9v and Double A iPod Charger

Ideas and questions about MintyBoost kits

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Zava
 
Posts: 1
Joined: Thu Jul 12, 2007 11:05 pm

9v and Double A iPod Charger

Post by Zava »

I was considering making a two in one ipod charger - one that would use this circuit to boost up 2 double a batteries to 5v if I had those on hand, or, if I had some 9v batteries on hand, use the 7805 linear regulator to bring it down to 5v. I know I could put in a manual switch to go between these two; however, I was wondering whether anyone had any ideas for a circuit which would send it through the linear regulator if it was over 5v, and through the boost chip if it was under 5v. Thanks!

Illuminum3415
 
Posts: 21
Joined: Fri Jun 22, 2007 12:11 pm

Post by Illuminum3415 »

aside from a circuit what about a SPDT switch that connects the positive end of the 7805 and the minty boost to two of the posts and manually select which type of cell you use when you use it. just add Schottky's to the output of the 7805 to prevent back feeding when one system is on and not the other.

9V + 7805 is a relatively poor system though...your looking at 4 watts of heat which is enough to give 2nd degree burns and enough to melt solder off the IC...I know because I've built numerous 7805 charger prototypes and wind up sealing the 7805 in a jar of deionized water to cool it long enough to charge up any useful amount of runtime.

if you prefer to use 9V as power sources anyway, consider the MAX738, LT1173 or LT1120 ICs

If you want...you can go to radioshack and buy some PC boards, locate some samples of 1173s from linear tech and build both the step up and down on a single platform.
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