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The use principle of Varistor is that after it is connected to the protected equipment, it cannot affect the normal operation of the equipment, and can effectively implement instantaneous overvoltage protection for the equipment. Therefore, in addition to the technical parameters of Varistor, the following issues should be considered in the actual selection:

(1) Selection of voltage sensitivity
Considering the deviation between the actual Varistor voltage and the nominal voltage (1.1~1.2 times of the nominal voltage should be considered), the possible fluctuation range of the power supply voltage in the AC circuit (1.4~1.5 times of the rated voltage should be considered), and the relationship between the peak value of the AC voltage and the effective value (1.4 times should be considered), the Varistor with a voltage sensitive of 2.2~2.5 times of the rated voltage should be selected. In DC circuits, Varistor with a voltage sensitive of 1.8~2 times the rated value of DC voltage are often selected.

⑵ Selection of flow capacity
In principle, the selection should be based on the maximum transient surge current that may be experienced, but achieving this is difficult. In practice, the selection of Varistor is based on the use occasion or the test grade specified in the product test standard.

According to the former, 1kA (8/20 μ S current wave) can be used for the protection of silicon controlled rectifier; 3kA is used for surge absorption in electrical equipment; 5kA is used for overvoltage absorption of lightning strikes and electronic equipment; 10kA is used for protection against lightning strikes. According to the latter, the commonly used composite wave (1.2/50 generated when the generator is open circuit output) μ Voltage wave of s; 8/20 generated during short-circuit output μ Current wave of s; The internal resistance of the generator is 2 Ω to assess the equipment's ability to withstand lightning surge interference online. During the 4kV test, the maximum current absorbed by the protector can reach 2kA; For the 6kV test, the maximum absorbed current is 3kA. However, in actual selection, the flow capacity of the selected Varistor should also be appropriately increased. Because Varistor with large current passing capacity should have relatively small residual voltage drop when absorbing surge current of the same size; At the same time, there is also a large protection margin for the selected Varistor.

⑶ Inherent parasitic capacitance
Varistor has an inherent capacitance problem. Its value ranges from hundreds to thousands of pF according to the difference of external dimensions and nominal voltage. The inherent capacitance of Varistor determines that it is not suitable for use in high-frequency occasions, or it will affect the normal operation of the system; Suitable for use in power frequency systems, such as for protection of power incoming lines, protection of thyristor rectifiers, etc.

The instantaneous power of Varistor is relatively large, but the average continuous power is very small, so it cannot work in the conduction state for a long time.https://www.kingtronics.com/Metal-Oxide-Varistor/XKT-Metal-Oxide-Varistor.html 

Kingtronics Kt 05D to 20D Metal Oxide Varistor Features
Operating Temperature Range: -40℃~+105℃
Body Diameters Range From 5D to 20D
Wide Operating Voltage from 18V to 1800V
Full compliance with RoHS and REACH

Kingtronics Kt 05D to 20D Metal Oxide Varistor Applications
Industrial equipment
Home appliance
Industrial equipment
Lighting products
Telecommunication or telephone system

Following our Precision Potentiometer RKT-3540S & RKT-3590S now have much better prices with competitive quality than before, welcome your inquiry.

RKT-3540S Precision Potentiometer (Multiturn) -102/202/502/103/203/503
RKT-3590S Precision Potentiometer (Multiturn) -102/202/502/103/203/503

Product video-Kingtronics supply PCB mount trimmer potentiometers , intended for infrequent adjustment
https://www.youtube.com/watch?v=QmobgUHYBus&list=UULFr_Oi3-4vXEHq8INdSANldQ&index=11

Kingtronics produce Potentiometer professionally for about 30+ years with ISO & SGS Certified. Following our Precision Potentiometer with competitive quality and price, welcome your inquiry.

RKT-3540S Precision Potentiometer (Multiturn) -102/202/502/103/203/503
RKT-3590S Precision Potentiometer (Multiturn) -102/202/502/103/203/503

**Features:
Bushing mount precision potentiometer
Metal shaft and bushing
Wirewound potentiometer
Multiturn potentiometer

Lead time: 4-7 weeks
Product video : https://www.youtube.com/watch?v=ZQiJx5bjvbk&t=3s

Trimming Potentiometers has always been one of the best seller in Kingtronics, we always possessed with great advantage in the global market.

Kingtronics offer verities type of trimming potentiometer, we maintain the stable lead time for only 4-6 weeks.

lplease refer to below partial products list. Welcome to contact us info@kingtronics.com for the further best quotation. 

Dear valued customer,

Are you looking for Precision Potentiometer RKT-3540 and RKT-3590 ?
Kingtronics could make replacement of Bourns with much more competitive prices and fast lead time

More values we can produce:

RKT-3006 3/4" (19 mm) Rectangular Trimming Potentiometer
RKT-3266 1/4" (6 mm) Square Trimming Potentiometer
RKT-3296 3/8" (9 mm) Square Trimming Potentiometer
RKT-3323 1/4" (6 mm) Square Trimming Potentiometer
RKT-3329 1/4" (6 mm) Round Trimming Potentiometer
RKT-3362 1/4" (6 mm) Square Trimming Potentiometer
RKT-3386 3/8" (9 mm) Square Trimming Potentiometer
RKT-3309 9 mm Through-Hole Cermet Consumer Trimming Potentiometer
RKT-3540S Precision Potentiometer (Multiturn)
RKT-3590 Precision Potentiometer (Multiturn)
RKT-C3305 Trimming Potentiometer-3mm SMD
RKT-065 Phenolic Consumer Trimming Potentiometer

Most people know BOURNS can produce 3540S, 3590 Multiturn Precision Potentiometer,but you also know they are with very high the price tag. Shrug !

Well, Kingtronics produce full range of trimming potentiometers under our company brand name " Kt" .
We are glad that 3540S, 3590 are our strong products among them with reasonable price and superior quality.
Free samples are on hand now, please contact with us for sample evaluation.

Click here to know more about our Trimming Potentiometers : 
www.kingtronics.com/trimming-potentiometers/
www.kingtronics.com/packing/trimming-potentiometers-packing.html