What I try to build
I'm building a tiny class-d amplifier with an Arduino Nano as MCU, tiny OLED display (logo, selection info, Volume info, VU-meters), 3 buttons (input selection, volume) and a bluetooth module (and soundcard but not integrated yet because of the following problem). It all fits inside a candy case (82mm x 55mm) of throat sweets called Wybert ;-) .
The setup is pretty straightforward, there are two transistors (1020Y) controlled by the arduino that enables/disables resources, this is working fine. Only when I enable the bluetooth there is a terrible noise (data noise) because of a ground loop, everything shares the same ground. This can be solved with an isolated DC/DC converter (see this video: https://www.youtube.com/watch?v=b2Pb1KuVDS0 ). 1W is enough because the whole setup consumes only 90mA at max (arduino, screen and module when everything is switched on).
Why I need it
There is 'enough' 'room' (pretty tight actually) to implement this isolated DC/DC converter but the amplifier can run on 5VDC (2x3.5W min) to 24VDC (2x50W max). When I need a DC/DC converter, why not combine the two, a regulator like a car usb charger for example (can be very tiny also, have one, but not isolated). You can input max 24V or less to get 5V. I know normally a DC/DC step-down converter that outputs 5V needs more than 5V but the component I'm talking about is a 5VDC to 5VDC converter. It must be possible to have smart component that always outputs 5V in a range between 5V and 24V or am I wrong?
What I want to avoid
What I want to avoid is two DC/DC converters when powered on a battery (12V-24V) for example, that will be very inefficient and can introduce allot of trouble. In this case I need two powerlines that provide 5V (for the isolated DC/DC converter) and the 12-24V range for the amplifier. So when I can combine the two, I need only one powerline to power the whole device, you can input everything between 5V and 24V.
Allot of flavours
There are allot of isolated DC/DC converters but I see only with fixed input or cannot figure out if it is possible to input a lower voltage (sometimes a min range and sometimes a max range, the 'hell' of data presentation).
Can somebody tell me if it is possible what I want and point me to a component that can do what I want (in isolated form ofcourse)?