USB emergency charger on 2xAA batteries

Discussion in 'The Projects Forum' started by stepas, Feb 24, 2010.

  1. stepas

    Thread Starter New Member

    Feb 24, 2010
    Hi guys,

    Since i own HTC HD2 cell phone / pda, I would like to build an EFFICIENT portable outdoor emergency charger powered by 2 AA batteries. This cell phone can be charged through USB port, which is 5 volts. I have measured the charging current, and it reaches 900 mA (a lot, huh :) in the beginning, but later current drops below 500 mA. I need to built a step-up boost DC to DC converter from 3 (or 2.4 V in case of rechargeable batteries) to 5V.

    So, I guess I have covered all keywords for future searches whoever will be interested in building one by themselves, so proceed to the point. Also, i am aware of Minty Boost on the net, but I am not happy about their IC (not efficient at current >500 mA), their circuit does not have battery power indicator and the device can not be used to charge the AA batteries. Also, auto-load-disconnect to not available.

    1. So, my first question is which Integrated Circuit (IC) would you recommend, or which IC is most up to date, providing the highest EFFICIENCY at currents of 100 - 1000 mA?

    2. I know that batteries loose the voltage during discharge cycle, so again I have no idea which type of IC will allow to deal with this in a most EFFICIENT way?

    3. Is there something else important to consider when building this type of step-up booster?

    4. I found this Texas Instruments tps61090 IC and many from Linear Technology, but there too many IC available for me to understand which one is the most suitable to start looking at?

    I appreciate your help.