Most propbably of each electronic engineer knows, when the design, PCB design holds very significant position. It is with power source exemple, PCB design can affect ability of noise of the EMC function of power source, output, interference rejection directly, it is basic function even. The PCB wiring of power source part and other hardware have a bit different, how should design? The article uncovers secret for you.

 

Span

To tall voltage the product must want to consider line span. Can satisfy the span that brings compasses demand accordingly best of course, but a lot of moment to needing attestation, or the product that does not have a law to satisfy attestation, span was decided by experience.

 

 

Is much wider span appropriate? Must consider production whether assure the circumstance such as humidity of board face cleanness, environment, other pollution how.

 

To town report input, although can make sure board face is clean, sealed, source of MOS canal leakage is extremely indirect close 600V, be less than 1mm to also compare danger in fact!

 

Board yuan of parts of an apparatus of the brim

In the sticks a capacitance or other easy damage parts of an apparatus of PCB edge, PCB must consider when place cent board direction, if the graph is all sorts of placement when the method, the stress size that parts of an apparatus gets is comparative.

 

Graph the stress that the parts of an apparatus when 1 cent board gets is comparative

 

Can see from this, parts of an apparatus should is far from and parallel at cent board the brim, may divide because of PCB otherwise board cause damage of yuan of parts of an apparatus.

 

Annulus road surface is accumulated

No matter be,be road of annulus of output, power or signal annulus road, should as far as possible small. Power annulus road launchs electromagnetism field, will cause wronger EMI character or bigger output noise; In the meantime, if controlled annulus is received, cause probably unusual.

 

On the other hand, if area of power annulus road is larger, inductance of its equivalent parasitism also can increase, the likelihood increases aiguille of leakage pole noise.

 

The key takes a line

Because of Di/dt action, must reduce dynamic node to be in inductance, can produce stronger electric magnetic field otherwise. If want to reduce inductance, basically be the length that should reduce wiring, add width effect lesser.

 

Line

To whole control part, lv of the take an examination when wiring is far from his power part. If because other limitation is both,lean nearlier, do not answer to run paralell control line and power line, may bring about power source to work otherwise unusual, concussion.

 

Be like control line additionally very long, of a pair of strings that should wind in the future stand by, or get on two faces of both park PCB and to, reduce area of its annulus road thereby, avoid to be disturbed by the electric magnetic field of power part. If pursue 2 showed A, B between 2 o’clock, correct the line wiring method with the mistake.

 

Graph 2 correct the line wiring method with the mistake.

 

Of course, should decrease as far as possible on line use at connective to cross aperture!

 

Spread copper

When having, shop copper is to be done not have completely necessary, should avoid even. If cupreous area is ample big and its voltage changes ceaselessly, on one hand it may serve as aerial, to all round radiation electromagnetic wave; On the other hand it picks up a noise very easily again.

 

Allow to spread copper in static node only normally, carry node of “ ground ” to spread copper to output for example, OK and equivalent increase output electric capacity, filter divides signal of a few noise.

 

Map

To a loop, can undertake spreading copper in the one side of PCB, it is met the wiring according to PCB other one side is automatic map, make the impedance of this loop the smallest. This is like the impedance paralell connection that a group of different impedance are worth, the way with the smallest impedance of can automatic choice has shed electric current same.

 

The one side that can controlling partial circuit in fact undertakes connecting a line, and copper is spread to node of “ ground ” in another, aperture join has been passed between two faces.

 

Output rectification diode

If output commutate diode leaves output end closer, do not answer to place its and output parallel. Otherwise the electric magnetic field that diode place produces will wear power source output and outside the annulus grade that receives load to form, make measures output noise increases.

 

Graph 3 set direction correctly with wrong diode

 

Ground wire

The wiring of ground wire must special caution, cause function of EMS, EMI and other property possibly to become poor otherwise. To the “ ground ” of PCB of switch power source, accomplish at least the following at 2 o’clock:

 

Power ground and signal ground, should only place join;

 

Not due road of existence ground annulus.

 

Y capacitance

Input output receives Y capacitance via regular meeting, sometimes because of certain reason, the likelihood cannot hang his on input capacitance ground, be sure to keep in mind right now, must receive in static node, if high pressure is carried.

 

Other

When PCB of real power source is designed, the likelihood considers even a few otherer problem, for example “ is pressed quick resistor should rely on closely to be protected circuit ” , “ in all modular electric induction increases place of power supply of VCC of chip of discharge tine ” , “ to should increase ceramics capacitance ” to wait a moment. Additional, whether to need special processing, wait like Copper Foil, screen, be in PCB design phase also is need consideration.

 

Often can encounter the situation that many principles conflict each other sometimes, contented among them one cannot be satisfied other, this is need engineer application already some experience, according to actual project demand, decide the most appropriate wiring!

 

Summary

To make the product of tall stability, the design detail that needs in hardware design is very much, the article is the most common power source design in introducing hardware only. To make integral product or system have stable, reliable power supply, major engineer can choose power source module to regard a system as the foundation of power supply.