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How important is PCB Layout -really?

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eem2am

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Hello,

I bought an open-frame 10W SMPS which is a Traco Power TOF10-05S

Its the middle one of the photographs at the top of this datasheet

Datsheet:
http://pdf.dzsc.net.cn/TOF/TOF10-05S.pdf

100-230VAC in,
5V, 2A out,
PCB is 10.5cm by 5cm

Three lead input (Earth, Live & Neutral)

This SMPS works fine.

It looks like a flyback topology, with opto-isolation.

Most of the power components are through-hole.
There are some SMD resistors etc.

It is SINGLE-SIDED in that only the bottom layer has copper on it.

The current loops are definetely NOT as small as they could be.

-the power switch loop is rather large, much larger than it could be.

-In fact you can fairly well see this in the photo on the datasheet...(middle SMPS picture at top)........if you look at the input electrolytic cap......notice which way its leads are.......they are the wrong way.......since if this cap was the other way round the power switch loop would be at least half the size....yet they have not bothered to make this simple optimisation.

The gaps between components look a bit too big.
–Maybe this made it easier to assemble and test.

There is certainly no ground or power plane.

However, this SMPS works fine and passes all EMC test Laws according to its datasheet.

Is it true that the stringent PCB layout rules are in fact rather more strict than they need be.?

I have heard that NO SMPS should be built without a ground plane, but this SMPS certainly does not have one.
 

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