Is placing 4 little switching power supplies (3.3V, 5V, +9/-9V) on 1 board to share the same ground a bad idea?

And how should I place the inductors?

https://encrypted-tbn0.gstatic.com/...45ycTPLoV8IdpL_VXSG2ltu49LHghbEsUHyKvkAYZiRFT

this is the inductor shape

 

Hmm.. What topology? I don't get it :/

 

You can put all four power supplies on the same board if you are careful about layout and decoupling.

The common ground should be a continuous PCB ground plane covering the whole PCB area.

Each supply should have it's own input decoupling capacitor.

The input decoupling capacitor, MOSFET switch, free-wheeling diode, and output inductor should be connected as close together as possible to minimize the distance the current must flow between these devices.

 

You can put all four power supplies on the same board if you are careful about layout and decoupling.

The common ground should be a continuous PCB ground plane covering the whole PCB area.

Each supply should have it's own input decoupling capacitor.

The input decoupling capacitor, MOSFET switch, free-wheeling diode, and output inductor should be connected as close together as possible to minimize the distance the current must flow between these devices.

yep and everything else in the "PCB layout" suggestion section of the datasheets..

making it for a diy project is one thing..needing that board to meet FCC/EMI/EMC testing is another..

 

You can put all four power supplies on the same board if you are careful about layout and decoupling.

The common ground should be a continuous PCB ground plane covering the whole PCB area.

Each supply should have it's own input decoupling capacitor.

The input decoupling capacitor, MOSFET switch, free-wheeling diode, and output inductor should be connected as close together as possible to minimize the distance the current must flow between these devices.

Thanks... And inductor position, should I just place them as far as possible from each other, or I have to change their orientation, rotate them and stuff?

 

i would just build one regulated smps with feedback adjusted to monitor your highest voltage and using fixed regs to suit

You do know that a 3.3V linear supply, driven by 9V has, at best, 37% efficiency, yes?

And, assuming the 3.3V supply is at a higher current than the 9V supply (a generally safe assumption), the 9V supply would have to be overdesigned to not only handle the 9V circuit current consumption, but that of the 3.3V circuit as well?

What you might do may not be best for the OP's application.