Capacitor is generally made up of two close and mutually insulated conductors, is the foundation of military electronic machine is an indispensable component.
In military electronic products, electrolytic capacitor
has a considerable proportion of, its reliability plays an important role in the whole machine.
, according to the relevant domestic departments in the machine the cause of the problem, due to capacitor selection and application of fault about capacitor 55 ~ 85% of total failure rate;
Resulted from the capacitor itself quality accounts for about 15 to 45%.
Can be seen from the above data, the main failure modes of the capacitor is associated with improper selection and use.
Therefore, completes the choice and application of electrolytic capacitor, to ensure the quality of military products and reliability is of great importance.
So choose a good electrolytic capacitor factory is particularly important.
The choice of electrolytic capacitor in military electronic products, in order to guarantee the reliability of the whole system, choose the electrolytic capacitor, should follow the following principles: (
As far as possible choose listed in military electronic components list (
As far as possible choose optimization components listing products (
The quality levels of correct selection of components;
Try to choose standard and general components, careful selection of new varieties and non-standard components;
In providing components list, the meaning of the logo must be clear components, to avoid purchasing back working components do not conform to the requirements of the reliability of the whole system.
Designers in selecting capacitor, want to know about the main technical performance of the electrolytic capacitor, its capacitance and working voltage, leakage current and loss tangent value, temperature characteristic and impedance frequency characteristic, reverse voltage, the respect such as storage performance and price comparison.
The capacitor should be paid more attention to the use of material, the most commonly used material is Z5U, this kind of material stable performance, high dielectric coefficient, great capacity of capacitor, the resonance frequency can reach 1 ~ 20 MHZ;
The highest available to 50 MHz.
Another commonly used material is NPO, this kind of material has good frequency characteristic, but low dielectric constant, small capacity, generally does not use under 10 MHz.
Electrolytic capacitor aluminum electrolytic capacitor and tantalum electrolytic capacitor two kinds big.
Tantalum electrolytic capacitor, and liquid solid tantalum electrolytic capacitor tantalum capacitor.
Three types of capacitor have different characteristics, when the choice should be different.
The advantage of aluminum electrolytic capacitor is aluminium production in our country wide distribution, low prices, big, light weight, has healing properties.
The downside is dielectric loss, poor insulation performance (
Leakage current big)
Aside the, big capacity deviation with effect.
Plus is generally use aluminum as the shell of the gas seal components, so the reliability is poorer.
To adapt to the environment temperature range narrow, especially negative temperature characteristic is poor, is commonly -
Individual kind of product can reach
40 ℃, the military specifications for - CDK series
Is suitable for low requirements for environmental conditions of the general civil electronic products and the high reliability requirement is part of the military ground electronic machine.
Compared with aluminum electrolytic capacitor tantalum electrolytic capacitor, the advantage is wide temperature range, is commonly -
Tantalum oxide film of the insulation resistance is aluminium oxide film 2 times, so the small leakage current;
Within the scope of the semiconductor devices working voltage (
Refer to below 150 V)
, the same capacity of tantalum capacitor 2 times than aluminum electrolytic capacitor is small in size, and has a small loss, stable performance, long service life, high reliability advantages.
Tantalum capacitor is suitable for military electronic equipment, its disadvantage is that the price is high, limited to the cost, so few dosage.
Because the CA42 tantalum capacitor using the epoxy resin coating, thus greatly reduces the price of solid tantalum capacitors, so part of the civil machine also has the batch.
Because the CA42 epoxy resin solid tantalum capacitors are packing element, do not become a military machine, using the environment conditions in military products whole sealing solution of tantalum capacitor should be adopted.
Electrolytic capacitor dielectric loss, and wide capacity error, insulation performance is poor, is only suitable for use in a variety of 50 ~ 100 Hz electronic equipment, and the power of the power frequency filtering in the low frequency circuit by-pass, coupling capacitance, or low frequency circuit of capacitance error is not high.
Liquid tantalum capacitor leakage current is small, the working voltage of the electric capacity of unit volume and product particularly large, especially suitable for large capacity under the condition of high voltage circuits.
But, this kind of capacitor has the acid liquid, if in the event of leakage, may make the PCB wiring short circuit, which cause serious machine fault, so, the military electronic equipment is prohibited to use liquid tantalum capacitor.
However, with the development of science and technology, some units have been basically solved the sealing problem of liquid tantalum capacitor, liquid tantalum capacitor has meet military specifications requirements, its reliability level has reached a level 6.
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