The filtering function of capacitors

Capacitors have the function of storing electrical energy, which is no different from batteries, but the only difference is that capacitors do not continuously convert chemical energy into electrical energy. Therefore, their storage capacity is very limited and can only last for a short period of time. Yesterday, we also mentioned the energy calculation of capacitors: E=C（U^2）/2=QU/2=（Q^2）/2C， Directly proportional to the square of the stored charge and inversely proportional to the capacitance, it can be seen that being able to store electrical energy is one of the basic functions of a capacitor. This function is applied in many situations, such as in the "anti shaking" technology, where energy storage capacitors are used to avoid momentary voltage drops.

For ease of understanding, the above picture shows a super energy storage capacitor!

Today we will introduce another common function of capacitors, which is filtering. In single-phase rectification or three-phase rectification circuits, one or more capacitors are always connected in parallel, and this capacitor is the filtering capacitor, and this circuit is the filtering circuit. The so-called filtering circuit is to filter out the ripple in the rectified output voltage, and series capacitors are the most commonly used method. The function of the filtering circuit is to minimize the AC component in the pulsating DC voltage, retain its DC component, reduce the ripple coefficient of the output voltage, and make the waveform smoother. As shown in the picture:

This image vividly describes the function of capacitor filtering and the changes in output waveform. So, how does capacitor achieve filtering? In fact, it utilizes the charging and discharging principle of capacitors, as shown in the figure above: the input AC passes through a full wave rectification circuit and outputs a pulsating waveform voltage, which acts on the load resistance and charges the capacitor. When the rectifier diode is turned off, the capacitor discharges the load, maintaining the load voltage in a relatively stable state. This forms a filtering waveform before voltage stabilization, which is a relatively stable DC waveform. This is most widely used in the rectification circuit of frequency converters, but frequency converters often use three-phase full wave rectification circuits, and filtering capacitors are absolutely indispensable.