Hi, I'm working on a design for a new device.
It needs to be powered from an AC ( 100-265VAC ) power source. I need an isolated 5VDC at about 500mA, as well as a non isolated supply at 3.3V at about 150mA
The isolated 5V supply is for running a microprocessor plus some associated driver circuits.
The non isolated ( with respect to the AC ) 3.3V is for powering an IC and opto-isolators, the IC is sampling data from the AC power supply.
I'm considering using a UCC28700 controller to provide the isolated side, I'm debating how to do the 3.3V side and would appreciate any comments.
Options;
(a) use a cpacaitve power supply for the non isolated side. Quite simple but the capacitor gets pretty big and chunky. I'd need something thats 1" x 1" x .75" and those parts are not so cheap.
(b) have a second AC/DC non isolated converter, just for the 3.3V.
(c) Use a DC/DC isolated converter to convert the "isolated" 5V to a 3.3V on the non isolated side. This right now looks like my preferred option.
Any comments?
