mtwieg
Advanced Member level 6
I'm starting a medical PSU project (~1kW), low leakage and low EMI are critical. I planned to address this by using faraday screens in the DC-DC transformer, in order to reduce or eliminate the Y capacitor between primary and secondary.
The one thing I'm stuck on is how the use of the shields affects the my insulation category and creepage distance. Normally, without any faraday shields, you can just use appropriately rated triple insulated wire and be done. But if the screen(s) are put between the windings, then I expect that it would eliminate the protection gain from the TIW, assuming the shield connects directly back to the primary or secondary circuit ground. So does that mean there's no point in using TIW with a shield?
What if the shield is connected to the circuit ground via a ~10nF Y capacitor (rated for the working insulation voltage)? Could the shield then not be considered an issue for insulation failure, since it's effectively an open circuit at 50/60Hz? I've seen this trick mentioned in a couple texts, but can't find any reference to it in IEC 60950 or IEC 60601-1.
The one thing I'm stuck on is how the use of the shields affects the my insulation category and creepage distance. Normally, without any faraday shields, you can just use appropriately rated triple insulated wire and be done. But if the screen(s) are put between the windings, then I expect that it would eliminate the protection gain from the TIW, assuming the shield connects directly back to the primary or secondary circuit ground. So does that mean there's no point in using TIW with a shield?
What if the shield is connected to the circuit ground via a ~10nF Y capacitor (rated for the working insulation voltage)? Could the shield then not be considered an issue for insulation failure, since it's effectively an open circuit at 50/60Hz? I've seen this trick mentioned in a couple texts, but can't find any reference to it in IEC 60950 or IEC 60601-1.