Principle applications of zinc oxide varistors

Varistor(Metal Oxide Varistor) is the purpose of a Promise of overvoltage protection elements, either AC or DC circuits, simply varistor and the protected electrical equipment or components in parallel to achieve protection equipment (Figure 4 shows )

When the overvoltage magnitude higher than the provisions of the current-voltage, over current amplitude is less than the maximum peak current of the varistor (If there is no The varistors sufficient destruction of the equipment components), the varistor is in breakdown instantaneous voltage areas can be too limited to a very low amplitude, this time through the varistor surge current amplitude (<100A/cm2) insufficient to produce deterioration varistor; had been the amplitude of the voltage is high, the over-voltage of the varistor is limited at a lower level (less than the voltage level of the device), while through the varistor inrush current is large, so that deterioration of the performance of the varistor Nearing, when the current through the fuse, fuse disconnect electrical equipment so that it can enable the components from voltage surges, it can also avoid breakdown caused by the deterioration of the varistor line LN, L between-PE short circuit (Recommended fuse sizes are shown in Table 1).

Varistor in the over-voltage protection of the circuit, if the normal work in the pre-breakdown region and the breakdown region of the Figure 3, in theory, is not damaged. But because of the varistor long withstand the power supply voltage, circuit transient over-voltage, ultra-energy over-voltage random impact and release energy absorption circuit energy storage element, therefore, the varistor is damaged, its lifespan varies according to where the circuit is subjected to over-voltage amplitude and different energy.

Application Type

Use of different occasions, the application purpose of the varistor(Metal Oxide Varistor), the varistor voltage / current stress is not the same, and thus the requirements of the varistor is not the same, note the distinction between this difference is very important, for the proper use of 's.

Depending on the intended use, the varistor area is divided into two categories: ① protection varistor ② circuit functions Varistors for use.

Protection with varistor

(1) distinguish between power protection with the signal line, a data line protection varistors, they are to meet the requirements of different technical standards.

(2) depending on the continuous operating voltage applied to the varistor, the cross-power line varistors District is divided into exchanges with or DC with two types of varistors in both voltage stress performance of different aging characteristics.

(3) According to the varistor withstand abnormal over-voltage characteristics of different, may be the pressure-sensitive resistor region into surge suppression, high-power and high energy type of these three types.

★ surge suppression: for to suppress lightning over-voltage and operating voltage, etc. transient over voltage varistor, this transient over voltage appear random, non-periodic, current and voltage peak may large. The vast majority of the varistor fall into this category.

★ high power type: varistor continuous burst for the absorption cycle, such as varistors and connected to the switch on the power converter, impulse voltage cycle, and the cycle we can see, the energy value generally can calculated, and the peak of the voltage is not large, but the high frequency of appearance, its average power is quite large.

★ high-energy type: the type of application, the main technical indicators is the energy absorption capacity for the absorption of the the generator excitation coil, lifting large solenoid coil inductance coil magnetic energy varistor voltage.

Varistor protection function, the vast majority of applications, can be repeated role, but sometimes it is made as a "one-time" protection current fuse devices. For example, and then some current transformer load with short circuit contact varistor(Metal Oxide Varistor).

Varistor circuit functions

The varistors are mainly used in transient overvoltage protection, but it's similar to the semiconductor zener voltage characteristics, and also it has a variety of circuit elements, for example, can be used as:

(1) DC high voltage current regulator components, its stable voltage can be as high as several thousand volts, this can not be achieved by silicon regulator.

(2) The voltage fluctuation detection element.

(3) DC bottle displacing element.

(4) of the equalizing element.

(5) Fluorescent actuation element (Metal Oxide Varistor)