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Flyback converter (110-220v line power to 5v)

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benjius:
Hi,
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):



But they seem unsafe and I don't like them, I'm looking for something more robust.
I found the fly-back converter with secondary current and voltage regulation implementation, commonly found on wall adapters for cellphones.



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.

PF0037 From Pulse
CVP11 Series from Cramer Coil

Future reading I found that I could buy a EE16 core and wind the transformer myself but I know nothing about that either.

EE16 Cores

I've some questions that google can't answer.

Can you manually wind a tiny flyback transformer ?

If someone has experience with these designs I would greatly appreciate any advice.

Thanks.
Ben.

Psi:
You would need 7uF of mains rated capacitors to get 500mA in that first circuit anyway, those kind of power supplys are only physically small if you need under 100mA.

tyblu:
Have you made a SMPS before? This is quite the variation on one. I don't get it on first inspection. Are you able to analyze it? If not, stay clear, as you'll just get zapped and die.

benjius:

--- Quote from: tyblu on December 12, 2010, 12:32:57 am ---Have you made a SMPS before? This is quite the variation on one. I don't get it on first inspection. Are you able to analyze it? If not, stay clear, as you'll just get zapped and die.

--- End quote ---

Yes I've done a few DC-DC StepUp SMPS in the past but based on 555 timer chip (for my nixie clock)

As for playing with high deadly voltages:
18 Years ago when I was maybe 11 or 12 years old I promised mom and dad that I would not be killed an electrical shock and that I would stop playing with mains electricity for ever, (They found my playing with an old motor I picked up from the garbage)

Since then I like to keep my projects running on low voltage, my nixie clock is the only high voltage project I've done.

My last project was the first time I worked with 220V/AC and to be honest I was fascinated by the amount of power you can control with it, it feels really powerful and I learned a lot !

The truth is that I've no other option for my project and this feels like the one I've to go all the way !

You can buy assembled modules that would do just that 220v -> 12v 150mA but I can trust those vendors, also they add significant cost to my design.

I'm really thinking about winding the transformer myself, but I don't want to fall into a deadly trap !

Thanks.
Ben.

mikeselectricstuff:
Power Integrations also do loads of simple SMPS controllers for small mains PSUs like this, and I think they have teamed up with a magnetics supplier to provide standard transformers.
But why reinvent the wheel? - there are  a gazillion ready-made PSUs available off the shelf at prices not much more than you could make them for, and someone else has already done the safety engineering and got all the approvals work done.
Unless you have a particularly unusual space constraint which can't be met with an off-the-shelf unit, or are into very high volumes I don't think you will save any money by rolling your own, even from a standard chipset.

Incidentally if you need a non-isolated supply for more than practically can be done with a capacitive dropper, Power Integrations have some really nice cheap chips to implement mains-input buck regulators - Linkswitch TN series

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