It is good practice to either earth the 0v output - as long as it is labelled so..!! or put a 1W, 1Mohm res from earth to 0v o/p
Thanks, I forgot to do this on our 60W SMPS prototype due to rushing. We do have an Earth connection to the PCB…therefore, for the EMC test, I will just have to have a wired connection from the Earth connection on the primary side…..over to the secondary 0V. I will make sure it won’t chafe on the components.
Incidentally, which do you think would give the better EMC scan…….using a direct connection of the secondary 0V to Earth…or connecting secondary 0V to Earth via a 1Meg resistor?
I presume the latter would be better since it reduces the propensity for common mode noise to avoid the Mains input common mode filter(?)
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Hello,
We have just hurriedly designed and built a 60W offline Flyback LED driver for a demo at a show. It’s now working well.
We have booked in for Conducted and Radiated EMC scan as we don’t have the EMC test kit.
(However, in my haste, I forgot to add a 1Meg resistor from Earth to secondary 0V on the PCB).
As such we will have to EMC test it with the secondary output just floating.
In the real application, the secondary output will have a DALI radio module connected to it, and the 0V of this radio module is Earthed. As such, in the real application, the secondary of our 60W offline Flyback will be earthed. This obviously means that the conducted EMC test test results regarding common mode noise would be worse in the real application, as common mode noise can flow to earth via the secondary without having to go through the common mode filter of our 60w offline flyback PCB.
Anyway,
supposing we do Conducted EMC testing on our 60W Flyback without the DALI radio module connected, and with its output just just floating and powering the LEDs….then does this give us a valid EMC pass?.......ie, is it valid to test it without the secondary being Earthed? (it will be Earthed in the real application).