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I'm designing a project that controls 110VAC (plug in, socket out), and also has a microprocessor inside. I'd really like this project to not need a wall wart to get it's 5V, so I want to include a small DC power supply inside.

Apple's USB power adapter looks like a great small design that I can fit inside my case. I'm guessing this is a switching power supply but I can't find any teardowns or schematics anywhere.

Does anyone know how this thing works? I know I could make my own 110V->5VDC supply from a bridge rectifier and some caps, but I'd like to also be super safe. What's in the Apple brick?

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  • \$\begingroup\$ something like waldok.com ? \$\endgroup\$ – kenny Apr 4 '11 at 22:27
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    \$\begingroup\$ Take one apart and find out what's inside \$\endgroup\$ – endolith Apr 5 '11 at 15:34
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    \$\begingroup\$ endolith: I did and found Chinese HV BJTs almost nobody heard about, a transformer, several resistors and residual flux all over the place. ;] \$\endgroup\$ – jpc Apr 5 '11 at 22:29
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You're in luck: I just posted a detailed teardown and schematic of the iPhone charger. Internally it's a complex flyback quasi-resonant switching power supply controlled by a L6565.

Building your own switching power supply is probably more complexity and danger than you want to include in a project. I'd recommend going with the wall wart - there's a reason most products use one. If you really want a built-in power supply, I'd recommend getting a pre-built OEM one rather than building your own. And if you really want to build your own, I'd recommend a simple linear power supply instead of a switcher.

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The simplest way would be probably to buy a USB power adapter (probably not from Apple but a cheap replacement) and use this (preferably without removing it from the casing to avoid any electric shock hazards).

If you are not experienced with electronics I would suggest against making you own power line switched-mode power supply.

You could also easily do a small transformer based supply but it will be quite a lot heavier and larger than the USB "chargers".

For mass-market solutions you may check LinkSwitch chips. They are quite cheap and require almost no external components. I am afraid that in small runs you will have a problem with obtaining cheap ferrite power transformers but I would love to be proved wrong on this one.

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  • \$\begingroup\$ Thanks for the concern. I don't need to reinvent the wheel, I just need to locate the components and/or schematic to implement this small power supply in my design. I plan to build a small run of these devices and I really don't want to tell my CM house to "buy these dongles from monoprice and tear them apart". \$\endgroup\$ – zydeco100 Apr 5 '11 at 16:14
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    \$\begingroup\$ Sorry, your intent for manufacturing was not apparent from your question. Maybe check the LinkSwitches I added to the answer. \$\endgroup\$ – jpc Apr 5 '11 at 16:35
  • \$\begingroup\$ Those look a lot easier to get and come with reference designs. Thank you. \$\endgroup\$ – zydeco100 Apr 5 '11 at 20:28
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Here are some photos of the Apple iPhone AC adapter, it's got two small boards with components on both sides of each. For the power output it could not be anything other than a high-frequency switching regulator. However, the controller IC is not marked with a part number. I tried to track down who made it, even contacted an EE Times editor to request a teardown article. He asked Portelligent for their teardown but they had to look at the bare IC under a microscope to find the ST logo and even then they weren't able to point to a publicly available part. So either it's something custom for Apple, or Apple got temporary exclusivity before the chip was released generally. A few clones of the adapter have appeared on the market so there must be something available by now. http://www.myinnergie.com/mMiniAC/

For your purposes, assuming you don't need several watts to run a little microprocessor, there might be a solution that's much cheaper or less complex.

iPhone AC adapter, view 1

iPhone AC adapter, view 2

iPhone AC adapter, view 3

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  • \$\begingroup\$ Samxon in an Apple product? Pfft... \$\endgroup\$ – Thomas O May 19 '12 at 19:08
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Looks like MAX 611 couldn't make it any easier: http://www.selectronic.fr/includes_selectronic/pdf/Maxim/MAX_611.pdf (sorry about the random site, not turning up a link on Maxim's site).

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  • \$\begingroup\$ Wow, thanks for finding that. That looks like a perfect part...if only it was easy to find. I guess that's the next challenge. And that leads to another question: why haven't more people used this part before? The MAX611 datasheet is from 1994. The difficulty seems to be trying to get an isolation transformer that's small enough. \$\endgroup\$ – zydeco100 Apr 5 '11 at 2:19
  • \$\begingroup\$ Interesting part, but the datasheet's dated 1994! \$\endgroup\$ – blalor Apr 5 '11 at 2:21
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    \$\begingroup\$ These chips are mostly for non-isolated supplies which are not something you should be using for hobby projects. \$\endgroup\$ – jpc Apr 5 '11 at 11:05
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    \$\begingroup\$ @zydeco100 They use switch-mode supplies with small ferrite transformers for designed high frequency of operation. The problem with these is obtaining the transformers (they are either expensive or custom designed and made in large quantities) and making the SMPS robust to surges and stuff (traditional 50/60Hz transformers give this one for free). \$\endgroup\$ – jpc Apr 5 '11 at 16:38
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    \$\begingroup\$ zydec0100: Of course it's not easy to find! It's a Maxim part! They make lots of neat parts you will never be able to source in quantity at manufacturing time because they've driven away all of their distributors. \$\endgroup\$ – Ben Jackson Apr 5 '11 at 16:59
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The safety first. But you are describing some rare case, when galvanic insulation is not needed that bad. To provide the power with 3-5 volt and low current you can use UL certified capacitor under 1 uF, diode bridge and zener. but only and only if total current is less than 10-15 mA. With larger current things become difficult because of thermal dissipation and real fire hazard dangers.

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