Dual USB Charger With Switching Regulator


Introduction: Dual USB Charger With Switching Regulator

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 suppli...

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

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.



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    40 Discussions

    I couldn't get any cirrent more than 300mA when I charge my phone with the circuit.
    Can You help me find the issue?

    This setting will not work with apple devices with lightning ports

    Am working on a mobile charging kiosk and i need to build a quick charge in a ratio of 1% to 0.5 sec.Is this one going to work for us

    1 reply

    This charger was not made for quick charging phones. It provides up to 2 amps at 5 volts like a typical wall charger.
    If you use a higher current inductor and put a heatsink on the regulator, you can run it up to 5 amps.

    Yes, it will run from car battery just fine. You should put a 2 amp fuse in series with it to be safe though.


    2 years ago

    Sir, can you tell me it can provide the fix 2A 5V power? im trying to do a project which need fix current between 1A to 2A with 5Vdc power supply.

    1 reply

    Are you looking for a constant current power supply?
    This power supply is constant voltage, there is no current limiting other than an overload shutdown in the 6 to 8 amp range.

    can u tell me what amp of input through this devise can give me the out put 2amp

    1 reply

    The input current depends on the input voltage. With a 12v input and 2A load it draws 930mA. At a lower voltage it will draw more current, at a higher voltage it will draw less.

    check the usb female pinout. for charging, pins 1&5 are pos and gnd, pins 2&3 may be shorted with 300ohm resistor but leave pin 4.

    There are some tricks you may have to do with the data lines to get modern devices to charge. Most devices will work with the data lines floating. Every thing I have tried worked fine.

    Some devices need a 200 ohm resistor across the data lines. Apple devices need voltage dividers to provide 2.8v on d+ and 2v on d-.


    I have 12V 3A power supply. Will this circuit work, if I give 12V 3A as input.

    Please Dude help i have a problem the regulator is not available in my country can you sugestt another one ?? thanks :)

    1 reply

    An LM2676 (5V fixed output) should work. It's almost identical, but the maximum output current is 3A instead of 5A.

    LM2678T and STPS10L25D is not available......................................plz tell me alternate lm and diode that i can use

    1 reply

    Can I connect three 3.7 LiPo 1000mah batteries at the input.

    And how much times, this circuit can charge a 1500mah battery within what time.

    1 reply

    Yes, three lithium cells will power it just fine. It should provide almost two full charges. The charging time depends on the charging circuit in your device. It should be the same as when it's plugged into the usb port on a computer.