What is the varistor?

1.Properties

The varistor is a special resistor made of the nonlinear characteristics of the semiconductor material. When the voltage applied at both ends of the varistor reaches a critical value ( varistor voltage ), the resistance of the varistor will be reduced dramatically.

When the applied voltage at both ends is within the nominal rating, the resistance is almost infinite, in a high resistance state, and the leakage current is 50mA; when the voltage at both ends is slightly above the rated voltage, the value of the resistance drops sharply, immediately in the conduction state, and the reaction time is only nanosecond level, the operating current increases rapidly, thus effectively protecting the circuit.

2.The main parameters of the varistor

The main parameters of the varistor are nominal voltage, leakage current and flux.

( 1 ) Nominal voltage ( VxmA )

Nominal voltage, also known as varistor voltage, refers to the voltage across the varistor at 1 mA DC current.

( 2 ) Leakage current

When the voltage at both ends of the element is equal to 75 % VxmA, the DC current on the varistor.

( 3 ) Pass traffic within the specified time ( 8 / 20 s ), allowing the maximum value of the pulse current.

3.Detection

( 1 ) Good or bad measurement

Uses the highest gear ( 10K block ) of the electric barrier of the pointer multimeter, and the resistance value of the two pins of the varistor should be infinite at room temperature, using the digital table, the display will display the overflow symbol " 1 ".

 If there is a resistance, it is shown that the breakdown voltage of the varistor is lower than the 9V (or 15V) voltage of the battery in the multimeter (this is rare), or is damaged by the breakdown

(2).The nominal voltage measurement  is used to detect the varistor circuit D. If the IGRAM needs to measure its rated voltage (breakdown voltage), it can be connected to an adjustable power supply and a series of human ammeters to adjust the adjustable power supply. At the beginning, the ammeter is basically the same; when the EC rises again, the ammeter's meter is swung, and the voltage at both ends of the rheostat is measured by a multimeter (nominal voltage). The adjustable power supply can be replaced by a MEM table.

4.The using of varistor in the actual circuit

In the actual circuit, the varistor can be used in parallel and in series.

Parallel usage can increase the value of surge current, but requires the same nominal voltage of the parallel device. Series usage can increase the nominal voltage value that is actually used, and the nominal voltage value after series is usually the sum of two nominal voltage values. When the varistor is selected, the lower the nominal voltage is chosen, the higher the protection sensitivity, but the nominal voltage is too low, and the current flowing through the varistor is also corresponding larger, will cause the varistor own loss increases and fever, easy to burn the varistor. In practical applications, it is determined that the nominal voltage can be 1.73 times the working circuit voltage to approximate the nominal voltage of the varistor.

This article is from Allicdata Electronics.