I need 220AC to 5V PSU for exhaust fan controller, the trickiest part – it should be as small as possible. The main load is LEDs, same time supplied voltage should be clean enough for analog to digital conversions doing by attiny85. So I bought and test 6 different PSU. Because of seller mistake one of them turned up to be 220 to 12V PSU, so only 5 of them were tested.
All of them produces awful output exception of #1 and #3 (hilink)
The winner is #1, it’s one of the smallest (12X25X18 mm), one of the cheapest ($0.77), rated at 5V 700mA power supply.
No one of them (with exception of hi-link) doesn’t look safe enought to be treated as galvanic isolated PSU.
Here is a table for quick comparison, but out of the box (without changing capacitors or adding filters), only #1 and #3 worth to buy:
On all oscilograms below, red channel in AC input mode, yellow channel DC input mode.
The first PSU utilizes some unknown IC mounted under transformer, I see no optocoupler/tl431 on the board, but I see that transformer has 3 windings, most likely IC uses on of the secondary winding for voltage stabilization. Because of dense mounting, absence of isolation cuts and exposed pads of the hot side, it should be treated as a power source without galvanic isolation. PCB marked as WX-DC1203.
Here is oscilograms with different loads:
The second PSU looks similar to the first one and most likely shares similar topology, but it has one of the noisiest output, PCB marked as RPD5W5L:
The third is Hi-Link HLK-2M05, it has the best output. Same time it’s the biggest, the most expensive and have the lowest specified power rating, only 400mA. Schematic topology is unknown, because of the case filled with silicone, but Y capacitor is a good sign:
The forth PSU share similar topology with the first two, used IC has marking FT383NB:
Here is a typical schematic for that chip, as I expected it uses auxiliary winding for voltage regulation, here is a schematic from datasheet:
PSU has the worst, the noisiest output:
The last one has the most complex schematic. It utilizes IC THX208 and has pads for additional linear regulator. I had great hope about it, but it turned out that output is fairy noisy, PCB has marking SM-PLA038:
Here is typical schematic from datasheet:
In conclusion: from my point of view the first one is the best by the ratio price/quality until you have guaranty that no one touch cold side.