3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applications

Thread Starter


Joined Jan 2, 2012
I am currently working on a 3 phase energy meter project. I don't have a lot of experience in designing power supply circuits (AC/DC) let alone a 3 phase 4 wire one (L1,L2,L3 and N) with a transformer to be galvanically isolated. Since energy measurement is being done for all three phases, the metrology (Microcontroller + metering IC) part must be able to measure energy even if two phases go out, so AC supply must come from all three phases. I've scoured the internet and found a few approaches, some used a transformer, some didn't.

1. My findings

  • A fellow user here asked the same question but had a cumbersome solution(3 transformers) and didnt want an isolated supply.

  • TI and AD have a few application notes for whole energy meters but their power supplies are transformer-less (bummer).

  • ST has a lineup called VIPER (rectification then flyback DC/DC) which has a transformer based schematic but for prototyping i think the design will take some time to perfect and i'm looking for a faster temporary solution to focus on the computing part of the system for now.
2. My questions

  • Can i use something like this ( IRM-20-12 ) for the time being or if there is a better model please let me know. If the answer is yes then i think the next question is how do i connect it to all 3 phases since the power module only take Line and Neutral ?

  • If the answer for the previous question is no, what would be my options for a prototyping stage and another for a cost efficient and not so brutal to design ?


Joined Dec 2, 2013
A power energy meter is a complex thing hence experiences needed.
It should be able to handle phase shifts caused by loads, unbalanced, between two faces only and floating zero.

Power meters full calibrated and certifiet are on the market for a 200-500 dollar/ Euro.

The time to design, build, test,calibrate and certify goes in the thousands.

Why destroy money?