The difference between a variety of ceramic capacitors

Speaking of capacitors, all kinds of names can make people dizzy, film capacitors, ceramic capacitors, safety Y capacitors, high-voltage capacitors, etc. In fact, high-voltage ceramic capacitors are also called, such as bypass capacitors, decoupling Capacitors, filter capacitors, storage capacitors, etc., in fact, the principle is the same, that is, the use of low-impedance characteristics of the AC signal, which can be seen by the equivalent impedance formula of the capacitor: Xcap= 1/2лfC, the higher the operating frequency, the larger the capacitance value, the smaller the impedance of the capacitor.

In the circuit, if the main function of the safety capacitor is to provide a low-impedance path to the AC signal, it is called a bypass ceramic capacitor; if it is mainly to increase the AC coupling between the power supply and the ground, reduce the influence of the AC signal on the power supply, It can be called decoupling ceramic capacitor; if it is used in the filter circuit, it can also be called filter ceramic capacitor; in addition, for DC voltage, ceramic capacitor can also be used as circuit energy storage, using the discharge to function as a battery. . In reality, the role of capacitors is often multifaceted. We don't have to think too much about how to define them.

Decoupling ceramic capacitors act as a battery to meet the changes in the drive circuit current and avoid mutual coupling interference. Both decoupling and bypassing can be seen as filtering. Decoupling ceramic capacitors are equivalent to batteries, avoiding voltage drops due to sudden changes in current, equivalent to filter ripple. The specific capacitance value can be calculated according to the magnitude of the current, the desired ripple size, and the magnitude of the action time. Decoupling ceramic capacitors are generally large and are essentially ineffective for higher frequency noise.

The bypass ceramic capacitor is for high frequency, that is, the frequency impedance characteristic of the capacitor is utilized. Capacitors can generally be viewed as an RLC series model. At a certain frequency, resonance occurs, and the impedance of the capacitor is equal to its ESR. If you look at the frequency impedance plot of the capacitor, you will find that it is generally a V-shaped curve. The specific curve is related to the medium of the capacitor, so the choice of bypass ceramic capacitor also considers the medium of the capacitor. A safer method is more than a few capacitors.

In the electronic circuit, the decoupling capacitor and the bypass capacitor both play an anti-interference function. The position of the capacitor is different, and the calling is different. For the same circuit, the bypass capacitor uses the high-frequency noise in the input signal as the filtering object to filter the high-frequency noise carried by the pre-stage, and the decoupling capacitor is also called decoupling. Capacitance is to filter the interference of the output signal. A capacitor that bypasses the high-frequency component of an AC signal mixed with a high-frequency current and a low-frequency current is referred to as a "bypass capacitor."