I am designing a circuit where there is a need of different power sources
3.3V(for micro SD card level shifter),
5V(micro controller unit),
15V (Fet Drivers).
Is there any way(any circuit or any idea to develop one) so that we can reduce the no. of power sources in the overall design?
I dont understand. If you need three supply voltages you need to generate them.
Either you need 3.3V or not.
If you need it you will have to generate this 3.3V.
You may use
* Linear regulators (reducing voltage only)
* step down switching with inductor
* step up switching with inductor
* capacitive switching
You may use a flyback topology with multiple output voltages.
Or you use a ready to buy supply.
Doesn´t an ATX PC power supply generate all three voltages? (Just saw it generates 12V instead of 15V, but maybe also good for a FET driver)
Another idea: using FETs which can be driven from 5V.
Odious obvious remark: It would help to know what the supply(ies)/source(s) will be. Without that information, maybe a dual LDO, and I'm certain that 5V and 3.3V are abundant as those are such standard voltages. The Fet driver, maybe a switcher, as Klaus already said (and feed the dual LDO from it's filtered output...).