Author Topic: Copper Pour questions with Isolated DC-to-DC encapsulated SMPS design  (Read 179 times)

0 Members and 1 Guest are viewing this topic.

Offline K3mHtH

  • Regular Contributor
  • *
  • Posts: 70
  • Country: ca
Hey everyone,
I'm designing a PCB for a little CUI encapsulated isolated DC-to-DC power supply (+/-15V) and looking for some tips regarding the copper pour. My "ground" connection is currently on the load side.. I'm worried that having this as the copper pour across the board, underneath inductors and the SMPS might induce switching noise into my ground?

Clearly I'm a bit over my head here, and just looking for some general advice.

Here is the DC-to-DC I'm using: https://www.cui.com/product/resource/pdqe15-d.pdf
My circuit is copied from Page 6, Figure 4.
 

Offline T3sl4co1l

  • Super Contributor
  • ***
  • Posts: 17188
  • Country: us
  • Expert, Analog Electronics, PCB Layout, EMC
    • Seven Transistor Labs
What are you isolating?  Are there conducted or radiated paths from both sides (ground/earth connections, connectors/cables, etc.)?

Note that those things are tested basically alone, no common mode data.  Expect to need an external CMC if you need it quiet.

And how much noise can you tolerate?  Functional or regulatory..?

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline K3mHtH

  • Regular Contributor
  • *
  • Posts: 70
  • Country: ca
The input is isolated from the output, to avoid possible ground loops - this is in an audio device.

The PSU is on a separate PCB with a 3 pin connection leaving it (for +15, GND, and -15). There is also a 2 pin connector for a power LED, powered off the -15V.

I currently have a common mode choke on the input, since I noticed it made things a lot less noisy during my breadboard testing with an oscilloscope.

Basically I'm just wondering what best practices are for ground planes, if there should or shouldn't be any - especially under the CMC, inductors and DC-to-DC itself. And what that ground plane should be connected to (unconnected, input voltage ground (before or after CMC), output voltage ground, etc.). I hope that helps.



 

Offline K3mHtH

  • Regular Contributor
  • *
  • Posts: 70
  • Country: ca
Here's a schematic if that helps.

There is a +15/-15V supply that goes to internal audio components. The 9V output goes to external stuff, where some stuff can be connected as -9V with the + rail being grounded.

 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf