Capacitance is in actual circuit type selecting skill
[introduction] the application of voltage of extremely low to needing to be changed from tall input voltage output, have different solution. An interesting example is change 3.3 V from 48 V. Such norms is not only in the server application of IT market very common, likewise common in telecommunication application.
Capacitance is the passive parts of an apparatus that we often use in circuit, via a few kinds when often see aluminium electroanalysises capacitance, filter wave capacitance, tantalum capacitance, stick a capacitance of pottery and porcelain to wait. Because the character of every kinds of capacitance decided corresponding use situation is different. So the article introduces the ABC of capacitance first, pass the distinction that compares a few kinds of capacitance and characteristic next, summary went out to choose the skill of capacitance in actual circuit.
The ABC of capacitance
The classification of 1. capacitance and action
Capacitance by two metallic pole, intermediate clip has insulating material (medium) form. As a result of insulating material different, the sort of the capacitor that makes also differs somewhat:
(1) can divide by the structure for: Secure capacitance, alterable capacitance, fine tuning capacitance.
(2) can divide by medium material for: Aeriform medium capacitance, liquid medium capacitance, capacitance of inorganic solid medium, capacitance of organic solid medium electroanalysises capacitance.
(3) by polarity cent is: Have polarity capacitance and without polarity capacitance. We are the commonnest those who arrive is to electroanalysis capacitance.
(4) capacitance has partition dc in circuit, carry the action of alternating current.
The symbol of 2. capacitance
The symbol of capacitance divides notation of the internal standard that it is a country and notation of international electron symbol likewise, but capacitance symbol expresses in home and international about the same, exclusive distinction is in namely polarity capacitance goes up, domestic is an empty basket below a horizontal line, and international is common capacitance add symbol of a “+” to represent positive electrode.
In circuit graphic representation, capacitance marks with C symbol commonly.
The unit of 3. capacitance
The main unit of resistor is: F (law) , still have μF in addition (small way) , NF (accept law) , PF (leather law) , because the size of capacitance F is very large, what so we see is general it is μF, NF, PF, is not F. The specific conversion between them is as follows:
1F=1000000μF
1μF=1000nF=1000000pF
The compression unit of 4. capacitance: V (volt)
Each capacitance has its compression value, this is one of important parameter of capacitance. Common those who do not have polarity capacitance is nominal compression value has: 63V, 100V, 160V, 250V, 400V, 600V, 1000V, the compression value that has polarity electric capacity should compare the compression that does not have polarity capacitance to want relatively low, general nominal compression value has: 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 220V, 400V.
The sort of 5. capacitance
The sort of capacitance has a lot of, can be from the cent on the principle: Without polarity alterable capacitance, secure capacitance without polarity, polarity capacitance waits, can divide from material for: CBB capacitance (polyethylene) , polyester fibber capacitance, ceramics capacitance, micaceous capacitance, alone stone capacitance, electroanalysis capacitance, tantalum capacitance.
The skill that the capacitance in circuit chooses
Had the capacitance ABC above to make bedding, we compare the distinction of a few kinds of capacitance and characteristic below, sum up a few skill that choose capacitance in actual circuit.
(1) aluminium electroanalysises capacitance. Its main component is aluminum foil and electrolyte. Simple understanding aluminium electroanalysises the manufacturing technology of capacitance, namely aluminum foil roll into columnar, electrolyte of infuse liquid state, again derivative losing two terminal, next the core material capacitance is sealed in metallic crust. The presence in liquid state electrolyte is constant proportional water, below the case that there should be leakage current to had flowed on capacitance, water can be decomposed to be hydric with oxygen, oxygen passes oxidation reaction to be able to form new oxidation film with positive pole, hydric the rubber stopper eduction that passes capacitance. Capacitance of so unapt attaint. Manufacturing technology is simple, cost is low it is aluminium electroanalysises a characteristic of capacitance. Besides, aluminium electroanalysises capacitance still has the following characteristic:
A. Because sealed carapace is not complete sealed, electrolyte can dry up easily, because this aluminium electroanalysises the service life of capacitance is finite;
B. As a result of the existence of the water in electrolyte, affected aluminium to electroanalysis the performance characteristics that capacitance issues in high temperature and microtherm environment;
C. Craft character reason, aluminium electroanalysises the ESR of capacitance, ESL is done harder small, because this aluminium electroanalysises,compare of capacitance normally from syntonic frequency dot low, arrive in a few KHz roughly limits of a few MHz;
D. Aluminium electroanalysises the dimension positive of the capacity of capacitance and aluminum foil closes, what the capacity can do is very big, dimension of larger electric capacity exceeds the capacity big.
According to above character, aluminium electroanalysises the filter wave occasion that capacitance is used extensively in low frequency, arrive in a few KHz especially the environment of a few MHz, for instance the output filter wave of power source, what we often see is aluminium electroanalysises the form of capacitance. Electroanalysis in use aluminium capacitance when, want to notice capacitance compression satisfies circuit requirement. Additional, in other requirement not severe case falls, the capacity can choose as far as possible a few bigger, the size is larger ESR is smaller, satisfy the requirement of circuit target impedance more easily. The environment is used in certain high temperature, the aluminium that avoids to choose minor volume small size as far as possible electroanalysises capacitance, lest because temperature crosses tall electrolyte,volatilize,dry up the job that creates capacitance invalidation to affect whole circuit.
