a question for transformer buffs

[glinjik]

i have basically little knowledge of smps transformers but i see on the little smps module i have the ac comes in to i guess a big filter type thing looks bit like a transformer then into a small 4 pin bridge rectifier that goes to a big cap after that through a fuse a diode then to a small transformer my question is if a replicated that bit could i use the outputs of that transformer for something else im thinking of the big computer atx transformers ? and how useful would that transformer be?

[bob91343]

The first 'transformer' isn't a transformer at all.  It's a common mode choke.  From there you go to a rectifier that provides dc that is filtered by an electrolytic capacitor to provide potential to run the unit.  At that point, there is a transistor that is switched into a transformer at a high frequency, and subsequently rectified and filtered.

So the short answer to your question is no.  You need to get deeper into it to understand what's going on.  The engineers didn't go through years of education to do a trivial job and if you want to do what they do you probably ought to hit the books.  There are cosiderations of switching speed, frequency, duty cycle, and more that need to be addressed.

[ArthurDent]

The actual transformer in a SMPS is designed for the specific IC that drives it at the specific frequency and has the specific size and number of turns of wire on the secondary for the specific output. In order to reuse the transformer you would need to know a lot of the design information that went into the original design. As to how useful it would be would depends on your needs.

It would be a lot easier and safer to try to reuse a line frequency transformer and make a linear supply.

[glinjik]

yep your right out of my depth but i am curious of course that's why im here ive a lot of these old atx power supplies lying around so just thought maybe but no going to leave alone..... for now

[CatalinaWOW]

All of the prior answers are correct, but perhaps a little negative.

The transformer and associated circuitry have had a lot of thought to optimize efficiency, cost and to some extent size and you would need a big percentage of the designers training and expertise to duplicate their results.  But if you are willing to accept lower levels of performance these transformers can be used to make home brew switch mode power supplies.  You will still need to learn more than you apparently do now, but far short of a full engineering degree and specific experience with SMPS design.

Don't be afraid to learn a little and try something.

[Jwillis]

yep your right out of my depth but i am curious of course that's why im here ive a lot of these old atx power supplies lying around so just thought maybe but no going to leave alone..... for now

Don't let complexity scare you . For every large complex design, it's made of many smaller simple designs . Understanding how those smaller simple designs work takes the mystery out the bigger design.
If you look at a  SMPS, it simpley takes a high voltage AC voltage  and converts it through a rectifier to make a high voltage DC. It is then "switched" into high frequency osculating voltage into a transformer that converts  to a low voltage oscillation.Then its rectified again into  low voltage DC. This of course is all controlled with a feed back. from the low voltage side to the high voltage side 
The higher the frequency the smaller the transformer can be. This makes for a compact design that can deliver plenty of power.
 But there are always trade offs because no design is perfect. SMPS are very noisy because of the high frequency switching. This noise can propagate back into the mains effecting other circuits connected to that main supply .It can also cause problems with the circuit that uses the SMPS.  So filters need to be incorporated at both ends to reduce the noise EMI (electromagnetic interference ). 

The block diagram below will give you an idea of how to separate each stage of the SMPS into smaller pieces .  Learn how each stage works individually and it will become easy to understand.I included a few notes of some of the components that are used in each stage.

[glinjik]

i am only learning electronics as a hobby and do basic repairs at home I've had a lot of luck with that, I'm not a kid I'm 50 when i was young i was always interested in electrics but never had the chance to go to college etc i left school at 16 got a job money was tight we were in a recession in the UK 6 million unemployed so money for buying even books was not available so after working for a few years getting no where i joined the army spent 17 years there but life moves on hobbies dont really get a chance moving around bring up the kids but i did manage to get a reasonable pension enabling me to retire this year and that's why i now have time for hobbies i live in a forest in Russia so yep parts are hard to obtain and expensive so i use what i have fix what i can yadda yadda i guess some people think there above others you find this on all forums i take little notice of those people i know what I'm capable of, without any training I've built my own house from the ground up installed my own solar and wind gen, put in the systems septic water heating all with no degree, I'm a life long fiddler i can't help it oh i installed the 240 3 phase electric in my house as well not bad for a no nothing guy however i like to ask questions I'm well aware people know a lot more than me maybe some folks should remember this bit of the forum is labelled beginners  I'm happy and yep I'm still going to burn myself on the soldering iron, and trip the mains with my experiments shock myself again but I'm having fun and negative comments..... well i am polite but yer could not give a monkeys uncle  rant over