cupoftea
Advanced Member level 6
Hi,
We have a large board, 150mm by 100mm. It has a 20w offline isolated flyback on it and
some general analog circuitry on the isolated secondary side. There is also, another
small section which is again isolated from both mains and from the main isolated section.
A digital isolator communicates to this from the main isolated section.
This smaller isolated section has a terminal
block through which it receives its low power supply from another isolated offline smps on another board.
The board is in an earthed metal enclosure. There are y caps from L->E and N->E, and from Sec+_->E and from SEC-_->E.
(also a Y1 across the isolation transformer barrier).
The board is very expensive, and as is well known, really the entire secondary circuit area needs to be y capacitor connected
to earth. -But this would mean too many y caps. However, there is a 2mm thick earth "wall" which traverses the entire
PCB, (just lying on top of it, not actually formally affixed to it) and I am just thinking,
we could add some sec ground copper tracking right underneath it, (under suitable insulator) which
effectively puts a nice , extensive (albeit stray) Y cap over the whole secondary side.
Would you agree this is a good idea for EMC reasons?
We have a large board, 150mm by 100mm. It has a 20w offline isolated flyback on it and
some general analog circuitry on the isolated secondary side. There is also, another
small section which is again isolated from both mains and from the main isolated section.
A digital isolator communicates to this from the main isolated section.
This smaller isolated section has a terminal
block through which it receives its low power supply from another isolated offline smps on another board.
The board is in an earthed metal enclosure. There are y caps from L->E and N->E, and from Sec+_->E and from SEC-_->E.
(also a Y1 across the isolation transformer barrier).
The board is very expensive, and as is well known, really the entire secondary circuit area needs to be y capacitor connected
to earth. -But this would mean too many y caps. However, there is a 2mm thick earth "wall" which traverses the entire
PCB, (just lying on top of it, not actually formally affixed to it) and I am just thinking,
we could add some sec ground copper tracking right underneath it, (under suitable insulator) which
effectively puts a nice , extensive (albeit stray) Y cap over the whole secondary side.
Would you agree this is a good idea for EMC reasons?
Last edited:
