Non isolated 30W offline LED driver and common mode noise filtering

[treez]

Hi
We are doing a non-isolated, offline, 30W PFC Boost-Buck LED driver.
In order to get better filtering of common mode emissions, would you say it is preferable for us to take an earth wire to the PCB? (then we can also use Y capacitors to earth, as well as a common mode choke)

 

[ArakelTheDragon]

This is a hard topic, I suggest you test with care!

 

[wwfeldman]

in 20 years at two power converter manufacturer, i never saw a connection to earth as you describe.
not a good plan

 

[treez]

Thanks, but LC filtering common mode noise is surely more attenuative of it than common mode inductance alone?

 

[asdf44]

in 20 years at two power converter manufacturer, i never saw a connection to earth as you describe.
not a good plan

Huh? You've never seen a common mode choke combined with C to earth?

 

[wwfeldman]

common mode chokes, C line to line and line to neutral, but not neutral to earth

copper cables chassis to earth but not pcb to earth

 

[mtwieg]

C line to line and line to neutra

For US mains (single phase 120Vac), "line to line," "line to neutral," and "line to hot" are all equivalent. Are you thinking of a split phase system?

 

[wwfeldman]

three phase
delta gets line to line
wye gets line to neutral

 

[Easy peasy]

CM chokes with no earth will work - but often a test spec calls for metal foil pressed against device ( which is connected to Earth ) thus introducing C to earth - then the measurements are taken at the LISN - thus a very good wide band CM choke is needed to pass this test ...