[SOLVED] Urgent help is needed for SMPS project.

Finally got it working. With first transformer bad ringing rewound in second sequence (as mentioned in post#18).Unregulated output 18v,2.75A without significant voltage drop.
Regulated it to 12v with a resistor and zener diode at 4N35 optocoupler.Don't have an oscilloscope at the time to run the tests,May have one soon and build some advanced circuit of SMPS After completion of the reading of book for SMPS design which i am studying already.
With help you guys i got things made easy for me to understand better.Love it.
Thanks a million,friends.

how u find the core number,is it printed on core like EI-33, E-42

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NO. As i salvage them from computer psu,TV,VCR,Monitors,printers and any other dead equipment with Smps based power supply inside.
I never found a core with part number printed on the core itself.AS they are always salvaged and being never able to find a new one in our country,it becomes a tricky (actually way too tricky)business to work with these cores.
Some time the manufacturer of the ferrite transformer puts a certain code on the tape wrapped around the core which may have initials for the core geometry and physical size.Some time they just mix it with the code even some time no such initials are given and the part number is customary to the manufacture.

Getting the physical dimension of the core it easy,you can use just a ruler and measure the dimensions(it is to be measured for one half of the core).
Then you have to open the core.There are more than one way to open it.They are prone to break with small force and broken core is useless no matter how you can fix it it will never work properly or may not work at all.
After opening the the core you have to see the center leg if it is square or round or spherical in shape then you need to measure it and count the cross sectional area.There is a separate formula to count for each shape of center leg and it is an important part of design.
When you are done with measurements you can search the net for equivalent part data sheet.But this data sheet may not be of any use other than you can just confirm the dimensions you measured and part number.
The core material is most important factor and is different from one manufacturer to the other and there is no way to measure it until it is known to you already.
Further,for same dimensions there may be different types.

i hve only experience in EI core 50 Hz

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EL 50hz is steel sheet strips core for 50-60hz mains AC operated transformer.
Ferrite cores or not for mains AC operated core. There general way of working is same as for 50hz cores(conversion) but they are entirely different. These are DC operated high frequency cores (most of the times) designed to work from few Khz to several hundred Khz.
You can't just put them to DC source they need to be operated with driver circuitry either single transistor or dedicated chips.Most common way is pulse width modulation and many more.

I myself am still learning and has a long way to go yet for perfection.

Thank u liteon for the explanation in detail.plz stay touch to find out further,bye the way where u live in Pakistan.lot of appreciations if u answer. Previously u helped me lot for finding thermal grease.thanks

bye the way where u live in Pakistan

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I live in a remote area of district BAHAWALPUR, south PUNJAB right at the start edge of desert Cholistan.And my house is more close to india than LAHORE.And its been more than 6-months since my last visit to Lahore.I travel as low as possible, i am not comfortable with traveling.And the city of HASILPUR where i live has much advanced in recent years and we got every necessity of life here,even Broadband and wireless 3G.
But yet the city is low on electronics parts stores.I always found the parts which are expected to be available here and not the most of i needed.So some time i have to travel to other cities but no just for parts but when i have to visit a city for my job work i buy the parts from there if available and most of the time Multan comes first and Lahore second and then Rawalpindi.
One thing you must know that i am not a professional in field of electronics.It is just my hobby.My profession is entirely different.

Thank you very much Choudhary Wazir. I am impressed , you have such a good heart.My name is Choudhary yasir arafat.
You live in a big place thats such a big advantage.Big things happen in big places you know.Good to know that you are professional and indulged in inverters and medical instruments.I think medical instruments their repair or servicing is a job to be taken quite seriously,as their usage belongs to human life so needs highest level of experience.
About my further details, i hope you not to mind please,but i think it is not good to put your personal information on the net until and unless there is no other way.And the cell number is way to serious.
Yet i will tell you that my profession is nothing fancy but very respectable,I am not a public servant controlled by the rules of government,Me and other professionals of the same line are controlled by the rules of and by autonomous body itself all over the country yet the profession is related to the service of public.
Any way,i got your cell number saved.May call you some time and you will get my cell number.Till then please see my e-mail id in my profile and you can send me an e-mail if you want, whenever you want.I shall always be much happy to share the knowledge with you.
Much obliged.

dear liteon,
thanks so much for sincere advice,love to care further.

You may edit your post and remove you number.

respected Liteon,
many many thanks,you are really serving the people a lot,please send me some formulas
for winding of SMPS Core if available,
Thanks&Regards

brother ch wazir. There are different topologies to make a SMPS.As i said in my earlier posts that i am studying a book about those topologies ,and yes there is a lot of math and formulas involved.I am sorry for being not able to help you at this time but may soon be able to share with you what i learned.
The web is full of smps projects based on all topologies but as you know we got a limited window to implement those ideas in our desgins for one reason and one reason only, The "new ferrite cores are not available in our country" and to make a safe and efficient Smps we need to know a lot of parameters about the core.But when cores are salvaged from dead equipment there is no way know all of those parameters so any attempt may fail for this reason or their will be bad efficiency.In both cases it will not be appreciable project.