In design of switch power source the physics of PCB board is designed is the last link, if design method is undeserved, PCB may the electromagnetism interference with overmuch radiate, cause power source to work to be not stabilized, the item that the attention requires in be aimed at each measure below undertakes an analysis:

 

 

Establish component parameter – ” input principle net is expressed – ” design parameter is installed – ” manual layout – ” manual wiring – ” test and verify is designed – ” check – ” CAM output.

 

 

 

Carry out a proof, although design of circuit principle graph is proper, printed circuit board the design is undeserved, also can produce adverse effect to the dependability of electronic equipment. For example, if two fine parallel rely on printed board very nearly, can form the defer of signal weaveform, reflection noise; is formed in the terminal of transmission line the consideration as a result of power source, ground wire is not considerate and the interference that cause, can make the function of the product drops, accordingly, designing printed circuit board when, should notice to use accurate method. Each switch power source has return of 4 electric current:

 

(1) loop of mains switch communication

 

(2) output commutate communicates loop

 

(3) loop of electric current of input signal source

 

(4) loop of output load current inputs loop

 

The electric current that flows continuously approximately through charges to inputting capacitance, filter wave capacitance basically removes a broadband store can action; similar ground, wave capacitance also uses output filter to store the high frequency energy that comes from output commutator, eliminate the dc energy that outputs laden loop at the same time. So, input and the terminal that output filter wave capacitance are very main, input and road of output report regurgitate should part to join from the terminal of filter wave capacitance only if power source; is being inputted / output loop and mains switch / the join between rectification loop cannot as direct as the terminal of capacitance, communicate energy general by input or output filter wave capacitance and radiation goes in the environment.

 

The communication loop of loop of mains switch communication and commutator is included tall an echelon electric current, class status of the harmonic in these electric current is very high, its frequency is ambitious at switch fundamental frequency, peak value extent can be as high as input continuously / 5 times what output extent of dc electric current, bridging time is 50ns about normally.

 

These two loop generate electromagnetism interference the most easily, before because this must be in power source,other prints line wiring first cloth is good these communicate loop, capacitance of 3 kinds of of every loop main component filter wave, mains switch or commutator, inductance or transformer should each other adjacent ground undertakes placement, adjust component position to make the voltaic method between them as far as possible short. The best method that builds position of switch power source is as electric as its the design is similar, optimal design technological process is as follows:

 

 

Design return circuit of mains switch electric current

 

The design outputs loop of rectifier electric current

 

Dominate even what receive circuit of alternating current source circuit

 

Loop of design input current source and loop of load of output of input filter design and output filter basis the function of circuit is unit, to circuit all yuan when parts of an apparatus has position, want to accord with the following principle:

 

(1) should consider PCB dimension size above all. When PCB size is too large, print line to grow, impedance increases, force of the sound energy that fight a confusion of voices drops, cost also raises; is too small to come loose heat is bad, and adjacent line suffers interference easily. The optimal appearance of circuit board is rectangular, length breadth ratio is 3: 2 or 4: 3, be located in yuan of parts of an apparatus of circuit board brim, leave circuit board brim general to not be less than 2mm.

 

(2) when setting parts of an apparatus, should consider the following solder, not too concentrated.

 

(3) it is a center with the core component of every function circuit, will have position around it. Yuan parts of an apparatus should be arranged equably, trimly, compactly go up in PCB, decrease as far as possible and shorten the down-lead between each yuan of parts of an apparatus and join, go the VCC that Ou capacitance stands by parts of an apparatus as far as possible.

 

(4) the circuit that makes in high frequency come off work, want to consider yuan of distributinging parameter between parts of an apparatus. General circuit should make parallel arranges yuan of parts of an apparatus as far as possible. Such, not only beautiful, and outfit solder is easy, easily batch production.

 

(5) the position that plans each functional circuit unit according to the flow of circuit, make layout facilitating signal current, make signal retains consistent way as far as possible.

 

(6) the first principle of layout is to make sure the cloth of wiring is connected rate, the connection of flying line notes when mobile parts of an apparatus, put the parts of an apparatus that has the concern that connect a line together.

 

(7) reduce annulus road area as far as possible, in order to restrain the faze of spoke blackberry lily of switch power source.

 

 

Span of photograph adjacent lead must can contented electric and safe requirement, and produce to facilitate the operation is mixed, span also answer as far as possible some wider. The smallest span wants to be able to suit susceptive voltage at least, when wiring density is inferior, the span of line can be increased appropriately, answer to the line of great disparity of tall, low n as far as possible short and increase span, set span taking a line usually for 8mil.

 

Solder dish inside Kong Bian wants to be more than 1mm along the distance to the side of printed board, solder is brought about when can avoiding to machine so dish be short of caustic. When with solder dish connective goes when the line is fine, should solder dish with walk along the join between the line to design water form, such advantage is solder dish remove a skin not easily, walk along line and solder however dish disconnect not easily.

 

 

The bag in switch power source contains high frequency signal, PCB assumes office why to print a line to be able to have the effect of aerial, the length that prints a line and width can affect its impedance and inductance, affect frequency to answer thereby. Even if pass what shed signal continuously to print a line to also be met from vicinity print line coupling to create circuit problem to radio frequency signal (even again radiation gives interference signal) . Because this answers will all those who carry alternating current print a line to be designed as far as possible short and wide, this is meant must go to all join print line and join to be placed very nearly to yuan of parts of an apparatus of other power supply cord.

