Correct selection of capacitors
(1) The type of capacitor should be selected according to the circuit requirements. For low-frequency circuits and DC circuits that are not demanding, paper capacitors or low-frequency ceramic capacitors are generally available. 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. Plastic film capacitors are available for higher frequency and low frequency circuits. In the power supply filtering and decoupling circuit, an aluminum electrolytic capacitor is generally selected. For circuits requiring high reliability and high stability, mica capacitors, 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 the low-frequency coupling and decoupling circuit, the capacitance requirement of the capacitor is generally not too strict, as long as the slightly larger capacitance is selected according to the calculated value. In circuits such as timing circuits,oscillation circuits, and tone control, the capacitance requirements of capacitors are relatively strict. Therefore, the nominal value of the selected capacitance should be as close as possible to the calculated capacitance value or as close as possible. In some special circuits, the capacitance of the capacitor is often very precise. In this case, a high-precision capacitor with an allowable deviation of ±0.1% to ±0.5% should be used.
(3) The working voltage of the selected capacitor should meet the circuit requirements. Under normal circumstances, the rated voltage of the capacitor should be 1.2 to 1.3 times the actual working voltage. For circuits with high operating temperatures or poor stability. The rated voltage of the capacitor should be considered for derating, leaving a larger margin. If the operating voltage in the circuit where the capacitor is located is higher than the rated voltage of the capacitor, the capacitor is often prone to breakdown, so that the entire circuit cannot work normally. The rated voltage of the capacitor is generally referred to as the DC voltage. If it is to be used in an AC circuit, it should be selected according to the characteristics and specifications of the capacitor. If it is to be used for a pulsating circuit, it should be selected according to the sum of the AC and DC components not exceeding the rated voltage of the capacitor.
(4) Capacitors with large insulation resistance, low dielectric loss, and low leakage current are preferred.
(5) The capacitor should be selected according to the working environment of the capacitor. The performance parameters of the capacitor are closely related to the conditions of the environment in which it is used. Therefore, when choosing a capacitor, you should pay attention to:
1. Capacitors used under high temperature conditions should use capacitors with high operating temperature;
2. In the circuit working in a humid environment, a sealed capacitor with good moisture resistance should be used;
3. For capacitors used under low temperature conditions, cold-resistant capacitors should be used, which 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 types of capacitors. When choosing, the shape and pin size of the capacitor should be selected according to the actual situation.
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