As a passive component, the chip capacitor is often used in the power supply circuit to achieve bypass, decoupling, filtering and energy storage, etc., and the main role in the signal circuit is coupling, oscillation/synchronization and time constant. Let's add one explanation to each of these.

1. Filtering function in the power supply circuit: filtering is a very important part of the role of the chip capacitor. It's used in almost all power supply circuits. In theory (that is, if the capacitor is a pure capacitor), the larger the capacitor, the smaller the impedance, and the higher the frequency of passing. But in fact, more than 1uF capacitors are mostly electrolytic capacitors, and have a large inductance component, so the impedance will increase after high frequency. Sometimes it will be seen that there is a large capacitance electrolytic capacitor in parallel with a small capacitor, at which time the large capacitor passes the low frequency and the small capacitor passes the high frequency. The role of the capacitor is to pass high and low resistance, and pass high frequency and low frequency. The larger the capacitor, the easier the low frequency passes through, and the larger the capacitor, the easier the high frequency passes through. Specifically used in filtering, large capacitance (1000uF) filters low frequency, small capacitance (20pF) filters high frequency.

Some netizens have likened the filter capacitor to a "pond". Since the voltage at both ends of the capacitor does not change, it can be seen that the higher the signal frequency, the greater the attenuation, it can be said that the capacitor is like a pond, and the water amount will not change due to the addition or evaporation of a few drops of water. It converts changes in voltage into changes in current, and the higher the frequency, the greater the peak current, thereby buffering the voltage. Filtering is the process of charging and discharging.

2, the bypass capacitor is an energy storage device that provides energy for the local device, which can homogenize the output of the regulator and reduce the load demand. Just like a small rechargeable battery, the bypass capacitor can be charged and discharge power to the device. To minimize impedance, the bypass capacitor should be as close to the power supply pin and ground pin of the load device as possible. This can well prevent the ground potential elevation and noise caused by too large input value. Ground bounce is the voltage drop when the ground connection passes through a large current burr.

3, to lotus root, also known as the solution of lotus root. In terms of the circuit, it is always possible to distinguish between the driving source and the driven load. If the load capacitance is relatively large, the drive circuit must charge and discharge the capacitor to complete the signal jump, when the rising edge is steep, the current is relatively large, so that the drive current will absorb a large power current, due to the inductance in the circuit, the resistance (especially the inductance on the chip pin, will produce rebound), This current is actually a noise relative to the normal situation, which will affect the normal operation of the front stage. That's coupling. Decoupling capacitor is to play the role of a battery, to meet the change of the drive circuit current, to avoid mutual coupling interference. Combining bypass capacitors and de-coupling capacitors will be easier to understand. The bypass capacitor is actually de-coupled, but the bypass capacitor generally refers to the high-frequency bypass, that is, to improve the high-frequency switching noise of a low impedance leakage path. The high-frequency bypass capacitor is generally small, according to the resonance frequency is generally 0.1u, 0.01u, etc., and the decoupling capacitor is generally large, 10uF or larger, according to the distribution parameters in the circuit and the change in the drive current to determine the size. Bypass is to filter the interference in the input signal as the object, and decoupling is to filter the interference in the output signal as the object to prevent the interference signal from returning to the power supply. This should be their essential difference.

4, the energy storage capacitor collects charge through the rectifier, and transmits the stored energy to the output end of the power supply through the converter lead. Aluminum electrolytic capacitors with voltage ratings of 40 ~ 450VDC and capacitance values between 220 ~ 150000uF are more commonly used. Depending on the power requirements, the device will sometimes be in series, parallel or a combination of the form, for power levels of more than 10KW power supplies, usually use a larger volume of can-shaped spiral terminal capacitors.