Common ground

I need three different voltages from a power supply, 30V unregulated, 12V for peripherals and 5V for the MCU.

In order to save one transformer (PCB size is an issue) I intend to use the entire secondary winding of the transformer for the 30V part, and one outer tap and the center tap for 15V (regulated 12V).

I've never done that before.

Will there be any problems connecting ground terminals for common ground?

Boncuk

You don't need the 1st bridge rectifier at all:

I agree with kchriste.
The diodes marked a&b always conduct on the + 1/2 cycles and diodes c&d always conduct on the - 1/2 cycles so the center tap is always a + voltage.

Thanks a lot,

that makes the PCB even smaller.

Boncuk