to pass EMC test, simply add more filtration ?

[eem2am]

Hello,

If an SMPS fails the conducted EMC test, it could be due to the layout being rather poor.

Poor layout would result in common mode noise.

Supposing there was no room to lay out the components in a better fashion….

--then am I right in saying that passing the EMC test is just a matter of adding more common mode chokes to the inputs and outputs , until the EMC test is passed?

 

[dipnirvana]

Not always Common mode noise , some time differential noise, too will create problem for bad layouting depending on wattage of ur SMPS.

So think of DM filter too, along with CM filter.

 

[eem2am]

thankyou dipnivana, but do you agree with me it is more a common mode noise causation?

agreed there is some diff mode effect but we are mainly talking common mode?

 

[cristivasilache]

when you perform an EMC test, they have to point-out the values and result of the test. is not just simply pass/fail test. havin the results you can have an ideea what kind of noise do you have, and locate the source of the noise. there is conducted, and radiated noise. you said that you have problems with conducted noise. simply adding more capacitors or increasing the inductances may not solve the problem. what is the noise spectrum ? think about the parasitics which you can eliminate without redesigning the board, such as drain to GND capacitance due to improper heatsinkin or flux leakage of the transfomer which doesn't have copper shield arround. keep in mind the resonace of the filter elemnets when you choose their values !!!

 

[elexlearner]

eem2am,

It depends on the type of spectrum (in Conducted emission test).
Generally, its the differential noise that is substantial in lower side of the spectrum i.e till 1mhz or so but as we move on it is the common mode noise that is really crutial. If you are getting the problem in higher frequencies, think of the parasitic Capacitances.


So it can be one of the area which can give u the direction