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RE: OT: Electronics advice needed to make a combined emergency charger
/ USB supply lead for my PDA
- Subject: RE: OT: Electronics advice needed to make a combined
emergency charger / USB supply lead for my PDA
- From: "Mark A Wright" <mawright@xxxxxxxxxxxx>
- Date: Wed, 14 Jul 2004 18:04:03 +0100
>Where does the -5v come from/why?
-5v my mistake, it was meant to indicate connection to the negative rail.
>You're dropping another (?) 0.7v across D2 to the PDA (what voltage
does
>the PDA expect to see?)
Ahh yes I forgot all about the voltage drop. The PDA should charge a little
under 5v.
>I don't think you can achieve what you want there with only passive=20
>components. Many year ago maplin used to sell a small IC that could
be=20
>used to build a battery backup circuit, they don't seem to have
anything=20
>similar now though. You could try RS and the like.
>Something like this maybe:
>http://www.rohm.com/products/databook/reg/pdf/bd4201fv.pdf
>http://www.maxim-ic.com/appnotes.cfm/appnote_number/190.=20
Thanks I=92ll take a look.
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