1.The type of capacitor should be selected according to the circuit requirements. For low-frequency circuits and DC circuits with low requirements, paper capacitors can generally be used, and low-frequency monitoring capacitors can also be used . In high-frequency circuits, when the electrical performance requirements are high, mica capacitors, high-frequency ceramic capacitors or through-core ceramic capacitors can be used. In medium-frequency and low-frequency circuits with higher requirements, plastic film capacitors can be used. In electromagnetic filtering and decoupling circuits, aluminum electrolytic capacitors are generally used. For circuits requiring high reliability and stability, mica capacitors, paint film capacitors or tantalum electrolytic capacitors should be used. For high-voltage circuits, high-voltage ceramic capacitors or other types of high-voltage capacitors should be used. For tuned circuits, variable capacitors and trimmer capacitors should be used.
2. Reasonably determine the capacitance and allowable deviation of the capacitor. In low-frequency coupling and sacrificing circuits, the capacitance requirements of the capacitor are generally not strict, and it is enough to select a slightly larger capacitance based on the calculated value. In circuits such as timing circuits, oscillation circuits, and tone control circuits, the capacitance requirements of capacitors are relatively strict. Therefore, the nominal value of the capacitance selected should be consistent with or as close as possible to the calculated capacitance value. Capacitors with high precision should be selected as much as possible. . In some special circuits, the capacitance of the capacitor is often required to be very precise. In this case, a high-precision capacitor with an allowable deviation within the range of ±0.1% ~ ±0.5% should be selected.
3.The working voltage of the selected capacitor should meet the circuit requirements. In general, the rated voltage of the selected capacitor should be 1.2-1.3 times the actual working voltage. For circuits with high working environment temperatures or poor stability, derating the rated voltage of the capacitor should be considered to leave a larger margin.
4.If the working voltage of the circuit in which the capacitor is located is higher than the rated voltage of the capacitor, the capacitor is often prone to breakdown, making the entire circuit unable to work properly.The rated voltage of a capacitor generally refers to the DC voltage. If it is used in an AC circuit, it should be selected according to the characteristics and specifications of the capacitor; if it is used in a pulsating circuit, it should be selected based on the fact that the sum of the AC and DC components must not exceed the rated voltage of the capacitor.
5. Give priority to capacitors with large insulation resistance, small dielectric loss and small leakage current.
5.1 Capacitors should be selected according to the working environment of the capacitor. The performance parameters of capacitors are closely related to the conditions of the use environment, so when selecting capacitors you should pay attention to:
①. Capacitors used under high temperature conditions should be capacitors with high operating temperatures;
②. For circuits working in a humid environment, sealed capacitors with good moisture resistance should be used;
③. Capacitors used under low temperature conditions should choose cold-resistant capacitors. This is especially important for electrolytic capacitors, because ordinary electrolytic capacitors will cause the electrolyte to freeze and fail under low temperature conditions.
6.When selecting capacitors , the requirements of the installation site should be considered.
There are many shapes of capacitors. When selecting, the shape and pin size of the capacitor should be selected according to the actual situation. For example, as a capacitor for high-frequency bypass, it is best to use a feedthrough capacitor, which is not only easy to install but can also be used as a binding post.
7.Pay attention to the frequency response of the capacitor. Capacitors perform differently at different frequencies. When selecting a capacitor, you should fully understand the performance parameters of the capacitor at different frequencies to ensure that it can perform well in the circuit it is used in. For circuits with large frequency changes, capacitors with better frequency response can be used, such as ceramic capacitors, film capacitors, etc.
8.Consider the life and reliability of the capacitor. The longevity and reliability of capacitors are critical to their application in circuits. When selecting capacitors, capacitors with long life and high reliability should be selected based on the service life of the circuit and environmental conditions. For example, capacitors that work under harsh conditions such as high temperature and high voltage should use capacitors with longer life and higher reliability, such as tantalum electrolytic capacitors, gallium nitride capacitors, etc.
9.Pay attention to the stability of the capacitor. The stability of a capacitor has an important impact on its performance in a circuit. When selecting a capacitor, you should fully understand the stability of the capacitor during long-term use to ensure that it can maintain stable performance in the circuit. For circuits with higher stability requirements, capacitors with better stability can be used, such as mica capacitors, paint film capacitors, etc.
10.Reasonably select the size and weight of the capacitor. The size and weight of a capacitor have a certain impact on its application in a circuit. When selecting capacitors, capacitors of appropriate size and weight should be selected based on the space constraints and installation requirements of the circuit. For example, in circuits with limited space, miniaturized and lightweight capacitors can be used, such as film capacitors, ceramic capacitors, etc.
To sum up, the selection and application of capacitors should fully consider the circuit requirements, capacitor type, capacitance and allowable deviation, operating voltage, insulation resistance, dielectric loss, leakage current, working environment, installation site and other factors. Only by comprehensively considering these factors can we ensure that the capacitor performs well in the circuit and ensures the normal operation of the circuit. At the same time, when selecting capacitors, you should also pay attention to the frequency response, life, reliability, stability, size and weight requirements of the capacitor to meet the specific application needs of different circuits. By rationally selecting capacitors, we can give full play to the advantages of capacitors in the circuit and improve the performance and reliability of the circuit.