I've been trying to come up with a really small design that will take mains line voltage in the range of 90-250 volt a/c - 50/60 Hz and output
5 / 3.3volt at < 500mA.
I don't want to use a big transformer+linear regulator because of the size !
I've seen implementations like Microchip AN954, (capacitive and resistive PSU):
Then I located the ViPer family of devices from ST, specifically the VIPER12A which can handle a bulk and flyback configurations.
It provides some sort of protection and I like them, they come in DIP package and most important I can source them in my town !
From the app note "AN1484":
The circuit is a standard Flyback converter with secondary current and voltage regulation driving the VIPer12A feedback pin through an optocoupler.
This is the design I was looking for !, it's small, safe and it's been used all over the world but I know nothing about them :o,
I feel I'm going through the rabbit hole and things get complicated every step of the way.
First and most important it's very hard to find the correct flyback transformer, the two vendors I found don't have a sales webpage they work only
through distributors, and even then I'm not sure about the stock.
Another app note AN2097 from ST has some more information about the transformer. AN2097 is for 12V output, so you have to reduce the secondary winding from 17 to 7 for 5V output, two or three parallel 0.6mm wire for higher current output. PC48EI19-Z (TDK code) EI type ferrite core may work for this type of load. Since there are so many different types of SMPS transformers that there may not be ready made commercial transformers for this applications.
ReplyDeleteWurth Electronik make some flyback transformers for use specifically with Viper and other SMPSU ICs. Alternatively you could try slavaging the transformer from a cheap plug-in-the-wall mains adapter/ charger which use the same IC. Or you could wind your own - if you have enough knowledge!
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