode analysis of varistor

Date：2022-01-17 14:20:02Views：1490

Varistor is a voltage limiting protection device. Using the nonlinear characteristics of varistor, when overvoltage occurs at its two poles, varistor can clamp the voltage to a relatively fixed voltage value, so as to protect the subsequent circuit. Varistors also play a very important role in transient overvoltage protection in circuits. Although its flow capacity is large, its energy capacity is not large. In addition, because its impulse current pulse width is far less than the actual pulse current width of large and medium-sized power semiconductor systems, short circuit, burnout and failure often occur.

The failure mode of varistor is mainly short circuit. However, short circuit will not cause damage to varistor, because the resistance is at the positive and negative inlet of power supply; The insurance is good, which proves that it is not caused by short circuit or overcurrent. It may be that the surge energy is too large and exceeds the absorbed power to burn the varistor; When the overcurrent is too large, it may also cause the valve plate to be cracked and open circuit.

There are three failure modes of varistors:

The first deterioration,As the leakage current increases, the varistor voltage decreases significantly until it is zero.

The second burst,If the surge energy caused by overvoltage is too large and exceeds the bearing capacity of the selected varistor limit, ceramic cracking will occur when the varistor suppresses overvoltage.

The third perforation,If the overvoltage peak value is particularly high, most of the failure modes of the varistor appear as deterioration of each perforation (short circuit). The solution is to connect a suitable circuit breaker or fuse with the varistor in series to avoid accidents caused by short circuit.

Varistors also play a very important role. Varistors are mainly used for transient overvoltage protection in circuits. However, although its current capacity is large, its energy capacity is not large. In addition, its impulse current is large, and the pulse width is far less than the actual pulse current width of large rate semiconductor system. Therefore, short circuit, burn out and failure often occur.

How to judge the damage of varistor? Share the following methods:

Method 1 for distinguishing and testing varistors:

It is necessary to know the voltage value of the varistor first. A suitable voltage source can be connected in series with a protective resistor to apply voltage to the varistor. Measure the voltage value of the varistor to see whether it is on the nominal value. If so, it can be considered that the element is good. If there is a large deviation from the nominal value, there is a problem with the varistor.

Method 2 for distinguishing and testing varistors:

Varistors are generally used in parallel in the circuit. When the voltage at both ends of the resistor changes and exceeds the rated value, the internal resistance of the resistor decreases sharply and presents a short-circuit state. The current fuse connected in series on the circuit is blown to play a protective role. Varistors are often used in power overvoltage protection and voltage stabilization in circuits. With the three parameter tester of varistor, the voltage, leakage current and @ linear coefficient of varistor can be measured. In the case of part-time work, set the multimeter at 10K and connect the probe to both ends of the resistance. The resistance value marked on the varistor shall be displayed on the multimeter. If the deviation from this value is very large, it indicates that the varistor has been damaged.

Method 3 for distinguishing and testing varistors:

We all know that any electronic original itself stores capacitance. According to this principle, we can measure it with the capacitance of a digital multimeter. Capacity is good, otherwise the circuit is broken! Of course, the storage capacity of varistors with different models and parameters is also different.

The above is the related content of "varistor failure analysis" brought by the core detection. Through this paper, I hope it can be helpful to you. If you like this article, you might as well continue to pay attention to our website, and we will bring more wonderful content later. If you have any needs related to the inspection and testing of electronic products, please call Chuangxin testing, and we will serve you wholeheartedly.