Chip capacitor
1. Bypass
Bypass capacitor is an energy storage device that provides energy for local equipment. It can even out the output of the voltage regulator and reduce load requirements. Like a small rechargeable battery, the bypass capacitor can be charged and discharged into the device. In order to minimize the impedance, the bypass capacitor should be as close as possible to the power supply pin and ground pin of the load device. This can well avoid raising the ground potential and noise caused by too large input values. Ground potential is the voltage drop across the ground connection when a large current spike passes through it.
2. Decoupling
, also known as decoupling. From a circuit perspective, it can always be distinguished into a driven source and a driven load. If the load capacitance is relatively large, the driving circuit must charge and discharge the capacitor to complete the signal transition. When the rising edge is relatively steep, the current is relatively large, so the driving current will absorb a large power supply current, because the circuit The inductance and resistance (especially the inductance on the chip pins will cause rebound), this current is actually a kind of noise compared to normal conditions, which will affect the normal operation of the front stage. This is the so-called " coupling".
The decoupling capacitor functions as a "battery" to meet the changes in the drive circuit current and avoid mutual coupling interference.
Combining bypass capacitors and decoupling capacitors will make it easier to understand. The bypass capacitor is actually decoupled, but the bypass capacitor generally refers to a high-frequency bypass, which means to provide a low-impedance leakage path for high-frequency switching noise. High-frequency bypass capacitors are generally relatively small, usually 0.1μF, 0.01μF, etc. depending on the resonant frequency; while the capacity of the decoupling capacitor is generally larger, maybe 10μF or larger, depending on the distribution parameters in the circuit and the changes in the drive current. to be sure. Bypass uses the interference in the input signal as a filtering object, while decoupling uses the interference in the output signal as a 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 capacitor is a pure capacitor), the larger the capacitor, the smaller the impedance, and the higher the passing frequency. But in fact, most capacitors exceeding 1μF are electrolytic capacitors., has a large inductance component, so the impedance will increase when the frequency is high. Sometimes you will see an electrolytic capacitor with a large capacitance connected in parallel with a small capacitor. At this time, the large capacitor passes low frequency and the small capacitor passes high frequency. The function of the capacitor is to pass high frequencies and resist low frequencies, and to pass high frequencies and resist low frequencies. The larger the capacitor, the easier it is for low frequencies to pass through. Specifically used in filtering, large capacitors (1000μF) filter low frequencies, and small capacitors (20pF) filter high frequencies. Some netizens once compared filter capacitors to "ponds". Since the voltage at both ends of the capacitor will not change suddenly, 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, and the water volume will not change due to the addition of a few drops of water or transpiration. It converts changes in voltage into changes in 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 charges through the rectifier and transmits the stored energy to the output end of the power supply through the converter leads. Aluminum electrolytic capacitors (such as EPCOS's B43504 or B43505) with a voltage rating of 40 to 450 VDC and a capacitance value of 220 to 150 000 μF are more commonly used. According to different power requirements, equipment sometimes uses series connection, parallel connection or a combination thereof. For power supplies with power levels exceeding 10KW, larger can-shaped screw terminal capacitors are generally used.