(2) filter wave capacitance. The capacitor capacity that uses as a result of filter wave after rectification is larger, reason must be used electroanalysis capacitance. Filter wave capacitance is used at power amplifier, its value should be 10000μF above, use at preamplifier, the capacity is controlled for 1000μF can. When circuit of wave of power source filter direct supply amplifier works when, its capacity jumps over great acoustic quality to had been jumped over. The electric capacity that Dan Darong estimates will make impedance from begin to rise near 10KHz. Should adopt paralell connection of a few a bit small electric capacity to also answer at the same time into large electric capacity at this moment shunt-wound a few filmy capacitance, beside large electric capacity in order to restrain the rise of high frequency impedance. The characteristic of filter wave capacitance includes the following fields:
A. Harmonic filter loop is comprised by reactor of capacitor series connection, in some harmonic rank second form lowermost impedance, in order to absorbs many harmonic electric current, the quality of capacitor can affect the stability of harmonic filter to absorb the effect, the service life of capacitor has very big concern with temperature, temperature is higher life is lower, capacitor of filter wave complete film has temperature rise low characteristic, can assure its service life;
B. Loss is small, tangent of dielectric loss horn is worth (Tgδ ) : ≤0.0003;
C. Accord with standard of GB, IEC, in-house monomer capacitor all is added install protector;
D. Volume is minor and weight is light, carry installation very convenient.
It is shunt-wound that according to the characteristic of filter wave capacitance we can understand filter wave electric capacity end is outputted in circuit of rectification power source, in order to reduces a kind when communicate output of pulsatile and moire coefficient, flowing dc store can parts of an apparatus. In using the electronic circuit that is communication changeover dc power supply, filter wave capacitance makes output of power source dc smooth not only, reduced hand in become pulsatile and moire to be opposite the influence of electronic circuit, the interference that the voltaic wave motion that still can draw the generation in process of electronic circuit job at the same time and by alternating current source string together, make the character of service of electronic circuit more stable.
(3) tantalum capacitance. Tantalum capacitance is additionally one kind uses extensive electric capacity, electroanalysis with aluminium capacitance is same, tantalum capacitance also is one kind electroanalysises capacitance. Its main technological process is the agglomeration after tantalum pink suppress shapes becomes poriferous sincere piece, form oxidation film through in relief poling, next clothe solid electrolyte, again clothe a black lead and plumbic stannum coating, enclose with colophony finally shape the tantalum capacitance that is solid. Tantalum capacitance has following characteristics:
A. Electroanalysis with aluminium capacitance is different, the electrolyte of tantalum capacitance is solid, the problem that so nonexistent electrolyte dries up, life can rise somewhat;
B. As a result of adoption solid electrolyte, character of its capacity temperature is stabler, because this temperature is right the influence of capacitance capacity is minor, aluminium of excel of function of high low temperature electroanalysises capacitance;
C. Tantalum electroanalysises capacitance can be accomplished relatively enclose lesserly below high capacity, because of this ESR, ESL is OK pilot is younger, its electroanalysis than aluminium from syntonic frequency capacitance wants tall;
D. Electroanalysis than aluminium on craft capacitance is complex, cost is higher.
Through comparing us to be able to discover, tantalum capacitance has a lot of aluminium to electroanalysis the advantage that capacitance does not have, aluminium can be replaced very well to electroanalysis in the capacitance of use setting Tantalum of certain strain wave capacitance. But the place that has attention of a few need: Because the structure of tantalum capacitance decided, the compression of tantalum capacitance is general not tall, in actual circuit the compression of capacitance of serious attention Tantalum asks, stay have certain surplus. Coping with instant of power source electrify to big electric current is pounded and change with great voltage very short time respect Tantalum capacitance electroanalysises without aluminium capacitance is outstanding. Temperature is very small to the influence of tantalum capacitance, we are negligible in be being used actually the temperature influence to tantalum capacitance.
(4) ceramics capacitance. Ceramics capacitance is we use most electric capacity in actual circuit, its structure is simpler, fold agglomeration together alternately and become ceramics namely. Bulk small cost is low, use extensive. Its want a characteristic to have only:
A. Size is small. Ceramics capacitance structure is simple, dimension can be accomplished very small, 0402 even 0201 enclosed ceramics capacitance apply extensively in the situation that has firm demand to dimension so like the mobile phone;
B. Electric performance is steady, temperature influence is minor;
C. ESR, ESL cost is very low, from syntonic frequency taller, applicable asks to the filter wave of 1GHz at on PCB a few MHz;
D. Because multilayer structural character is mixed,enclose a reason, resistance curves ability poorer, PCB bends be out of shape cause capacitance craze invalidation likely.
According to character of above parts of an apparatus, ceramics capacitance besides application at filter wave setting beyond, apply extensively still at lying between straight, coupling, a variety of application circumstances such as bypass. Its job frequency relatively electroanalysis capacitance has very big rise, can satisfy a few MHz to the applied environment of 1GHz.