● Introduction 
    Varistors produced by our company are mainly used to adsorb transient overvoltage such as switching overvoltage and lightning overvoltage, to prevent such overvoltage interfering with the normal operation of circuit, and to protect all components in the circuit from being damaged.

Features:
Wide voltage range of varistors （18V-1800V） Nonpolar
Quick response (millisecond )                          High withstanding surge current
Large nonlinear coefficient                                        Reliable operation

·Selection methods of varistor:    
  For varistors used for overvoltage protection, the varistor voltage can be selected according to the following formula: 
                V1mA=a.V/b.c
where:
    a  Fluctuation coefficient of power voltage, generally taken 1.2~1.4      
    b  Varistor voltage error, generally taken 0.85~0.80
    v  AC working voltage (taken peak value)             
    c-Aging coefficient of components, generally taken 0.9

·Selection of withstanding surge current, and derating features of varistors:
   The withstanding surge current indicated in this contents is the maximum current that product can withstand during the impact test, carried out with the specified waveform, amplitude and interval time in accordance with the product standard (after test, the product V1mA rate of change is ≤10%). With change of waveform, amplitude and internal time, the impact frequency will also change. 

                  

The derating characteristic line of Ip is as follows: 

                  

    Withstanding surge current in the specimen copy is the maximum current value that varistor can withstand after impacted once or twice by 8/20μS current wave. When time width T or impact frequency n of current wave increases, the allowable peak current reduces.
    Five index values of varistors as the maximum continuous working voltage (UAC, UDC), maximum impact current Im, rated power Pm and rated energy Em are those when the ambient temperature is lower than 85℃. When the ambient temperature is above 85℃, the values shall be determined according to the following derating curve. 

                  

·Voltage characteristic and application principle of varistor:
    The basic feature of varistor is the corresponding relationship between the current passing through varistor and the voltage at the two ends of components, i.e., the voltage current characteristic curve of varistor. 

              

    When the voltage at the two ends of varistor is lower than threshold voltage (varistor voltage), its resistance can be very large (up to megohm), and the current is very low. When the voltage at the two ends is larger than the varistor voltage, the resistance decreases rapidly (low to the ohm), and the current is very large. This characteristic makes the varistor be able to adsorb switching overvoltage and lightning overvoltage, so as to protect the line from being damaged.