In designs of any switch power source, the physical design of PCB board 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.

 

One, to the design of PCB from principle graph flow establishs component parameter – > input principle net is expressed – > design parameter is installed – > manual layout – > manual wiring – > test and verify is designed – > check – > CAM output.

 

2, span of lead of adjacent of parameter setting photograph 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.

 

3, yuan layout of parts of an apparatus carries 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) , mains switch communicates loop

(Commutate of 2) , output communicates loop

(Loop of electric current of source of signal of 3) , input

(Loop of load current of 4) , output

 

The electric current that input loop sheds 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:

 

•Place transformer

•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