Role: Power input/output filter capacitors, mainly used to stabilise the output, good for voltage regulation.
What are the main functions of capacitors?
1. Voltage regulation
Power supply and ground between the capacitance of the reason there are two roles, energy storage and bypass energy storage: circuit power consumption is sometimes large, sometimes small, when the power consumption suddenly increased when there is no capacitance, the power supply voltage will be pulled down, generating noise, ringing, serious will lead to CPU reboot, this time large-capacity capacitors can be temporarily to the release of the stored electrical energy to stabilise the power supply voltage, like the relationship between the river and the reservoir of the bypass: Circuit current many times there are pulsations, such as the synchronous frequency of digital circuits, will cause the power supply voltage pulsations, this is a kind of AC noise, small-capacity electrodeless capacitors can be bypassed to the ground of this kind of noise (capacitors can be through the AC, blocking the DC, small-capacity capacitors through the frequency band is much higher than the capacitance of a large capacitor), but also to improve stability!
2. Power supply filtering
Capacitor capacity = dielectric constant area / distance = εS / d, usually ε, d is not easy to change, can only change S to change the capacity. When the capacitance is very large, S must be large, in order to reduce the volume, have to use the way of stacking, but the stacking will inevitably increase the inductance (despite the symmetrical double-wound).As you know the capacitance is actually a combination of R, L, C, so that the large capacitance of the relative inductance L is also large. For example: with 2200uF capacitor wave, for low frequency 50Hz is very good, but for high frequency (K, MHz), not useful at all, because L is too large. So the master is very concerned about the power supply filtering, will use large, medium and small three capacitors, respectively, for low, medium and high frequency to filter.
Practical application
In the DC power supply (Vcc) and ground and connect the capacitor between the capacitor can be called filter capacitor. Filter capacitor filtering power supply noise and AC components, pressure smoothing pulsating DC, storage of electrical energy, take the value of the general 100-4700uF, take the value of the load current and the purity of the power supply is related to the larger the better capacity. Sometimes in the big capacitor next to a smaller capacity capacitor, called high-frequency decoupling capacitor, is also a type of filtering used to filter out high-frequency noise in the power supply to avoid the circuit state to produce self-excitation, stabilise the circuit work. Take the value of the general 0.1-10uF, take the value and filter the frequency of the clutter.
The role of such a connection is generally called "decoupling", also known as "decoupling", "bypass" capacitance, often arranged in the power supply, IC and functional module circuits nearby. To non-inductive porcelain, monolithic capacitors are preferred.
Role is to provide a path for high-frequency signals, reduce the internal resistance of the power supply, remove the power supply and ground in the copper-laying board "go long line" of the impact of the public power supply to prevent the various parts of the circuit between the "harmful cross-linking" and so on. 10nF is commonly used.
On development boards, there are usually many 0.1uF non-electrolytic capacitors and 10uF electrolytic capacitors between the DC power supply and ground.
The purpose of these capacitors is to make the power and ground lines low impedance and the power supply close to an ideal voltage source. It's fine if you want to say it's filtering, but you need to figure out what kind of wave is being filtered. It is not the ripple of the power supply, but the ripple caused by a change in the current of a chip on the power line, so that it does not affect other chips.
Use 0.1uF non-polar capacitor and 10uF electrolytic capacitor in parallel, because the parasitic inductance of the electrolytic capacitor is relatively large, eliminating high-frequency ripple ability is poor. And non-polar capacitor parasitic inductance is small, the ability to filter out high-frequency ripple is better. But if the low-frequency requirements based on the choice of capacity, the volume of non-polar capacitors is too large, the cost is also high, electrolytic capacitors are small, the same capacity price is cheaper. Therefore, the use of two capacitors in parallel.
When you design your own circuit, should also be used in this way, and the capacitor position and alignment is very delicate.
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