Capacitance is the most common and commonly used parts of an apparatus in circuit design, it is one of passive component, active parts of an apparatus says simply even if need can (report) the parts of an apparatus of the source calls active parts of an apparatus, need not can (report) the parts of an apparatus of the source is passive parts of an apparatus. Capacitance often also acts important role in high speed circuit.

 

The action of capacitance and utility, have a lot of kinds commonly. Be like: In bypass, go wave of lotus root, filter, store can the action of the respect; Finishing the action …… of oscillation, synchronism and time constant

 

Labor comes below:

 

1, lie between dc: Action is to prevent dc to let communication through pass.

 

 

2, bypass (go Ou) : The component of certain paralell connection in be alternating current road provides low impedance access.

 

 

 

Bypass capacitance: Bypass capacitance, call the capacitance that retreat Ou again, it is to be what a certain parts of an apparatus provides energy store can parts of an apparatus, the frequency impedance that it used electric capacity is characteristic (what the frequency character of ideal capacitance follows frequency is elevatory, impedance is reduced) , resemble a pond, it can make output voltage output even, reduce laden voltage wave motion. Bypass capacitance should stand by the pin of power supply source of laden parts of an apparatus and ground pin as far as possible, this is impedance requirement, in the picture PCB moment should notice particularly, approach time of a certain yuan of parts of an apparatus only ability restrains voltage or other because pass,be defeated by signal big and the ground potential that bring about drive up and noise, spoken parts in an opera is the communication heft with a medium direct current source, arrive through capacitance coupling in power source ground, the action that purifies direct current source reached since. If graph C1 is bypass capacitance, picture moment should stand by IC1 as far as possible

 

 

Graph C1

 

Go lotus root capacitance: Go Ou capacitance, the interference that is an output signal divides a target as filter, go Ou capacitance is equivalent to batteries, use its to charge discharge, make the signal after enlarge won’t suffer interference because of voltaic mutation. Its capacity basis the frequency of signal, control moire rate and decide, go the effect that lotus root capacitance has ” of batteries of a “ namely, satisfy the change of drive circuit electric current, avoid mutual the coupling interference between.

 

Bypass electric capacity is practical also be to go to what lotus root closes, just bypass capacitance is bypass of finger height frequency commonly, raise discharge of a low impedance to defend an approach to high frequency switch noise namely. Capacitance of high frequency bypass is compared commonly small, take 0.1F, 0.01F to wait commonly according to syntonic frequency; And go the size of coupling capacitance is average bigger, the likelihood is 10F bigger perhaps, parameter distributings in basis circuit, and the metabolic bulk of drive electric current will decide. If graph C3 is,go Ou capacitance

 

 

Graph C3

 

Their distinction: Bypass is an interference in inputting signal divide a target as filter, and go the interference that Ou is an output signal divides a target as filter, prevent to disturb signal to return power source.

 

3, coupling: Regard two circuit as the join between, allow to communicate signal to pass and transmit circuit of below one class.

 

 

 

Make the component of coupling with capacitance, it is for will before the one class after class signal is delivered, and cut off the influence of the one class after the dc of before one class is right, make circuit is debugged simple, performance is steady.

 

If do not add enlarge of capacitance communication signal to won’t be changed, it is various work place needs to redesign only, because around class is affected, debug the job to nod special difficulty, cannot come true almost when multistage.

 

4, filter wave: This to circuit character is very main, the electric capacity of CPU backside is primary it is this action.

 

 

Namely frequency F is bigger, the impedance Z of capacitance is smaller. When low frequency, capacitance C because impedance Z is bigger, useful signal can be passed smoothly; When high frequency when, capacitance C because impedance Z already very small, was equivalent to going up short circuit of high frequency noise to GND.

