The full name of SMD capacitor is: multilayer (laminated, laminated) chip ceramic capacitor, also known as SMD capacitor, chip capacitor.
The role of capacitance
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1) bypass
Bypass capacitor is an energy storage device that provides energy for local equipment. It can make the output of voltage regulator uniform and reduce the load demand.
Just like a small rechargeable battery, the bypass capacitor can charge and discharge the device. In order to minimize the impedance, the bypass capacitor should be as close as possible to the power supply pin and the ground pin of the load device.
This can well prevent the noise caused by the rise of ground potential and excessive input value. The ground potential is the voltage drop when the ground connection passes through a large current burr.
2) Decoupling
Decoupling, also called decoupling. As far as the circuit is concerned,
It can always be divided into driving source and driving load. If the load capacitance is relatively large, the driving circuit should charge and discharge the capacitance.
To complete the signal jump, the current is relatively large when the rising edge is steep.
Thus, the driving current will absorb a large supply current. Because the inductance and resistance in the circuit (especially the inductance on the chip pin will rebound), this current is actually a kind of noise compared with the normal situation, which will affect the normal work of the previous stage. This is called "coupling".
Decoupling capacitor acts as a "battery" to meet the change of driving circuit current and avoid mutual coupling interference.
It is better understood by combining bypass capacitors and decoupling capacitors. Bypass capacitor is actually decoupled, but generally refers to high-frequency bypass, which is a low-impedance leakage prevention method to improve high-frequency switching noise. The high-frequency bypass capacitance is generally small, which is generally 0. 1μF and 0.0 1μF according to the resonance frequency.
Wait; The capacity of decoupling capacitors is generally large, which may be10 μ f.
Or larger, depending on the variation of the distribution parameters and the driving current in the circuit. Bypass takes the interference in the input signal as the filtering object, and decoupling takes the interference in the output signal as the filtering object to prevent the interference signal from returning to the power supply. This should be their essential difference.
3) filtering
Theoretically (that is, assuming that the capacitance is pure capacitance), the larger the capacitance, the smaller the impedance and the higher the pass frequency. But it actually exceeds1μ f.
Capacitors are mostly electrolytic capacitors with large inductance, so the impedance will increase after high frequency. Sometimes we can see that the electrolytic capacitor of a large capacitor is connected in parallel with a small capacitor, and then the large capacitor is connected to the low frequency and the small capacitor is connected to the high frequency. The function of capacitor is to pass high resistance and low resistance and pass high frequency and low frequency. The larger the capacitance, the easier it is for low frequencies to pass. Specifically used for filtering, large capacitance (1000μF) filters out low frequency, and small capacitance (20pF) filters out high frequency. Some netizens vividly compared the filter capacitor to a "pond". Because the voltage across the capacitor does not suddenly change, it can be seen that the higher the signal frequency, the greater the attenuation. It can be said vividly that the capacitor is like a pond, and the water quantity will not change because of adding or evaporating a few drops of water. It changes the voltage into the current. The higher the frequency, the greater the peak current, thus buffering the voltage. Filtering is the process of charging and discharging.
4) Energy storage
The energy storage capacitor collects the charge through the rectifier and transmits the stored energy to the output end of the power supply through the converter lead. The rated voltage is 40 ~ 450 VDC and the capacitance is 220 ~ 150.
000μF aluminum electrolytic capacitor (such as B43504 of EPCOS Company)
Or B43505) is more commonly used. According to different power requirements, devices are sometimes connected in series, parallel or combined, and the power level exceeds 10KW.
The power supply usually uses a large slot spiral terminal capacitor.