Electronic – Grounding a switching PSU with AC mains neutral

mainspower supply

I'm working on a circuit that measures mains current/voltage. I've seen the usual setup where a half wave transformerless simple circuit is used to supply couple of miliamps of power to run the IC that does the measurements and after that, an optional optocoupler is used to communicate with other ICs that run on isolated PSUs.

In my circuit however, the combined power consumption is in dozens of milliamps and the simple PSU above will waste too much power. I thought, why not connect the ground of a regular switch mode PSU ( e.g. a mobile phone charger adapter) to the mains' neutral lead and use it to power up my circuit. I've since been trying to find a problem with this solution and couldn't. Can anyone think of any problems or perhaps other solutions?

Note: I'm aware that such a circuit would be dangerous to humans without a proper enclosure (e.g. in case the live and neutral leads are swapped).

Edit: I didn't know how easy it was to add schematics here, so here's one to show what I mean:


simulate this circuit – Schematic created using CircuitLab

Best Answer

A switcher that runs from the AC can have its isolated output connected to the neutral. Make sure it is an isolating switcher though.