Y cap not connected between "quiet nodes"?

[cupoftea]

Hi Page 7 of the below, shows Y cap connected from Primary "quiet" node to a "quiet node" on the sec , but the sec node is not directly connected to the transformer....so why didnt they connect the y cap from primary +HV, to secondary centre tap...because the centre tap is not a switching node, (so its suitable "quiet") and is directly connected to the transformer.

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72 W isolated flyback power supply for compact chargers and adapters using PowiGaN-based InnoSwitch3-CP (INN3279CH215)

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[Easy peasy]

it is connected via the caps in the ckt nearby

 

[cupoftea]

Thanks, yes, but that means the connection is via the stray L and R of that 330uF 25V Electrolytic capacitor, plus the stray L of the PCB traces involved.......surely a direct connection of the Y cap would have been better, and could just as easily have been done.

 

[mtwieg]

Unclear what you mean by a "quiet" node. Quiet relative to what? No earth connection is indicated on the schematic, so it's somewhat arbitrary.

I would guess that C3 would function approximately the same if it was connected to the other side of the bridge rectifier, or if it connected to the +36V output, or TX center tap. It's likely they tried all combinations and chose this one because it gave a slightly better EMC result overall.

 

[cupoftea]

Quiet node meaning not like a switching node, eg not like the drain node.
As you know, Neutral is earthed somewhere so there is effective earthing.