The so-called capacitive, hold and release the electric charge of electronic components.
The basic working principle of the capacitor is charging the discharge and, of course, rectifying, oscillating, as well as other functions.
In addition the capacitance of the structure is very simple, positive and negative electrode consists of two pieces and trapped in the middle of the insulation.
As one of the capacitance of passive components, which are the following: 1, applied to the power circuit, bypass, decoupled, filtering and storage role
1) bypass
Bypass capacitor for the local device provides energy for energy storage devices, it can make the regulator output homogenization, reduce your workload requirements. Just like small rechargeable battery, the bypass capacitor can be charged and discharged to the device. To minimize the impedance, bypass capacitor to be as close as possible to load device power supply pins and pins. This can be a good protection against input value too large to cause the ground potential elevation and noise. Ground bounce is connected at a time through high current Burr's voltage drop.
2) go to Lotus
Go to Lotus, also known as decoupling. From the circuit, it can always be divided-driven source and is driven by the load. If the load capacitor is relatively large, driving circuit to capacitance charging, discharging, to complete the signal the hopping, the steep rise in comparison, the current is relatively large, so driven currents will absorb a large supply current, circuit inductance, resistance (especially the chip on the inductance, will have a rebound), the current relative to the normal case is really a noise, affect the normal work of the former level. This is coupled. Decoupled capacitance is played the role of a battery, meet the driver circuit current changes, avoid mutual coupling interference. Will bypass capacitors and to integrate Lotus capacitor will be easier to understand. Bypass capacitor real isalso coupled to, just bypass capacitor generally refers to high-frequency bypass, to high-frequency switching noise increase a low impedance leakage prevention approaches. High-frequency bypass capacitor is generally smaller and are usually based on the resonant frequency, 0.01u, 0.1u away coupling capacitor is generally relatively large, 10uF or greater, depending on the circuit of distribution parameters, as well as driving current changes size to determine.
Overall bypass is to input signal interference as a filter object, and the decoupling is to output signal interference as filtering objects, preventing interference signals return to power. This should be the essential difference between them.
3) filtering
In theory (that is, assuming that the capacitor capacitance for pure) said that the larger the capacitance, the lower the impedance, the higher the frequency also adopted. But in fact exceed 1uF Capacitor consists mostly of electrolytic capacitors, there are a lot of inductance ingredients, so the frequency of high impedance increases after it. Sometimes you will see there is an electrical capacity larger Electrolytic Capacitor parallel a small capacitor, large capacitance-LF, small high-frequency capacitance-pass. The role of capacitance is through high-frequency low-pass, low-resistance. Low-frequency capacitance greater, more easily through the smaller high-frequency capacitors easier to pass. Specific use in filtering, large capacitance (1000uF) filter LF, small capacitor (20pF) filter high frequency. Because of the capacitor voltage not mutations, so the higher the frequency, signal attenuation, the larger the image can be said that this capacitance, as a result few drops of acceding to or caused by the evaporation of water. It changes the voltage into current changes, the higher the frequency, the greater the peak current, thereby cushioning the voltage. Filtering is the process of charging and discharging.
In the power circuit, circuit AC into DC and the pulsing in rectifier circuit after access a larger capacity electrolytic capacitors, use its charge and discharge characteristics, so that the rectification of pulsating DC voltage into a relatively stable DC voltage. In practice, in order to prevent circuit parts supply voltage changes due to load, so the resulting change in power output and load of the power input General received dozens to hundreds of micro-method of electrolytic capacitors, due to the large volume of electrolytic capacitor is generally has a high-frequency inductive, and pulse interference signal cannot be effective in filtering out, at the ends of the parallel of a capacity of 0.001--0.lpF Capacitance to filter out high frequency and pulse interference.
4) energy storage
Energy storage-capacitors charge through rectifier collection and storage of energy through the converter inlet to the power output. Voltage rating of 40 ~ 450VDC, capacitance in 220 ~ 150 000uF between aluminum electrolytic capacitors (e.g. EPCOS company B43504 or B43505) is more commonly used. According to the different power requirements, the devices are sometimes used in series, parallel, or their combination of form, the power level exceeds 10KW of power, usually large jar-shaped screw terminal capacitor. 2, applied to the signal circuit, the main complete coupling, oscillation/sync and time constants:
1) decoupling
For example, the transistor amplifier emitter has a self-sufficient bias resistance, while making the signal generation voltage drop feedback to input form input and output signal coupling, the resistance is produced by coupling components, if the resistance ends a capacitor in parallel, since appropriate capacity capacitor on the AC signal lower impedance, which reduces the resistance of coupling effects, therefore calls this a decoupling capacitor capacitance.
