step down switching power supply design

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kuldeep

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I want to design a step down switching power supply ckt with following specs:

I/P mains:
240V(~), 50Hz.

O/P:
15-20V, 2-3A

I'm new to power supply design, so please provide me information related to standard techniques, circuits and components.
 

If you dont have any experience with HV HF transformers you better start with a step-down transformer 240Vac/24Vac, use bridge rectifier and a ≈4700µ smoothing capacitor and then employ one of the switchmode step-down (buck) converters such as LM2576 or similar ( **broken link removed** ).

Once you gain experience in switchmode regulators you can switch to direct conversion from 300Vdc (240V after rectifying and smoothing capacitor will give you ≈300Vdc unregulated voltage) to 24/30Vdc.
Here is some info on the above:
http://www.onsemi.com/pub/Collateral/SMPSRM-D.PDF
and on SMPS transformer calculation
http://www.fairchildsemi.com/an/AN/AN-4102.pdf
 

Right now I'm using a step-down transformer (240Vac/12Vac) and LM2576T-3.3. The inductor (100uH, 3A) specified in datasheet is costly. Can I go for a approximate value inductor? The transformer cost makes the power supply even more costly.

I'm looking for a cheeper solution.

Thankyou, I'll go through the documents.
 

With little change on the output transformer, the following circuit may fit your need.

hXXp://focus.ti.com/lit/ml/slup058/slup058.pdf
 

I suggest the following.

Visit www.powerint.com
Download PI Expert this will help you a lot in designing a SMPS like you wish, inclusive you will get detailes info in how to build the power inductor ( transformer )
Dont miss their application notes and tutorials.

Another site ( consider that most os power semis manufacturers give a lot of info ) is www.onsemi.com they bring a limited version of POWER 1-2-3 wich will allow to simulate your circuir ( of course using ON Semiconductor parts ) but anyway will be useful if you realize how ( askme if U don´t realize )

TI, FAIRCHILD, ST, PHILIPS, INFINEON, IR are also places where U willl be able to find lot of info and design guides.

Hope this help U
 

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