System blocks of switching power supplies

Question

I want to design my own power supply. I know it can be dangerous for someone whit not much of experience, but at least I want to learn it on the paper!

I am aiming for a 12 V/10 A (120 watts) DC switching power supply.

What I think the system block should look like

1- 220 V AC to some DC value this will be mainly a transformer, plus usual filter caps, etc...

2- A switching IC to convent the secondary side of the transformer to 12 V

3- Some safety ideas:

• over current -> monitor output current with a shunt resistor
• over voltage -> ???
• over temperature -> a microcontroller with some SMD temperature sensors around hot areas (switching FET, etc)

The questions are:

• I would need to search for a transformer which is rated for 12 A? 12 A being my output, so maybe the transformer must be rated higher because some energy will get lost?

• Are there any standard schematic (opensource hardware, etc) that I can take as reference?

• Where I can find any reference?

• In general what should be careful about, dos and don'ts?

Answer 1

I am aiming for a 12V/10A (120 Watts) DC switching power supply.

OK

What I think the system block should look like

1- 220V AC to some DC value this will be mainly a transformer, plus usual filter caps, etc...

2- A Switching IC to convert the secondary side of the transformer to 12 V

Here's where you are going wrong. A switching supply or converter powered from the AC mains will: -

1. Rectify the AC directly
2. Smooth the rectified mains to produce a fairly ripple-free DC voltage of several hundred volts
3. Use a switching circuit (including a switching transformer) to convert to a low voltage, high current DC output.

For instance, here is a circuit of a 15 volt, 7.33 amp DC output flyback converter that incorporates what I mentioned above: -

That circuit came from this data sheet by Premier Magnetics and, in turn, that data sheet was found by referring to this general guide on various switching power supplies.

3- Some safety ideas

All the ideas are good but the basic designs you will find won't usually include those features. You have to shoe-horn those features in yourself.

I would need to search for a transformer which is rated for 12A? 12A being my output, so maybe the transformer must be rated higher because some energy will get lost?

You will be searching for a switching transformer and not a regular AC mains transformer so, use the Premier Magnetics link above to get a feel for what they are all about.

Are there any standard schematic (opensource hardware, etc) that I can take as reference?

Premier Magnetics appear to be the most complete that I have come across.

In general what should be careful about, dos and don'ts?

"Off-line" converters might be too big of a hurdle for you at the moment but, going down the route you suggest in your question misses the point about converting AC mains to low voltage DC.

_{I have no affiliation with Premier Magnetics; I just came across their website several years ago and find it a useful reference at times like this.}