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
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
Protoboard or PCB
LED & Resistor (Optional)
Step 2: Build the Circuit
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
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
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 can run at full power for over 2 hours off 8 AA rechargeable batteries, or 8 hours charging 1 device at 500mA.