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USB Charger Help? Answered

I'm stumped. I built a usb charger with a usb plug in and a battery holder that holds 3 triple a's. I think the output is about 5.10 volts and it charges my flip phone but will not charge my iPhone 4s? Please Help. BTW I am extremely new at electronics. Thanks.


Iphones are tricky. You have to bias the data lines with resistors IIRC. Take a look at the schematics for the "Mintyboost" charger.


I recall seeing some resistor dividers along the D+ and D- pins. This charger may not have those resistors installed.

Once you do get this to work, I recommend buying 2 panasonic 18650 3100mAH Lithium Ion batteries and a charger for them.After fully charging them, go ahead and connect them in parallel to get 6200mAH, and from then on treat it as a single battery. You may consider using a 18650 battery holder to connect them. Make sure it is paralell and not series. Series might fry the phone and/or the charger.


Apple products require a pair of resistors on the Data lines. Why? My only guess is so you have to buy specialty adapters. They change the pinout of their Headsets too (Just one more reason I don't buy apple)

And Totally +1 the 18650, Heres a board that charges the Li-po and also Boosts it to 5V. Sold out Atm but there a many clones out there

It is a development issue with the USB standard.
At the times when high power charging was not defined Apple and others went ways to make a device charge differently from a wall adapter.
The simple approch is what is now standard: Data lines open and not connected means a device draws a max of 100mA.
Data lines shortened and the current goes to 500mA, this is also used if a data signal is present, like on a normal USB port on your PC.
A voltage of around 1.6V signals a wall charger with a limit of 2.1A although most devices limit themself to around 1.6A to have a better lifetime for the battery.
Apple however decided before these things were defined as a standard that it is necessary to have at least 3 different charging modes apart from open (which is no longer supported on never Apple devices) and a data connection.
The car charger for older phones supplied 1.6A max.
The wall charger was available in two variations, 1.6A and 2.1A for "fast charge".
The tablets were supposed to be able to run both on charger and batteries so another variation for the wall charger was "invented" to provide full charging current plus the juice to run the tablet.
All this was solved by different voltages on the D+ and D- data lines.

Very interesting! Though why couldn't earlier iPhones get an update that would have changed the voltage threshold detection on D+ and D- pins, to accommodate new standards? Was is all done in hardware or a seperate microcontroller?

You can limit the output from the charger to the Apple by selecting the right resistors on the data lines.

For full charge 2.1 and 2.6V are used but with that the charger might have to deliver over 1.8A, which I doubt it is cabable off- at least not on AAA's.
Check Wiki for the full specs on USB and what is needed on the data lines:


The section about charging ports is what interests you most.

I think you're right, it is for proprietary reasons. That is what maddens me about Apple, and why I generally avoid their products.

The Lighting connector is another good example of this, where they went through so much effort to avoid using any standardized cable. It is, however, arguably better, since it is reversible, and clearly engineered better. The construction of it is vastly simpler and is more robust, it resembles that of a PCI slot type of thing, rather than the complicated, intricate, (and IMHO stupid) design.

Below is a picture I have found that shows the wiring diagram, everything before the reisistor network is just a jelly bean 7805 voltage regulator, and is not nesseary since reguated 5V is acheived through the boost converter insrtead.