No,Whatever the reason for the caps they pretty well defeat the usual reasons for having an isolated supply.
I was referring to DC-DC converters which the OP's device appears to be, not line-powered AC-DC supplies.No,
There is no DC path from input to output. A inductor would defeat isolation.
All AC to DC swithing power supplies have a capacitor from primary to secondary. 1000pF 1kv, power line rated. You have to have this to get noise rating.
Not necesasry all switching suplies, but most of them. It is possible to make small power converters without it and still pass EMC regulations, but it is complicated and mostly trial and error to get the supply right.All AC to DC swithing power supplies have a capacitor from primary to secondary. 1000pF 1kv, power line rated. You have to have this to get noise rating. See C4 below.
I was to but compared to AC to DC because many people seen the filter caps there.I was referring to DC-DC converters
You will be hard pressed to find one. Even the power supplies for high end test equipment has these capacitors. I design transformeres that have low primary to secondary capacitance and noise cancelling windings and I still add the caps.It is possible to make small power converters
Yes, There is noise from the transformer and I am trying to return the noise back to the source and not let it get into your loop. With out the cap the sharp edges on the MOSFET/Diodes will push through the 100s or 1000s of pF in the transformer and the noise will pound your isolated supply.capacitors gives you an AC loop
ThksThe screen helps!
The two red capacitors I added in post #10 are part of the transformer and not added to the PCB. The two caps in #5 are on the PCB.
If you have one screen: There is a primary-winding capacitor to screen. Also there is a secondary-winding capacitor to screen. Then where do you connect the screen. Some times there are two screens. One connected to primary ground and one connected to secondary ground. There will be a huge capacitor made inside the transformer (screen1 to screen2).
Can you explain this?I have had good luck making a cancellation winding.
I was talking about a layer of copper between primary and secondary. Usually 1.25 turns. Not connected so current flows. Usually connected to P or S ground. It is a shield against electrostatic noise. Not magnetic noise.When you say screen you mean a magnetic screen
What noise:cancellation winding