I am working on a board that contains a DC stage, an SBC module, mechanical relays (smd) and communication modules. The power supply is a cheap 24v AC-DC converter. It is a COTS product. The DC stage needs to provide a 12v, 5v and 3.3v.
I need to supply different kinds of systems simultaneously: communication modules (wifi, ethernet, cell, usb), an external tablet, an SBC, multiple ATtinys, RS422 drivers, sensors and other peripherals.
As I see it, the DC design is key both from power requirements of the board and also from EMI and noise suppression.
The previous version of the board was designed poorly in terms of schematic and layout.
- Design a converter for the 24V to 12V drop.
- Use a linear regulator (non LDO) to step the 12V to 5V.
- Use an LDO to regulate the 5v to 3.3V.
My design guidelines are, of course, open for input.
My questions are:
what kind of converter should I choose? will a flyback be sufficient?
Can I trust a switched converter to supply communication modules and controllers?
If I use a non-isolated converter (24V to 12V), will separating the grounds (analog, digital) help me suppress interferences on my PCB? Are there other methods I should implement?
Should I place the DC stage on one small area on the board or put the regulators as close as I can to their relevant consumers?
If I don't have size constraints, is it better to lay out in two layers or four?
I'd welcome other inputs and reading references (links, pdfs...) :)
Many thanks for your help!