What are the applications of SMD capacitors in the electrical field?

Chip capacitors, as passive components, are commonly used in power circuits for functions such as bypass, decoupling, filtering, and energy storage. In signal circuits, their main functions include coupling, oscillation/synchronization, and time constant. Let's explain each of these separately

  1. Filtering function in power supply circuit: Filtering is a very important part of the function of chip capacitors. It is used in almost all power circuits. In theory (assuming that the capacitance is pure), the larger the capacitance, the smaller the impedance, and the higher the frequency of passage. However, in fact, most capacitors above 1uF are electrolytic capacitor, which have a large inductance component, so the impedance will increase when the frequency is high. Sometimes it can be seen that a electrolytic capacitor with a large capacitance is connected in parallel with a small one. At this time, the large capacitance is connected with low frequency and the small capacitance is connected with high frequency. The function of a capacitor is to pass through high resistance and low resistance, while passing through high frequency and low frequency resistance. The larger the capacitance, the easier it is to pass through low frequencies, and the larger the capacitance, the easier it is to pass through high frequencies. Specifically used in filtering, large capacitors (1000uF) filter low frequencies and small capacitors (20pF) filter high frequencies Some netizens once compared the filtering capacitor to a "pond". Due to the fact that the voltage at both ends of the capacitor does not suddenly change, it can be seen that the higher the signal frequency, the greater the attenuation. It can be vividly said that the capacitor is like a pond, without any changes in water volume caused by 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. Bypass capacitors are energy storage devices that provide energy for local devices, which can homogenize the output of the voltage regulator and reduce load demand. Just like a small rechargeable battery, the bypass capacitor can be charged and discharged into the device. To minimize impedance, the bypass capacitor should be as close as possible to the power supply pin and ground pin of the load device. This can effectively prevent ground potential rise and noise caused by excessive input values. A ground bomb is the voltage drop when the ground connection passes through a large current burr 3. Removing lotus roots, also known as uncoupling lotus roots. From a circuit perspective, it is always possible to distinguish between the source of the drive and the load being driven. If the load capacitance is relatively large, the driving circuit needs to charge and discharge the capacitance in order to complete the signal jump. When the rising edge is steep, the current is relatively high, so the driving current will absorb a large amount of power current. Due to the inductance and resistance in the circuit (especially the inductance on the chip pins, it will rebound), this current is actually a type of noise compared to normal conditions, It will affect the normal operation of the previous level. This is coupling. The decoupling capacitor serves as a battery to meet the changes in driving circuit current and avoid mutual coupling interference. Combining bypass capacitors with decoupling capacitors will be easier to understand. The bypass capacitor is actually decoupled, but it generally refers to high-frequency bypass, which means adding a low impedance leakage path to high-frequency switching noise. The high-frequency bypass capacitor is generally relatively small, based on the resonance frequency of 0.1u, 0.01u, etc., while the decoupling capacitor is generally larger, which is 10uF or greater, determined by the distributed parameters in the circuit and the variation of the driving current. Bypass is to filter out the interference in the input signal, while decoupling is to filter out the interference in the output signal, preventing the interference signal from returning to the power source. This should be their fundamental difference 4. Energy storage capacitors collect charges through rectifiers and transmit the stored energy to the output terminal of the power supply through converter leads. The Aluminium electrolytic capacitor with voltage rating of 40~450VDC and capacitance value of 220~150000uF is commonly used. According to different power supply requirements, devices may sometimes be in series, parallel, or their combination. For power supplies with power levels exceeding 10KW, larger can shaped spiral terminal capacitors are usually used