iPhone USB Charger for use with a 9v battery
There have been a few how-tos on the net, for making a simple USB charger to power up your USB chargerd mp3 players and satnavs in an emergency. They’re all well and good, but they won’t work with the newer iPods, or iPhones because they expect not only +5v and Gnd, but additional voltages on the other 2 USB pins.
The ideas behind these charges are very good, so why not build on them, and make them better? Well, I did just that. For the princely sum of about 4 euro, and using off the shelf components from Maplin, I had this wired up and charging in about 10 minutes. For the build you’ll need a 9v battery clip (Get the hard plastic ones, not the flexible plastic type), a 7805 voltage stabiliser, a female USB A port, and 4 100 Ohm Resistors. I know the 7805 will get hot during prolonged use – so please don’t eMail me telling me that. This is an emergency charger, not an everyday item.
This is the circuit from start to finish. The purposed of the 7805 stabiliser is to take the voltage from the battery (9v, dropping off as the battery dies), and convert that to a stable 5v output. The resistor bridge will then drop that 5v to the required levels across pins 2 and 3 to activate charging on the iPhone/newer iPods.
And here are the components. Nothing too scary here.
To get the physical form factor of the charger setup, glue the 7805 on to the top of the 9v battery clip, and then glu the usb charger onto it. You’ll end up with this column of components.
Here it is from another view
The rest is simple soldering, using the diagram above solder the various connections in, and the resistors across the pins on the USB port. Because the length of cable on the battery clip is so long, you can clip this short, and use the leftover cable for short runs between parts. Test everything with a multimeter, especially output voltages, and you’re ready to hook your USB device into this and start charging. Easy!