 

The length that prints a line and the inductance amount that its show and impedance become direct ratio, and width criterion and the inductance quantity that print a line and impedance become inverse ratio. Length report gives the wavelengh that prints a line to answer, length is longer, print the frequency that the line can be sent and receives electromagnetic wave lower, it can radiation gives more radio frequency energy. According to printed wiring board voltaic size, add as far as possible hire width of power supply cord, reduce annulus road resistance. At the same time, make the direction of the trend of power supply cord, ground wire and electric current consistent, such conducing to enhance power of the sound energy that fight a confusion of voices. Ground connection is switch power source the rock-bottom spur track of loop of 4 electric current, the communal reference point that serves as circuit is having very main effect, it is the important method that controls interference.

 

Accordingly, answer to consider the placement of ground wire carefully in layout, all sorts of ground connection mixture meeting causes power source to work to be not stabilized.

 

1.Right choice sheet nods ground connection normally, the coupling of ground connection dot that public end should be other reachs filter wave electric capacity the exchanges the land only link dot of big electric current, the ground connection dot of same level circuit should be stood by as far as possible, and the capacitance of wave of power source filter of this class circuit also should be received be on dot of this class ground connection, advocate if consider circuit,the electric current that each part circumfluence reachs the ground is change, the impedance of the line that because flow actually,crosses can bring about circuit of potential of each part ground change and introduce interference. In this switch power source, the inductance influence between its wiring and parts of an apparatus is minor, and what ground connection circuit forms is circumfluent bigger to disturbing influence, use a bit ground contact consequently, be about to loop of mains switch electric current (the ground wire of a few medium parts of an apparatus arrives repeatedly on ground connection foot, on the ground connection foot that the ground wire of a few parts of an apparatus that output loop of rectifier electric current receives corresponding filter wave capacitance as much, such power source works are steadier, not easy self-excitation. When making only point, in be located in in all receive two diode or one little resistance, it is OK to receive a Copper Foil that comparing concentration to be in actually.

 

2.If ground wire is very fine,add thick ground wire as far as possible, ground connection potential follows voltaic change and change, the time signal n that causes electronic equipment is flabby, fight noise function addle, because this wants to ensure the ground connection of each big electric current is carried,use quantity weak point and print a line widely, as far as possible width of broaden power source, ground wire, had better be ground wire wider than power supply cord, their relation is: Ground wire ” power supply cord ” line, be like likely, the width of ground wire should be more than 3mm, layer of copper of usable also large area makes ground wire use, join the place that was not used with ground photograph on printed board use as ground wire. When undertaking global wiring, still must follow the following principle:

 

(1) . Wiring direction: Look from solder side, the permutation of component azimuth keeps as consistent as principle graph photograph as far as possible, wiring direction had better walk along line direction photograph to agree with circuit graph, because produce what need to undertake all sorts of parameter in solder side normally in the process to detect, reason makes the inspection in facilitating production so, debug reach the overhaul (note: Below the premise that shows in contented circuit function and installation for complete set of engine and face plate layout ask) .

 

(2) . When wiring pursues, the design takes a line as far as possible little turn a corner, presswork the line on arc is broad not choppy, lead corner should ≥90 is spent, line of do one’s best is understood simply.

 

(3) . In printed circuit not circuit of across of be patient of, to the likelihood alternate line, can get ” , “ to circle ” with “ two kinds of method are solved. The interstitial place “ that lets some down-lead fall from other resistor, capacitance, dynatron foot namely gets ” , or from the likelihood the “ of one aspect of the matter of some down-lead of across circles ” past, fall in special situation how circuit is very complex, to simplify the design also allows to use lead bond, solve alternate circuit problem. Because use odd face plate, insert component to be located in Top face continuously, the watch sticks parts of an apparatus to be located in Bottom face, be in so layout when insert parts of an apparatus to be able to stick parts of an apparatus to hand in with the watch continuously fold, but should avoid solder dish jackknife.

 

3. input ground and output ground are low-pressure DC-DC in this switch power source, what be about to answer output voltage feedback transformer is primary, the referenced ground with the due and common circuit of both sides, after spreading copper respectively to the ground wire of both sides so, join together even, form common ground.

 

 

After wiring design is finished, need to check wiring design to whether accord with the regulation that architect place drafts seriously, whether does the regulation that also needs to affirm place is made at the same time accord with printed board to produce the demand of craft, general examination line and line, line and component solder dish, solder of line and aperture of be well versed in, component dish as reasonable as the distance between aperture of aperture of be well versed in, be well versed in and aperture of be well versed in, whether to satisfy manufacturing requirement. The width of power supply cord and ground wire is appropriate, whether is there still the place that can let ground wire broaden in PCB. Attention: Some mistakes are negligible, the one share that has some of Outline that receives plug-in unit for example is put outside board casing, the meeting when checking span makes mistake; has been revised every time additionally go line and after crossing Kong Zhi, want new Fu copper.

 

Content includes to design regulation, layer definition, line wide, span, solder dish, setting crossing aperture, check mainly even the rationality of layout of parts of an apparatus, of network of power source, ground wire take a line, of network of high speed clock take line and screen, go of Ou capacitance put and join.

 

The design outputs the note that outputs smooth draw file:

 

A. The layer that needs output has wiring layer (rock-bottom) , silk imprints layer (include to carry a silk on the head to imprint, rock-bottom silk imprints) , block solder layer (rock-bottom block solder) , bore layer (rock-bottom) , make bore file even additionally (NC Drill)

 

B. Setting silk imprints when the Layer of the layer, do not choose Part Type, the choice carries a layer on the head (rock-bottom) imprint with silk the Outline of the layer, Text, Linec. When installing every Layer, choose Board Outline on, setting silk imprints when the Layer of the layer, do not choose Part Type, the choice carries a layer on the head (rock-bottom) imprint with silk the Outline of the layer, Text, Line. D. When making bore file, the default of use PowerPCB is installed, do not make any changing.