1, filtering effect, in the power supply circuit, the rectifier circuit will turn the AC into a pulsating DC, and after the rectifier circuit is connected to a large-capacity electrolytic capacitor, using its charge and discharge characteristics (energy storage), so that the pulsating DC voltage after rectification becomes a relatively stable DC voltage. In practice, in order to prevent the power supply voltage of each part of the circuit from changing due to load changes, the output end of the power supply and the power input end of the load are generally connected with tens to hundreds of micromethods of electrolytic capacitors. Because the large-capacity electrolytic capacitor generally has a certain inductance, the high-frequency and pulse interference signals can not be effectively filtered out, so a capacitor with a capacity of 0.001-0.lPF is connected in parallel at both ends to filter out the high-frequency and pulse interference.

　　2, coupling: In the transmission and amplification of low-frequency signals, in order to prevent the static operating points of the front and back two stages of the circuit from influencing each other, capacitive coupling is often used. In order to prevent the loss of the low-frequency component of the signal from being too large, electrolytic capacitors with larger capacity are generally used.