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How to choose film capacitors? What are the precautions?

Views: 2     Author: Site Editor     Publish Time: 2021-08-21      Origin: Site

1.Rated voltage of capacitor:


Refers to the peak value of the DC voltage or pulse voltage that can be continuously applied to the capacitor within the rated temperature range. Taking into account the reliability and derating requirements, it is usually required that the actual working voltage should be less than 80% of the rated voltage value.


1. Selection of the working voltage of the capacitor:


Through the pulse voltage and withstand voltage of the capacitor,due to the loss of film capacitors, when used under high frequency and high pulse conditions, if there is a large current through the capacitor, the film capacitor will heat itself, and in severe cases, there will be a risk of thermal breakdown (smoke, breakdown), so the use of the capacitor is also limited by the rated current of the capacitor.When using, you must ensure that both voltages are within the allowable range.If the actual working voltage (current) waveform cannot be determined, the self-temperature rise of the capacitor can be used to determine it. Usually, for polyester capacitors, the self-temperature rise is allowed to be used under the condition of less than 10℃. For polypropylene capacitors, they are allowed to be used when their own temperature rise is less than 5℃. (The actual measurement should be tested on the surface of the lead welding part of the capacitor end surface).


2. Selection of capacitor capacity and lead span:

1)The capacity selection must meet the E24 series value range:1.0, 1.1, 1.2,1.3, 1.5,1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9,4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1,a total of 24 levels, among which the horizontal line below is the E12 series value, which is the preferred series value.


2)The capacity value range should conform to the capacity range given in the general specifications of various capacitors:

The upper and lower limits of the capacity of the specifications provided by different manufacturers may be slightly different,but if the selected value of the capacity has been significantly lower than the lower limit of the category, it should be selected from ceramic capacitors, on the contrary, if the value of the capacity has been higher than the upper limit of the category, it should be selected among the electrolytic capacitor.


3) Selection of lead forming pitch:

For film capacitors of different types and specifications, the conventional lead pitch P has a certain value in the manufacturer’s specifications, but in actual use, according to the PCB assembly requirements, the manufacturer can be required to form and supply, and the pitch F after the formation is given size requirements.But because the user does not consider the actual value of the natural pitch P of the capacitor, and arbitrarily sets the value of the forming pitch F, leading to the existence of many unreasonable forming dimensions, which affects the process assembly effect and causes great difficulties for the supplier. It must be highly valued by users, and the molding pitch F should be as close as possible to the conventional pitch P of the capacitor, and the following molding standards must be followed:


When P≥F, P-F≤8mm (F value is an integer multiple of 2.5);

When P《F, F-P≤5mm (F value is an integer multiple of 2.5).


In summary, the selection of film capacitors must be based on a full understanding of the characteristics of various capacitors and the ability to determine the working conditions of the line before they can be selected correctly. At the same time, the principles of standardization and generalization must be taken into account. Anhui Saifu Electronics specializes in manufacturing film capacitors, and more high-quality capacitors are available in Anhui Saifu.


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