DIY-battery-powered-usb-travel-charger-introduction

Battery powered devices are all around us in daily life and we always face with low charge problems which lets us down in the middle of the day. Especially phones, music and video players, e-book readers etc. Sometimes we can’t find a mains source to plug an AC adapter or an USB port of a computer. In those cases, the battery powered USB travel charger comes to aid. It can be powered by two or three AA or AAA size batteries which you can find easily or carry with you while you are mobile.

This article provides all the steps of the design and the manufacturing process of DIY Battery Powered USB Travel Charger project.

Circuit Design

There are various types of batteries in the market. The main two categories are primary (non-rechargeable) and secondary (rechargeable) batteries. Non-rechargeable batteries are also called “Single-Use” or “Throw-Away” since they cannot be used or recharged after they run empty. They are mainly categorized as Carbon-Zinc, Alkaline and Lithium depending on their internal chemical structure.  Rechargeable batteries as their name implies, they can be recharged for reuse.  The types of this kind are Rechargeable Alkaline, Nickel-Cadmium (Ni-Cd), Nickel-Metal Hydride (MiMH), Lithium Ion and Lead Acid. All those batteries have different output voltages which range from 1.2Vdc to 1.5Vdc.

schematic

To power our charger, we will use two NiMH rechargeable batteries in series which will results 2.4Vdc. Since we will make a USB charger, we need to get 5Vdc and 500mA output from the circuit. This means we need a DC-DC Step-Up converter which will convert 2.4Vdc to 5Vdc and capable of supplying 500mA continuously. When we search for the products of Step-Up converter IC manufacturers, we see that LT1302-5 from Linear Technologies best suits to our needs. The main features of this Fixed 5V DC/DC Converter IC are;

  • 5V at 600mA from 2-Cell Supply
  • 200uA Quiescent Current
  • Logic Controlled Shutdown to 15mA
  • Low VCESAT Switch: 310mV at 2A Typical
  • Burst Mode Operation at Light Load Current Mode Operation for Excellent
  • Line and Load Transient Response
  • Available in 8-Lead SO or PDIP
  • Operates with Supply Voltage as Low as 2V

Assembly and Test

The part list is given below. They are all SMD components so you need to have intermediate level of soldering skill. You can easily find and order the components from Farnell, Digikey, Mouser etc. At DealExtreme you can find various battery holders such as 2xAA, 3xAA, 2xAAA, 3xAAA, with cover or without cover, with switch or without switch etc. It should be better if you have a battery holder with switch, but if you don’t, no problem since the quiescent current of the circuit is extremely low which is about 200 micro amps.

bare-boards-620

Part List

  • 1 x LT1302-5 Fixed 5V DC/DC Step-Up Converter
  • 1 x MBRS130LT3G Schottky Diode
  • 1 x MSS1260-103ML 10uH 3A Power Inductor
  • 2 x 100uF 10V C or D-Case Tantalum Capacitor
  • 1 x 0.1uF 63V 0805 Case Ceramic Capacitor
  • 1 x 0.01uF 63V 0805 Case Ceramic Capacitor
  • 1 x 20K up to %10 0805 Case Resistor
  • 2 x 75K up to %10 0805 Case Resistor
  • 2 x 50K up to %10 0805 Case Resistor
  • 1 x 2xAA, 2xAAA, 3xAA, 3xAAA Battery Holder

The assembled circuit board is shown below,

assembled-board-front-view-620

assembled-board-back-view-620

It is time to test the board. We need two AA size batteries since the battery holder is 2xAA. In this step, we used two different batteries. GP 2700 Series 2600 mAh rechargeable battery and Duracell MN1500 Alkaline non-rechargeable battery.

gp-2700-and-duracell-mn1500-batteries-620

Figure 5 – Gp-2700 Series 2600mAh rechargeable batteries

Fully charged GP 2700 batteries could charge 85% of iPhone 3GS’s internal battery. And Duracell MN1500 batteries could charge only 20% of the same battery.

Fully charged GP 2700 batteries could charge 90% of LG Optimus E420-II. And Duracell batteries could charge 25% of the same battery.

phone-charging

Figure 6 – Charging LG Optimus E420-II

Fully charged GP 2700 batteries could charge 100% of the battery of Amazon Kindle twice. And Duracell batteries could charge 50% of the same battery.

charging-kindle

Figure 7 – Charging Amazon Kindle

Considering the test results, it is obvious that we should use rechargeable batteries to be able to get a significant charge percentage.The capacity of those rechargeable batteries also plays an important role.  On the other hand, the circuit lets an input voltage less 5Vdc. So we can use 3xAA or 3xAAA batteries which provide 1.2V nominal output voltage. This time we will need a larger battery holder.
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