2) oscillation/synchronization
Including RC, LC oscillator and Crystal load capacitance fall into this category.
3) time constant
This is the common R, C-line, consisting of the integral circuits. When the input signal voltage at the input side, the capacitor (C) the voltage to rise gradually. The charging current is rising as the voltage decreases. Electric current through a resistance (R), and capacitance (C) of the property by the following equation: I = (V/R) e-(t/CR) concluded by Electrolytic Capacitor
- the use matters needing attention: electrolytic capacitors with positive and negative polarity, therefore when used in the circuits cannot reverse the join. In the power circuit, output is voltage cathode electrolytic capacitors for power output-side, theperformance of the grounding, the output is negative when the negative voltage output, then the positive grounding. when the power circuit of filter capacitor polarity reversed
On the filter capacitors, decoupling capacitor, bypass capacitance effects
Filter capacitors in power rectifier circuit, used to filter out the communication components. The output of the DC smoother.
Decoupling capacitor available in the amplifier circuit is not needed to talk, to eliminate the self-excited, make amplification and stable work.
Bypass capacitors used in connection with resistance, resistance to both ends by AC signal.
1. on the decoupling capacitor energy storage
- understanding of decoupling capacitor is removing high frequency interference such as RF signal, interference into by electromagnetic radiation. In fact, the chip is also nearby capacitor energy storage function, the second digit. You can put the total power as the Miyun reservoir, our building families need water, this time, the water is not direct from the reservoir so that the distance is too far away, such as water, we have the thirsty. Actual water from the top of the Tower of the building, the water tower is actually a buffer. If the micro-level, high-frequency devices at work, its current is not contiguous, and frequency is very high, and the devices VCC to total power for some distance, even if the distances are long, the frequency is high, the impedance Z = I * wL + R, line effects of inductance can be very large, can cause device in need current, can not be timely supply. While decoupling capacitor can compensate for this deficiency. This is why many circuit board in the high-frequency devices VCC pins by placing one of the reasons why small capacitor (usually in the VCC pin a decoupled capacitor in parallel so that Exchange components from the capacitor to ground. ) Active devices in the switch from high-frequency switching noi
Decoupling: removal of the device when you switch from high-frequency devices into the distribution network of RF energy. Decoupling capacitor can also provide for devices localization of DC voltage source, it reduces cross-plate surge current particularly useful.
Bypass: from the component or cable transfer out of common RF energy. This primarily by producing AC bypass eliminate unintended energy into the sensitive part, moreover can also provide baseband filtering function (bandwidth restricted).
We often see that the power supply and ground connection between a decoupling capacitor, it has three aspects: first, as the capacitor energy storage integrated circuits; the second is to filter out the high frequency noise generated by the device, cutting off its spread through power supply circuits; third, to prevent power portable noise interference on the circuit.
In electronic circuits, and decoupling capacitor and bypass capacitors are played the role of anti-interference, capacitance where it is placed, salutation won't be the same. For the same circuit, bypass (bypass) capacitor is the input signals in high frequency noise as a filter object, the former grade portable high-frequency noise filtering, and decoupling capacitors (decoupling), also known as decoupling capacitor to the output signal interference as filtering objects. +++++++++++++++++++++++++++++++++++++++++++++
Large capacitance capacitors in parallel small effect and application of principles
Large capacitance as large capacity, volume generally relatively large, and often use multi-layer winding way, which leads to a large capacitor inductance is relatively large (also called equivalent series inductance, ESL English abbreviation).
Inductor in high frequency signal impedance is very large, so large capacitance of high frequency performance is not good. While some small-capacity capacitor is just the opposite, since the capacity is small, so the volume can be very small (shortens lead, reduces ESL, because a segment of wire can also be viewed as a reactor), and often use the plate capacitor structure, so that small-capacity capacitor has a very small ESL so that it has the very good RF performance, but because of the capacity of small, low frequency signal impedance.
So, if we are to allow low-frequency, high-frequency signals can be very good, it takes a large re-capacitance and capacitance of the previous å.
Frequently used small capacitor capacitance for 0.1uF of porcelain, when more frequently, but also smaller capacitor in parallel, for example, several hundreds of pF pF. In digital circuits, typically give each chip power PIN on a capacitor in parallel to the ground 0.1uF (this decoupling capacitor capacitance is called, of course, can also be understood as a power filter capacitors, the closer the chip, the better) because in these parts of the signal is high frequency signal, using a small capacitor filter.
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