Earth ground for safety or electrical noise?

[eem2am]

electrical earth ground

Hello,

In offline SMPS the earth connection is often taken onto the SMPS PCB.

Now i wonder. -Is the Earth ground solely for Electrical Safety or is it also for helping to filter noise away ?

-Since the common mode filters always seem to be filtering the noise away to earth ground ?

 

[flatulent]

safety in electrical grounding

It is for safety. There are detailed government laws about how it is to be done that you have to follow.

 

[FvM]

electrical noise dangerous

Both reasons play a role. Basically, you can design SMPS with safety isolation that don't need a protective ground connection. Most small off-mains SMPS are designed this way. Unfortuanately, they typically need capacitors accross the isolation barrier to comply with EMC regulations. They cause an AC leakage current respectively an AC voltage of 1/2 mains voltage at the floating DC output, that is unwanted and may even damage sensitive electronic equipment.

SMPS with a protective ground can also use it to connect the secondary Y-capacitors or an optional screen winding, avoiding AC leakage currents.

 

[eem2am]

earthing mains voltage safety

Thankyou Flatulent & FvM for answers.

FvM, So basically from what you say i believe it is indeed best to have an earth ground connection at the secondary 0V, or else my secondary willl float at this dangerous (half mains) voltage, and indeed the secondary circuitry would be dangerous to touch ?

So i conclude that an earth ground is not necessary for filtering away noise, but when i do filter away noise, i really end up needing an Earth Ground for safety reasons ?