The function of bypass capacitor is to homogenize the input voltage and reduce the influence of noise on the later stage. Store energy, and compensate the voltage in time when the external signal changes too fast. In the printed circuit board (PCB), the bypass capacitor of the power supply should be designed according to the layout that the power supply first passes through a large capacitor and then passes through a small capacitor. Only in this way can the bypass capacitor be effectively displayed.
Decoupling capacitor and bypass capacitor have similar functions, both of which have the function of filtering out interference signals, except that the bypass capacitor is aimed at the input signal, while the decoupling capacitor is aimed at the output signal. In short, it is called bypass varactor at the signal input end and decoupling capacitor at the signal output end. The basic characteristic of the capacitor is to isolate DC from AC. When an AC signal with DC bias passes through the coupling capacitor, the DC bias will become zero because it cannot pass through the capacitor, as shown in the following figure.
Capacitors are often used in audio circuits for coupling. As shown in the figure below.
The normal operation of MIC requires DC voltage, and the resistor 15K is used to provide current to ensure the normal operation of MIC. The coupling capacitor 22uF is added to MIC to eliminate the DC signal in the AC signal output by MIC, so that the AC signal can enter the amplifier and make full use of the characteristics of positive and negative power supplies. If the signal has a DC bias, then the signal has only half the dynamic performance.
The function of filtering is to filter out impurities, low frequency with large capacitance and high frequency with small capacitance. Capacitor is used for filtering because the voltage of the capacitor can't change suddenly. Moreover, for high-frequency signals, the impedance of the capacitor is low, and the noise signal on the signal line can be bypassed, so as to achieve the function of filtering. The principle is shown in the following figure.
Of course, when filtering, capacitors are usually used with resistors or inductors to form RC or LC filtering circuits, which will have a better effect.
Capacitors are very common for storing energy, and are generally used in power supply, as shown in the following figure.
If a large capacitor is not added to the output power of the power IC, when the IC needs to consume current, the power chip and IC in the previous stage usually do not respond quickly because of the long distance, so the voltage of the IC will drop and it will not work normally. Therefore, capacitor energy storage is added at the pin of the chip to provide energy for IC quickly, which can prevent voltage drop.
In practical application, the output power of the power IC is 5V1A, and the power of the load is 5V0.5A when it is working normally. However, the instantaneous power of the load is at the maximum of 5V2A, and the duration is ms level. If the power IC is used alone to provide energy for the load, it is obvious that the power of the previous stage cannot be provided when the auxiliary instantaneous current needs 2A. At this time, we will connect a plurality of large capacitors in parallel at the front stage of the load to provide the load current at the back stage at high power.
