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How do I choose a thin film capacitor? What's the point?

Views:2     Author:Site Editor     Publish Time: 2021-04-02      Origin:Site

1. The rated voltage of the capacitor:

Refers to the peak of the DC voltage or pulse voltage that can be continuously applied to the capacitor over a rated temperature range. Due to the reliability devolved usage requirements, the actual operating voltage is usually required to be less than 80% of the rated voltage.

 

2. The operating voltage selection of the capacitor:

Through the pulse voltage and voltage resistance of the capacitor, due to the loss of the thin film capacitor, when used at high frequencies and high pulse conditions, if there is a large current through the capacitor will cause the film capacitor's own heat, in severe cases there will be a risk of thermal knock-through (smoke, knock-through), so the use is also limited by the capacitor rated current. When using, it is important to ensure that both voltages are within the allowable range. If the actual operating voltage (current) waveform cannot be determined, it can be determined by the self-temperature rise of the capacitor working, usually for polyester capacitors, allowing the self-temperature rise to be used under conditions less than 10C. For polypropylene capacitors, it is allowed to be used at a temperature rise of less than 5 degrees C. (Actual measurements should be tested on the surface of the lead welding site at the end of the capacitor)

 

3. Capacitor capacity and lead span selection:

1) Capacity selection must be within 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 for a total of 24 levels, where the horizontal line below is the E12 series value, which is the preferred series.

 

2) The capacity range shall conform to the capacity range given in the general specifications of all types of capacitors:

Specifications provided by different manufacturers, its capacity of the upper and lower limit range may be slightly different, but if the capacity selection value has been significantly lower than the lower limit of the category, it should be selected in the ceramic capacitor, and the other is if the capacity value is higher than the upper limit of the category, it should be selected in the electrolyte capacitor.

 

3) Selection of lead molding foot pitch:

Different models of different specifications of thin film capacitors, its lead conventional spacing P in the manufacturer's specifications have a definite value, but in practice, according to the PCB assembly requirements, manufacturers can be required to mold supply, given the size requirements of the molding foot distance F. However, because the user does not consider the actual value of the capacitor's natural foot distance P, freely formulate the forming foot distance F value, resulting in the existence of many unreasonable molding dimensions, that is, affecting the process assembly effect, but also to the supplier supply caused great difficulties, must cause the user's attention, and require the molded foot distance F should be as close to the capacitor as possible conventional foot distance P, and must follow the following molding standards:

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

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

 

In summary, the selection of thin film containers must be based on a full understanding of the characteristic parameters of various types of capacitors and can determine the working conditions of the line in order to achieve the correct selection, but also must take into account the principle of standardized generalization.


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