Choice of switching regulator IC

[autir]

Hello all 

I have decided that the new project I want to build ( a 1.2-30V, 3Amp variable PSU) should have a switching regulator IC instead of a linear one.

After a search I have decided that National's LM2576T-ADJ is an IC well-suited for my needs.

Does anyone have to propose a different solution? It must be in a package suitable for stripboard (TO-220 etc.), and a decent price (<5 Euros) would be a plus.

Thank you.

 

[walid1]

i think this is not the problem.....
A switched mode power supply (SMP) uses a ferrite core transformer, how you will get it .
If I in place of you i get this psu from a used computer monitor and modified it , or simply analyze it and understand the design.

 

[autir]

If you take a look at the datasheet, the adjustable output voltage version is what I have in mind. There is no ferrite core transformer in this circuit (or in any other circuits in this datasheet, if I'm not mistaken).

Another problem:
How could I provide the unregulated DC input voltage without use of any heavy power transformer?

 

[ante1]

Hi autir,

You could go for a primary switched PSU, no heavy transformer, small size, high efficiency, very small heatsink and heat loss!
What more could you ask for? ;D

 

[Alun]

Good idea Ante, but just make sure you add good enough protective devices like fuses and thermal cutouts safety 's sake, also ensure the transformer's primary and secondars are isolated by a good thick layer of insulation tape. Personally I wouldn't recommend building a mains primary switched PSU as it's not always easy to make it safe, under these circumstances I'd recommend an off the shelf solution.

 

[ante1]

Hi Alun,

The IC:s which are made for this purpose are equipped with several options for various kinds of protection. The standard way of doing this is by means of a galvanic insulated transformer…. as every transformer actually is made!

 

[autir]

You could go for a primary switched PSU, no heavy transformer, small size, high efficiency, very small heatsink and heat loss!

Yes, that's what I want 

Have you got any tutorials/ docs in mind? What should I read to know how to start?

 

[ante1]

Hi autir,

I don’t have anything ready for you but take a look at : http://www.semiconductors.philips.com/acrobat_download/datasheets/TEA1552_2.pdf
It might give you something to start with.
Similar ICs can be found with other manufacturers too.

 

[Shahriar]

The main problem in SMPS Designing is the transformer calculations.
The best thing you can do, is copying from a TV schematic and buy the transformer. because finding the TV transformers is not very difficult. and the schematic is on the WEB  ;D

HTH - Shahriar

 

[ante1]

It’s also possible to modify an old PC PSU to make it variable and change the voltage to any voltage you need.

 

[harrychoo]

I also having difficulty to understand the high freq transformer. I dunno how to read their specs and which spec i should use. Any help pls? Thanks

What core of the transformer and what switching frequency normally being used?

 

[ante1]

Hi Harry,

This might be useful: http://www.electronics-lab.com/forum/index.php?topic=4523.0