Help me build a SMPS for a laptop (16 V 4A output)

laptop power supply boost converter

I have built a linear regulated power supply, and have found an abundance of information on how to go about it.
Now I would like to build an SMPS that can be small enough to be portable (for a laptop).

Although the building of a linear power supply is - relatively - straightforward and there is an abundance of information on the net, I could not find any information on creating an SMPS suitable for a laptop.

The required output is 16V 4A.

What I have managed to understand so far:
1. The 230VAC input is switched to a much higher frequency (a few 100's Khz)
2. At those frequencies the stepdown transformer can be MUCH smaller due to higher impedance.
3. A buck converter is sometimes used at the output.

- What sources of information are available for this kind of project?
- Although I've tried my best, I could not find a guide to selecting a transformer for such power supplies (type, ratings, etc...).
- Is the switching applied to the raw AC or is it "flattened" out first?
- Does a buck converter require a ferrite core? (I've seen schematics that use air core and others that use ferrite)

Thanks for any help.

djinng

According to me the laptop power supply should have the following features:

1. Universal input: 80VAC to 270VAC
2. Power factor correction
3. No mains transformer to step down the voltage.
4. PWM for o/p voltage regulation
5. HF transformer for isolation.

This may seem a lot but take a look at: UCC28512 from Texas instruments and you will have your problems solved. TI even has a few eval boards for $50.

Tell me if you have other things in mind.

bimbla.

Re: Laptop power supply

Thanks alot bimbla!
It really looks like what I've been searching for.

Browsing through the spec of the IC, I got the answer to most of my questions:
- first, AC is rectified, then fed into a boost converter where it is switched at ~200 Khz, and then fed into a flyback or forward converter.

Now the only thing that seems as yet beyond my reach is the knowledge that will allow me to calculate and select the proper components for this project.
I'll keep looking at TI's site for boost & flyback design documents. Any good ones you know of that focus on component selection?

Re: Laptop power supply

**broken link removed**
**broken link removed**

This is the link for the UCC28517 datasheet. A reference design is included in the data sheet. Explanation for the same along with procedure to design (calculations) individual components. I feel it is sufficient. I suggest that you verify the reference design values before you try to calculate values for a new design.

The second pdf details the evaluation board available for the same. This should give you the confidence to build your own design.

We can discuss your design as you go along.

Regards,

bimbla.

Re: Laptop power supply

I would not start with a PFC design, especially that you have no experience with switching power supplies.
For this application I would just build a forward converter, using a PWM controller, such as the good old UC384x. The power is relatively low, so it does not justify a PFC and so you need fewer components.