Y capacitor connection to chassis is needed in TNYswitch PSU?
Hi,
We are designing a 10W Offline isolated Flyback SMPS.
We wish to use the TNYswitch.
115VAC, 60Hz
24Vout
The SMPS PCB will be suspended in potting in a metal enclosure.
It will have a three wire input, Line, Neutral and Earth.
We have Y capacitors placed from Neutral to Earth_net on the PCB, and from Line to Earth_net on the PCB
, and also across the isolation barrier. The Earth_Net on the PCB then tracks back to the mains input connector where it connects to the earth connection part of the mains input connector.
So, with the PSU on its own, there is actually no connection from the Y capacitors to the PSU's metal enclosure.
The Y capacitors only get connection to the metal enclosure of the PSU when the PSU's metal enclosure is
screwed into the large earthed backplane of the equipment.....and then there is obviously connection of the Y
capacitors to the metal enclosure, going via the earth wire on the SMPS's mains input connector.
Do you think this is a good set-up?
Hi treez,
In a three-wire system, Y-capacitors are connected between chassis ground and Line (L) / Neutral (N). According to studies, this provides a low‑impedance path for high‑frequency common‑mode currents, preventing them from flowing through the LISN resistor during conducted EMI testing.
Your current setup is acceptable, provided the PSU’s metal enclosure is firmly screwed into place as you described, ensuring that the Earth_net has a reliable connection to the chassis.
I hope this helps. Please let me know if you have questions.
Regards,