Has anyone seen a schematic and BOM for one of those miniature AC adapters like the Kindle or Apple iPhone uses? I need 5v at about 250mA and I know those little things use USB cables for powering the device, so I know they would work for me, but how do they cram the AC-DC converter in such a small space?

Thanks

 

No offense intended, but if you have to ask, you probably can't build one. And absolutely not for the price you can buy 5V wall-plug chargers at second hand stores. Like $US 0.39 to $US 1.99. Or, ask your friends if they have ones laying around from old phones. I use them all the time for micro-controller projects.

Ken

 

I bought some 5V-2A name-brand power supplies made for telephone modems. They use a modern high frequency switching circuit with a tiny ferrite transformer and the output voltage is regulated. They were surplus so I paid $1.75 for each of them. They are tiny.
A chart on them shows that there is a trimpot inside to adjust the output voltage anywhere up to 30VDC at 10W.

 

I believe the Apple adapters use Power Integration controllers, which have the SMPS controller and power MOSFET on the same chip. To satisfy your curiosity, have a look a their Tiny Switch product family, and particularly at their TNY375PN.
http://www.powerint.com/ and type "TNY375PN" into the search box.

Making these off-line switchers requires specialized equipment to allow you to bring up your circuit safely, and some specialized training. For example, you might have to wind your own high frequency power transformers; not a task for the faint-hearted. Similarly, there are electromagnetic interference, thermal, and safety issues need to be addressed.

My advice (even though not requested) parallels KMoffett's closely; unless you are a power supply engineer with a few off-line supply projects under your belt, don't try it. You could end up dead or worse.

 

There are times that I also need a 5VDC power supply inside a device the already has 120VAC. Instead of sticking the whole SMPS wall wart inside the device, I just remove the wall wart's plastic housing. I then mount just the SMPS's PCB inside my device.
http://www.electro-tech-online.com/general-electronics-chat/93884-not-transformerless-power-supply.html#post749571

Ken