220vAC to 3.3vDC conversion in small area

[Karamel]

Hi,

I have to convert 220v AC to 3.3v DC in small area like phone charger case. I need also less than 50mA so, I thought, I can implement any phone charger circuit in my design but, unfortunately, I have no any idea about them. Can you suggest anything about this problem solution method and any circuit diagram?

[JacquesBBB]

You can get one of these  AC-DC module  for 5.99$
https://www.mouser.fr/ProductDetail/MEAN-WELL/IRM-01-33/?qs=C9r8PV%2f%252boWPYMhpLuTFr9w%3d%3d

Or if  you are more adventurous, get the  ebay 2.57$ one
https://www.ebay.com/itm/HLK-PM03-AC-DC-220V-to-3-3V-Step-Down-Buck-Isolated-Power-Supply-Module/311759562967?hash=item48965168d7:g:7cYAAOSwzSRZy3EI

[The Doktor]

I've tested a few examples of that ebay "Hi-Link" supply, both 3.3V & 5V using my DC load. Input was 125V 60hz. Output was clean & on spec. They weren't too warm after an hour at full rated load, and it takes around 50% overload before they go into protection mode. Will they last? don't know. But they do work as advertised.

[amyk]

Do you need isolation? If not, this is within the current range of a capacitive dropper.

[mariush]

If you don't have to make it the cheapest, you could go with a classic transformer , a bridge rectifier and a switching regulator after that.

Here's an example: https://www.tme.eu/en/details/bv2020154/pcb-transformers/hahn/bv-202-0154/

It's only 1.5$ in volume (2$ if you buy just one),  around 35g , 23mm by 22mm and 15mm tall and can be soldered directly to the pcb (has pins going down) , outputs 6v AC at around 83mA , which means after rectification with the bridge rectifier you'd have around 7v DC and 50mA.
From here, you could either use a simple LDO or linear regulator to get 3.3v and 50mA, or you could use a cheap and simple switching regulator will easily convert this down to 3.3v at up to around 90mA  (assuming around 90% conversion efficiency).

Saves you the hassle of making the high frequency transformer, with double insulated wires, all that insulation between windings and so on...

If you want something super flat and again money is not an issue and you can live with only a max of around 30mA, you could go the no transformer route.

Use a diode and a capacitor to do half-wave rectification and feed the linear regulator with at least output voltage + 12v      
LR8K4-G  takes up to 440v DC and outputs 1.2v .. [input voltage-12v] at up to 20mA. Configure it to output something like 40v..60v at 1-2 mA , then use a switching regulator to convert 40..60v to 5v at 100mA
Then use a digital isolator like Adum5010 to isolate 5v and get 3.3v at up to 33mA (100mW) with an efficiency of around 30% (that's why you need 5v @ 100mA

No transformers, super flat, but the linear regulator will dissipate around 1-1.5w of heat constantly while the adapter is plugged in, and you're losing another half of watt in the conversions... so your adapter will be extremely inefficient.

[grifftech]

phone charger plus to-220 version of this: http://www.ti.com/lit/ds/symlink/lm3940.pdf