The AC filter capacitor plays a very important role in the switching power supply. How to select the AC filter capacitor correctly, especially the output filter capacitor, is a problem that every engineering technician is very concerned about.

The type of capacitor should be selected according to the circuit requirements. 

For low-frequency circuits and DC circuits with low requirements, paper capacitors or low-frequency ceramic capacitors can generally be selected. In the high-frequency circuit, when the electrical performance requirements are high, mica capacitor, high-frequency ceramic capacitor or through-core ceramic capacitor can be selected. Metallised film capacitors can be used in intermediate-frequency and low-frequency circuits with high requirements. In the power filtering and decoupling circuits, aluminum electrolytic capacitors are generally used. For circuits requiring high reliability and stability, mica capacitors, tantalum electrolytic capacitors and metallized film capacitors should be selected. For high-voltage circuits, high-voltage ceramic capacitors or metallized film capacitors should be selected. For tuning circuits, variable capacitors and fine-tuning capacitors should be selected.

Reasonably determine the capacitance and allowable deviation of the capacitor. 

In low-frequency coupling and decoupling circuits, generally, the capacitance of the capacitor is not too strict, as long as a slightly larger capacitance is selected according to the calculated value. In timing circuits, oscillation circuits and tone control circuits, the capacitance of capacitors is strictly required. Therefore, the nominal value of the selected capacitance should be consistent with or close to the calculated capacitance value as far as possible, and the capacitor with high accuracy should be selected as far as possible.