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Phone Charger Using A 7805 Voltage Regualtor

I recently replaced my Blackberry Curve with a Verizon Incredible. I soon found that the battery life was the only thing that wasn’t incredible about the phone. Owning a smart phone like the Incredible, Droid X, Apple iPhone or even a Windows Mobile is a paradox; because the more you use the phone the quicker the battery drains. Newer smart phones make the phone more useable than ever before, which means after a few hours the phone is dead.


There are a couple ways to tact the problem of battery drain in smart phones. The first is to carry a spare battery around with you. The problem with that is the batteries are expensive, if the contacts touch metal you will start a fire. Also once you’ve discharged both batteries, its back to the battery charger in the car or home to charge two batteries now. Oh and to charge the extra battery you need to put it in the phone, which mean twice as long on the charger.

I recently seen a solar charger for the cell phones, the problem with that is the phone needs to be in the sunlight which also means the extreme heat from the sun. The Incredible suffers from heat charging where if the battery gets too hot it will stop charging and trip the phone out. I overheated my phone a few times while I was travelling in the heat. The Incredible will flash green and orange while on charge to signal overheating.

The last option I seen in an airport is called “The Charging Station”. It is a booth with every adapter known to man and a credit card slot. You buy time to charge your phone; the problem is you need to be tied down to the charging station while it’s being charged.

I knew that I would be using my phone a lot on the last trip I went on, so I wanted to make sure it wouldn’t go dead on my journey. My plan was to make my own Minty Boost from spare parts in my office. A Minty Boost is a small device that uses “AA” batteries and a step up converter, to step the voltage up from 3 volts to 5 volts.

About the Circuit

My plan was to step the voltage down from a 9 volt battery to 5 volts using a 7805 voltage regulator. Two 100uf electrolytic capacitors are used to buffer the voltage for any line noise. They are placed in front of the 7805 and in back. These capacitors are not “required” for use with a 9 volt battery since there is no noise (transformer) that would come from the battery itself. This circuit can be adapted for an old DC transformer so I left them in the schematic. The ceramic 100nf cap is to buffer the voltage during load changes and should be kept in to provide a smooth 5 volt supply.

Phone Charging Circuit 7805

Construction

I didn’t do anything fancy like etching a PCB, I just used some fabrication board and soldered the leads together. I also took apart an old USB hub and desoldered the female USB A-type connector. The USB connector fit nice on the fabrication perf board. I did use some epoxy to firm it up against the 7805, which worked out well because it acted like a heat sink. Of course I packaged the whole thing in an Altoids mint container that I had lying around. I used double stick tape to mount the board in the mint container and used a Dremel to cut the opening square.

Perfboard fabrication and testing before the case

Charging Curcuit fit into Altoids Case

Detailed top view of the charging circuit fit into the Altoids case

Final testing of design with my old curve.

Now anytime I’m out and need a quick charge as long as I have the box in my bag, I can always find a 9 volt and charge my iPod or Incredible back up. During the trip I used it with great success and got an average of two full charges out of a 9 volt battery.