Introduction: Dual USB Charger With Switching Regulator

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About: I enjoy building electronics & robots. I like building computers as well as writing programs & web sites. I like to build and launch rockets. I especially like to play with high voltage power supplies…

This is a portable USB Charger. It uses a high efficiency switching regulator that runs at 85 - 94% efficiency depending on input voltage and load.
It takes an input voltage from 8 to 16 volts and can run from anything from a 9 volt battery to a car battery.
It has 2 USB ports and easily charges 2 power hungry devices at once. 

Step 1: Parts & Tools

Parts

LM2678 - 5V Switching Regulator
STPS10L25D Schottky Diode
22µH 5A 15mΩ Inductor
470µF 16V Electrolytic Capacitor
120µF 16V Electrolytic Capacitor
100nF Film Capacitor
10nF Ceramic Capacitor
Dual Type A USB Jack
5.5 x 2.5 mm Barrel Jack
5.5 x 2.5 mm Barrel Plug
3x2x1" Project Enclousure
Slide Switch
Protoboard or PCB
LED & Resistor (Optional)

Tools

Soldering Iron
Dremel
Wire Cutters
Needle Nose Pliers
X-Acto Knife
Screw Driver

Step 2: Build the Circuit

When building this circuit you need to keep the lines as short as possible to keep it running stable and efficient. The feedback line should be kept away from the inductor.
A PCB would be best for this circuit (although I used protoboard)
I cut the circuit board down to fit the box with a Dremel.

Heat doesn't seem to be a problem.
The diode runs cool, and the regulator runs about 50°C with a 2A load.
The regulator has built in over current and thermal protection. 

The LM2678 can supply up to 5 amps but the circuit here has been optimized for 0.5 to 2 Amps.

Step 3: Put It in the Case

I had to make room in the project box by sanding off the circuit board holders on the sides.
Cut out a slot for the USB ports and the power jack.
Cut out a hole for the slide switch.
I used a Dremel and X-Acto knife to make the holes. 
I mounted the board with hot glue. The switch and jack are also glued in place.
I put a 3 mm blue LED in the lid.

Step 4: Finish It Up

Put the lid on and make a nice label.
Touch up the screws with a sharpie.
Put together a power cord.

Check the output voltage, it should be very close to 5 volts.
The USB standard specifies 4.75 - 5.25 volts

This charger can run off  a battery pack, AC adapter, or the 12v power port in the car.
It will be most efficient at 9 -12 volts. And it will draw about 1 Amp at full load.

Step 5: Using the Charger

The charger has no problems charging my phone or my Archos 5.
The charger can run at full power for over 2 hours off 8 AA rechargeable batteries, or 8 hours charging 1 device at 500mA.