Murata chip capacitor
The chip capacitor is used as a passive component. The functions frequently used in the power supply circuit are: the functions of bypass, decoupling, filtering and energy storage. The main functions of the signal circuit are coupling, oscillation/synchronization and time constant. The role. Below we will add an explanation to each of these.
1, the filter function in the power circuit: filtering is a very important part of the role of chip capacitors. It is used in almost all power circuits. Theoretically (that is, assuming the capacitor is a pure capacitor), the larger the capacitance, the smaller the impedance and the higher the frequency of passing. However, in fact, most of the capacitors exceeding 1 uF are electrolytic capacitors, which have a large inductance component, so the impedance will increase after the frequency is high. Sometimes you will see a small capacitor with a larger capacitance and a small capacitor. At this time, the large capacitor passes through the low frequency and the small capacitor passes through the high frequency. The function of the capacitor is to pass the high impedance and low frequency. The larger the capacitance, the easier the low frequency passes, and the higher the capacitance, the easier it is to pass. Specifically used in filtering, large capacitor (1000uF) filter low frequency, small capacitor (20pF) filter high frequency.
Some netizens have compared filter capacitors to "water ponds." Since the voltage across the capacitor does not change, it can be seen that the higher the signal frequency, the greater the attenuation. It can be said that the capacitor is like a pond, and the water quantity will not be changed due to the addition or evaporation of a few drops of water. It converts the change in voltage into a change in current. The higher the frequency, the larger the peak current, which buffers the voltage. Filtering is the process of charging and discharging.
2. The bypass capacitor is an energy storage device that supplies energy to the local device. It can equalize the output of the regulator and reduce the load demand. Like a small rechargeable battery, the bypass capacitor can be charged and discharged to the device. To minimize impedance, the bypass capacitor should be as close as possible to the power supply and ground pins of the load device. This can well prevent ground potential elevation and noise caused by excessive input values. The ground bounce is the voltage drop when the ground connection is passed through a large current glitch.
3, From the circuit, it can always be distinguished as the source of the drive and the load being driven. If the load capacitance is relatively large, the drive circuit must charge and discharge the capacitor to complete the signal transition. When the rising edge is steep, the current is relatively large, so that the driven current will absorb a large supply current, due to the circuit. The inductance, the resistance (especially the inductance on the chip pin, will produce a rebound), this current is actually a kind of noise compared to the normal situation, which will affect the normal operation of the previous stage. This is the coupling. The decoupling capacitor acts as a battery to meet the changes in the drive circuit current and avoid mutual coupling interference. Combining the bypass capacitor with the decoupling capacitor will be easier to understand. The bypass capacitor is actually decoupled, except that the bypass capacitor generally refers to the high-frequency bypass, which is to increase the low-frequency leakage prevention path for the high-frequency switching noise. The high-frequency bypass capacitor is generally small. According to the resonant frequency, it is generally 0.1u, 0.01u, etc., and the decoupling capacitor is generally large, 10uF or larger, which is determined according to the distributed parameters in the circuit and the variation of the driving current. Bypass is to filter the interference in the input signal, and decoupling is to filter the interference of the output signal to prevent the interference signal from returning to the power supply. This should be their essential difference.
4. The energy storage capacitor collects charge through the rectifier and transfers the stored energy to the output of the power supply through the converter lead. Aluminum electrolytic capacitors with a voltage rating of 40 to 450 VDC and a capacitance value between 220 and 150 000 uF are more commonly used. Depending on the power requirements, the devices are sometimes connected in series, in parallel, or a combination thereof. For power supplies with power levels above 10 kW, bulky screw-type terminal capacitors are typically used.
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