Introduction: Dual USB Charger With Switching Regulator

Picture of Dual USB Charger With Switching Regulator

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

Picture of Parts & Tools

Step 2: Build the Circuit

Picture of 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

Picture of 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

Picture of 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

Picture of 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.


chinocrix (author)2017-09-29

This setting will not work with apple devices with lightning ports

discovery20720 (author)2017-05-18

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

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.

CYBERJ_21 (author)2016-10-18

can i use 12v car battery as my input??

rocketman221 (author)CYBERJ_212016-10-18

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

JieE2 (author)2016-03-30

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.

rocketman221 (author)JieE22016-03-30

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.

musharaf raza (author)2016-02-29

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

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.

kotosif (author)2014-07-06

Does this instructable work with modern smartphones? Such as S3 or Iphone?

vashteusen (author)kotosif2015-05-10

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.

rocketman221 (author)kotosif2014-07-07

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-.

aswinmp (author)2014-09-25


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

RoMaNs.2012.H (author)2014-09-18

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

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

jerry mughal (author)2014-06-20

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

The diode is back in stock now, and the regulator is available here.

yooooo1089 (author)2014-06-20

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.

rocketman221 (author)yooooo10892014-06-20

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.

jerry mughal (author)2014-06-17

hi rocketman i want to use this circuit to charge my galaxy this circuit will work........plz repaly

jerry mughal (author)2014-06-03

hi buddy plz can u upload a video of this circut

ToXiCATOM (author)2013-06-12

can I use 12v 10A RMS to power it up?

rocketman221 (author)ToXiCATOM2013-06-12

Yes, It will run from 12 volts. With a 2A output, it will pull just under 1A from the input though.
If you intend to run it from AC, it will need a bridge rectifier at the input and a larger cap for C1.

monkizzle (author)2012-08-20

the link for the 10nF Ceramic Capacitor point to the same thing ask the 100nF Film Capacitor. Does anyone know the right digikey product number for the 10nF Ceramic Capacitor?

rocketman221 (author)monkizzle2012-08-20

The link is fixed now.
478-4862-ND or any 10nf ceramic cap will work.

luketanti (author)2011-01-18

Hi Nice instructable!! I am planing to make a power supply for and old computer (Intel celeron 553Mhz) and wish to use this as the main 5v supply. I will connect this to a car battery. To use the full 5amp usage do I have to adjust the circuit please??

rocketman221 (author)luketanti2011-01-18

For a full 5 amps you need a different inductor.
Use a 10uH inductor with a current rating of 10A or more.
Digikey # 732-1418-ND would work.

It also needs a larger output capacitor 330uF would work.
The diode will need a small heat sink, the regulator might need one too.

If you are running it from a car battery be sure to put a fuse on the battery.

That's Digikey part number M1400-ND Not 732-1418-ND

luketanti (author)rocketman2212011-01-19

Thanks Very Much. I'll try with those changes.

luketanti (author)luketanti2011-01-24

Hi. I tried with those specs you said and my voltage output is 8.5v to 9v. I am sure I have the 5 volt version. What could be wrong. I tried it with a pc power supply from the 12v rail. I think the output voltage should be nearly 5 volts right? Can some on help please.

luketanti (author)luketanti2011-01-24

Another thing is I found another circuit similar to this bu instead uses 22uh inductor and 4 extra capcitors. It says that it is good to give 5 amp.
here it is.

luketanti (author)luketanti2011-01-24

I am sorry to replay again but I want to tell you that I tried a different inductor. Instead of 10uh I used a 22uh and now the voltage with no load is 6.5 volts. When I connect a small fan the voltage goes down to a steady 5 volts just as I want and I thought it was ok but when I tried to connect a wireless bridge rated at 5 volts 1 amp the voltage went down to 2.5 volts. What is the matter it. Can you help me please. Could the diode be the cause. I am using a 1N5818 diode because I can not find to buy it in my country. Thanks.

rocketman221 (author)luketanti2011-01-24

The 1N5818 diode you used is only rated for 1 amp, and has a drop of 550mV to 875mV.
The diode I listed is rated 10 amps and has a 460mV drop.
Try to find one with similar ratings. The lower the voltage drop the better.

The schematic you used it fine. The inductor should be toroidal otherwise it creates interference, in that case the feedback line should be kept away from the inductor.

Switching power supplies need a load, mine seems fine with just 10mA from the LED. With a load the power supply should be 4.9V - 5.1V

luketanti (author)rocketman2212011-01-25

I replaced the diode with F5KQ60 and added an LED with the output and not the volatge with no load is between 5 volts to 5.5 volts. That is acceptable. But now the new problem is when I apply a load of more than 120mAh the voltage drops instantly to 3.4 volts. I can not find the cause may be you can help me?
Thank you very much. You have help me alot.

rocketman221 (author)luketanti2011-01-25

The diode should be OK.
What is the current rating on your inductor. For a 5A output it should be rated at least 10A.

luketanti (author)rocketman2212011-01-25

The inductor is from coilcraft Part number is DO5040h-223MLB. This is the specs
Inductance 22uH
DCR max (mOhms) 24
SRF typ (mHz) 13
Isat (A) 11.8
Irms (A) 5.7

And I am noticing that the output capacitor 330uf 16v is getting bloated. I do not know why. This is the second one I changed and the same results.

rocketman221 (author)luketanti2011-01-25

Make sure the output capacitor is connected the right way. They will bulge out if the are put in backwards or are run at too high of voltage.
The inductor should be fine although it might get warm.

How is the circuit layout? Some of the lines should be kept short. (refer to the diagram)

luketanti (author)rocketman2212011-01-27

Thanks very Much!! I had connected the out capacitor with pin 6 instead. That is why it got bulged. Now it works perfect. Exactly 5V output and can supply 5 amp.
Thanks again!!

alfredhenriksen (author)2010-08-28

i liked it! The cool thing is that if you've only got a 16V/1A supplier, the output amperage can be higher than 1A. I have played a little with LM2576, and became surprised when I got 4.16A out of it. PS: Why does it get 3.09 in rating when I rated it as 5.0, and I am the first one to rate it? "3.09 (1 ratings) Your rating: 5.0"

About This Instructable




Bio: 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 ... More »
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