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Topic Title: Flyback transformer
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Created On: 20 October 2010 10:21 AM
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 20 October 2010 10:21 AM
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zhassan11

Posts: 10
Joined: 23 February 2010

Is there any difference between flyback transformer and normal ferrite transformer. Also is the fly back transformer designed to be driven by one MOSFET only, so we cant drive it by half or full bridge.

I look forward to some responses!

Thanks in advance.
 20 October 2010 01:52 PM
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ANFierman

Posts: 136
Joined: 25 July 2008

Hello again,

The question "difference between flyback transformer and normal ferrite transformer." is two questions.

i) what is a flyback transformer used for?
ii) what core material is used in the transformer?

Flyback transformers can be used to generate the EHT in CRT monitors & TV's. Here the name derives from driving the transformer at the horizontal scan frequency and using the flyback time to generate the EHT output pulse.

They are also used in the so-called Flyback converter which is a switched mode PSU topology.

Most modern flyback transformers use ferrite materials because they are running at 50 kHz and often much higher than that.

Basic background:

http://en.wikipedia.org/wiki/Flyback_transformer (links to TI notes mentioned later)
http://en.wikipedia.org/wiki/Flyback_converter


which also links to:

http://ecee.colorado.edu/~ecen...als/flyback.pdf


You might find the stuff in here useful:

http://nptel.iitm.ac.in/course...%20Electronics/


which links through:

http://nptel.iitm.ac.in/course.../left_home.html


to

http://nptel.iitm.ac.in/course...lectronics/PDF/


in particular this may help:

http://nptel.iitm.ac.in/course...((EE)NPTEL).pdf


Beyond that, have a look at the extensive apps notes (starting with AN19) from Linear Technology and also this range of well hidden stuff from TI from:

http://focus.ti.com/lit/ml/slup101/slup101.pdf

through to:
http://focus.ti.com/lit/ml/slup129/slup129.pdf


looking at

http://focus.ti.com/lit/ml/slup127/slup127.pdf


in particular.



-------------------------
Andy Fierman

---------------------------
http://signality.co.uk
---------------------------
 20 October 2010 03:48 PM
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zhassan11

Posts: 10
Joined: 23 February 2010

Hello again

Thank you for the reply,

Sorry I thought fly back transformer and fly back converter are the same, may be a different names but they can be driven by single MOSFET are they?

Yes I know about the CRT transformer, in that case my question was about the fly back converter then,

My question is: If I open a product has a MOSFET drive a transformer at 50KHz, can I use that transformer in a full bridge circuit, like drive the transformer with full bridge instead of one MOSFET?

Btw most of the links you sent me are not working;

Thanks again and looking forward for your reply
 20 October 2010 08:16 PM
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ANFierman

Posts: 136
Joined: 25 July 2008

Sorry about the links. I hadn't realised that they'd get mucked up.

If you right click on each, then select "copy link" or whatever it is in Windows, then you can paste it into notepad or directly into a browser but then delete all the spurious characters after the letters "pdf" at the right hand end of the URL.

The IET machinery seems to shorten the URL if it's over a certain length and replace the middle bit with a displayed series of dots. The actual URL is still there but has a sequence of extra characters starting with a % added to the end of the original URL.

Stripping off these extra characters should take you to the sites.

Back to your question.

To answer it you need to understand more about how a flyback converter works. You also need to understand what your requirement is for a transformer in your application. You cannot expect to pick up any old transformer from one that has been designed for one piece of kit or one specific application and expect it to work in a completely different one.

The links I sent you should give you some idea of where to start in your undertsanding. Inductor and especially transformer design is one of the most complicated (and possibly least understood by the most) areas of electronics.

-------------------------
Andy Fierman

---------------------------
http://signality.co.uk
---------------------------
 20 October 2010 11:20 PM
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zhassan11

Posts: 10
Joined: 23 February 2010

Thank you for your reply;

I tried to understand the transformer design but i got confused,

I just tried your links again and they are working now when i copied and pasted into the browser, I will read them carefully to help me understand.

Thanks for your help. very much appreciated
 21 October 2010 03:27 PM
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ANFierman

Posts: 136
Joined: 25 July 2008

"I tried to understand the transformer design but i got confused"

Welcome to one of the darker corners of my world ....


More info:

smps.us/Unitrode2.html
smps.us/Unitrode1.html

Enjoy?

-------------------------
Andy Fierman

---------------------------
http://signality.co.uk
---------------------------
 21 October 2010 09:46 PM
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zhassan11

Posts: 10
Joined: 23 February 2010

lol a matter of fact it is a dark corner

I have a small background in switch mode power supply and ferrite transformers, I knew the design of the transformer is complicated but i did not know it would be as complicated as this.

I did not know the difference between flyback transformer, flyback converter & power transformer. i thought they were all the same.

I have never heard of ZVT power converter

Believe it or not i am enjoying the reading
 22 October 2010 09:06 AM
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ANFierman

Posts: 136
Joined: 25 July 2008

As you have LTspice, have a look through some of the examples and the supplied test jigs for their many SMPS chips.

Also download this:
http://ltspice.linear.com/soft...piceWorldTour2009.zip

and look through the .asc files in it.

You should be able to click on the square button arrowed links in the .ppt file in the zip but they don't work for me.

I don't know how Mike Engelhardt set his presentation and PC up to run them but if you right-click on them, select "Hyperlink" and then search for the "xxxxx.asc" file part under the "Run program" button in the folder, you can start each linked example in LTspice.

Clunky but it works.

You might also be interested to know that TI seem to have made their TINA-TI spice program available in unlimited form. They may have some more SMPS examples.

National WebBench is very slow and very limited in what you can do but some of the other Web tools such as PowerLab that Exar offer are OK (it based on SIMPLIS a very fast switching simulator available from the same people as SIMetrix).

-------------------------
Andy Fierman

---------------------------
http://signality.co.uk
---------------------------
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