This is from ATM90E26 Application note, this IC needs to be connected to mains in order to measure voltage (220VAC) and current. I tried to look for information about the transformer "TD35-18A-220V"(turns ratio, inductance, etc) but with no luck, all I found was a link to buy bulks of 1000 pieces and no specifications.
So I started to look for a similar one and found this one from wurth elektronik: 750342104
According to datasheet for 78L33 maximum input voltage is 18V, so the position of terminal 2 of the transformer (I mean the ratio of (1-2):(2-4)) should be specific to get that output level from terminals 2 and 4, as in the circuit on the first image (terminals 3-1).
From isolated side (terminals 6-10) should be power for digital control electronics, microcontroller and the rest of the circuit (250mA top current). And an isolator (SI8651BB-B-IS1R )to connect the microcontroller to the non-isolated from mains ATM90E26 IC.
My question is if I'm looking at this the correct way?
Is the turns ratio for (1-2):(2-4) a percentage style ratio?, meaning if 220V is the voltage between 1-4, then, if I looking to obtain 15v between 2-4, terminal 2 will be at the 6.81% of the turns between 1-4?
Does this means that the transformer needs to be specific and not "off the shelf"?