 

 

Filter wave action: Ideal capacitance, electric capacity is larger, impedance is smaller, the frequency that pass is taller also. Electroanalysis capacitance is to exceed 1F commonly, among them inductance component is very big, after frequency is accordingly tall instead impedance will be big. We often see can see sometimes have a capacitance bigger electroanalysis capacitance is shunt-wound a small electric capacity, actually large electric capacity connects low frequency, small electric capacity is connected high frequency, sufficient filter eliminates such ability frequency of on any account. Higher time jumps over capacitance frequency damply big, capacitance resembles a pond, a few water can’t cause its very big change, that is to say voltage wave motion is not you voltage of very great time is OK amortize, be like graph C2

 

 

Graph C2

 

5, temperature compensation: Affect to what the adaptability of temperature brings not quite in the light of other component, and undertake compensating, improve the stability of circuit.

 

 

Analysis: Because time the capacity of capacitance decided the oscillation frequency of travel oscillator, ask the capacity of time capacitance is very stable so, do not change along with environmental humidity and change, such ability make the oscillation frequency of an oscillator stable. Because this is used, the capacitance of negative temperature coefficient commentate couplet, have temperature complementary.

 

When working temperature is elevatory, the capacity of Cl is in increase, and the capacity of C2 is in reduce, the total capacity after two capacitance are shunt-wound is the sum of two capacitance capacity, because a capacity is in,increase and another is in reduce, total capacity is basic and so changeless.

 

Manage together, when thermal drop is small, the capacity of a capacitance is in reduce and another is in increase, total capacity is basic and changeless, stabilized oscillation frequency, implementation temperature compensates a purpose.

 

6, time: Capacitor and resistor cooperate to use, the time of certain circuitry is invariable.

 

 

Input signal by low to jump high when changing, through amortize 1 hind input RC circuit. The signal that the character that capacitance charges makes B is nodded can not follow input signal jumps instantly change, have a process that greatens gradually however. Should greaten when certain level, amortize 2 retroflexion, obtained a delay in output end by low to jump high change.

 

Time constant: With common RC series connection forms integral circuit to be exemple, when the input signal voltage is added when the input is carried, the voltage on capacitance rises gradually. And its charging current is reduced as the rise of voltage, resistor R and capacitance C series connection receive input signal VI, output signal V0 by capacitance C, should satisfy between RC (τ) numerical value and TW of width of input square wave: τ " " TW, this kind of circuit calls integral circuitry

 

7, harmonious: Undertake systematic tuning to the circuit related to frequency, for instance mobile phone, radio, television.

 

 

The harmonious circuit of transfiguration diode

 

Because the syntonic frequency of the oscillating circuit of Lc tuning is the function of Lc, what we discover oscillating circuit is the biggest with the smallest syntonic frequency change than the square root that compares as capacitance. Here capacitance is compared is to point to slant instead voltage most the capacitance of the hour and slant instead of the capacitance when voltage is the biggest than. Consequently, the harmonious feature curve of circuit (bias voltage one syntonic frequency) basically be a parabola.

 

8, rectification: Leave in booked time or close to shut conductor switch cell partly.

 

 

 

9, store can: Store electric energy, when be being used at must wanting, release.

 

For example camera flashlight, heating installation is waited a moment. (of certain nowadays capacitance store can personal classics approachs the level the level of lithium battery, the electric energy that a capacitance stores can use a day for a mobile phone.

 

 

Store can action: Popularly, electroanalysis capacitance can have store can action. To special store can the capacitance of action, capacitance store can mechanism is capacitance of electric double layer and Faraday capacitance, its are main the form is super capacitance store can, among them super capacitor is the capacitor that uses principle of electric double layer, when extra voltage is added to two plate of super capacitor, like common capacitor, the positive electricity of plate extremely memory positive electrical charge, lose plate memory negative electric charge, below the electric field effect that on the two plate of super capacitor charge produces, contrary charge is formed on the interface between electrolyte and electrode, with balancing electrolyte inside electric field, this kind of positive electrical charge and negative electric charge are on the interface between two different photographs, with extremely short clearance is arranged between negative electric charge in contrary locally, this charge distributinging layer is called electric double layer, capacitance is very accordingly big.