For a delicate application I need less than 100pF between secondary and mains ground.
I would be glad if someone could steer me in the right direction how to achieve this.
Thx in advance
Hans
I would be glad if someone could steer me in the right direction how to achieve this.
Thx in advance
Hans
IMO primary-secondary capacitance is much more important.
Most of noise from the mains spreads through it.
Two bobbin/splitted bobbin transformers has enough low p-s capacitance.
Shielding (tape or one layer wire between primary and secondary) also gives a good result.
Most of noise from the mains spreads through it.
Two bobbin/splitted bobbin transformers has enough low p-s capacitance.
Shielding (tape or one layer wire between primary and secondary) also gives a good result.
Hans, I have a similar requirement for my eDD NextGen design, but I also need 5kV isolation between prim and sec.
I spoke with Menno van der Veen and it's a tough target. It can easily be more than a nano-Farad.
You could talk to him.
At any rate, it will come with very much reduced efficiency.
Jan
I spoke with Menno van der Veen and it's a tough target. It can easily be more than a nano-Farad.
You could talk to him.
At any rate, it will come with very much reduced efficiency.
Jan
Yes, that’s the capacity I’m referring to.
Do you mean two Transformers one after the other, both with EI cores and each having two separate bobbins ?
Hans
No.
I thought such transformer, when primary part and secondary part are separated:
1.) separated bobbins for pri and sec on the far legs of EI transformer;
2.) or splitted bobbin, when primary and secondary are in separated bobbin part.
I prefer the latter.
Sample:
https://www.reichelt.de/de/en/mains...86a52bb061f180924cf94a811132&LANGUAGE=EN&&r=1
The R-core may not help anyway. At least it will depend on how the transformer is made.
I just made a quick measurement on an R-core transformer I have. It measured something like 110pF between primary and secondaries. It was a different transformer with 2 x 15V and 2 x 9V secondaries.
But I think that the primary is split between the two bobbins and the same for the secondaries, probably to get a good coupling/regulation. For lowest capacitance the primary should be on one bobbin and the secondary on the other one. This will probably sacrifice some of the coupling, but I think the capacitance should be lower.
I just made a quick measurement on an R-core transformer I have. It measured something like 110pF between primary and secondaries. It was a different transformer with 2 x 15V and 2 x 9V secondaries.
But I think that the primary is split between the two bobbins and the same for the secondaries, probably to get a good coupling/regulation. For lowest capacitance the primary should be on one bobbin and the secondary on the other one. This will probably sacrifice some of the coupling, but I think the capacitance should be lower.