At 05:54 PM 11/11/2010, V G wrote: >Hi all, > >I'm looking to build a simple battery-powered charger for my mobile >phone. I'm out a lot where it's not convienient to plug my phone into >a wall outlet. > >The charger will simply consist of a power supply that provides 5 >volts via a USB socket. I want to power it with 4 AA NiMH batteries >(Sanyo Eneloops). 1.2 * 4 =3D 4.8, so I will need to use a boost >converter of some sort to output 5 volts. My experience has been that you don't need any electronics at=20 all. Inexpensive battery-powered USB chargers that I have purchased=20 confirm this. Both NiCd and NiMh batteries have a very flat discharge slope. The=20 terminal voltage ranges from about 1.25V (fully charged) to about=20 1.1V (less than 10% charge remaining). That means that a 4-cell pack=20 will range between 4.4V through 5V. A standard USB port will supply somewhere between 4V to 5V under load. Take note that you should NOT ever use alkaline batteries in your=20 box. One of the battery-powered USB chargers that I purchased took=20 care of that possibility in a typical Far East fashion: they had 3=20 large (5W?) 5.1V zener diodes connected in parallel right across the=20 battery pack. The obvious intent was to force alkaline batteries to=20 discharge quickly so that the terminal voltage was less than the zener volt= age. Bottom line: a small battery pack with 4- high-capacity NiMh=20 batteries should be all that you need. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .