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Old March 18th 17, 04:50 AM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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On 3/17/2017 10:55 PM, jbeattie wrote:
On Friday, March 17, 2017 at 7:00:01 PM UTC-7, Frank Krygowski wrote:
On 3/17/2017 8:00 PM, Joerg wrote:
On 2017-03-17 13:53, sms wrote:
On 3/17/2017 12:58 PM, Joerg wrote:
On 2017-03-17 12:11, sms wrote:
On 3/13/2017 12:28 PM, Joerg wrote:

snip

You could stick in a Murata LXDC55FAAA-203
http://power.murata.com/data/power/LXDC55FAAA-203_data_sheet_E.pdf
instead of the zener and do a USB version also with only three parts.
But I know that you love designing your own switchers.


$3.50? Mon Dieu! :-)

I got some of the Murata LXDC55FAAA-203 units from Digikey for use at
work. I guess I didn't realize from the picture on the data sheet just
how tiny these things are. Maybe I'll buy some more and try building
some dynamo to USB adapters.


Be carful with that 16V abs max input limit. When the load current drops
this can easily be exceeded by a dynamo, big time. You could burn off
the excess with a zener diode or TVS (though _not_ MOV) but these have
large tolerances and could burn out if not well heat sinked.

I think you need somthing automotive here, some circuit that can stomach
50V or more.

I'd just stick a 15V 5W zener in there for the rare times that the
dynamo is exceeding 11VAC. If I were going to sell these I'd do
something more robust.


And then you have to cool that zener. And hand-pick one because of
tolerance. Also, those things are soft. Better to build an "active
zener" with a TL431 and a transistor. However, I'd prefer a switch mode
regulator that can handle north of 50V because then you can capture all
the juice generated on that long downhill section. I have a few of those
when riding into towns west of here. On the way back, of course, it's
sweating and suppressed cussing because those 1000+ feet have to be
gained back.


If you're trying to charge USB devices, you should at least look at this
design:

http://fahrradzukunft.de/12/minimal-lader/

It seems to be much simpler than what you're considering.


I use this device: http://images.wisegeek.com/standard-us-power-outlet.jpg


It's not very portable.



--
- Frank Krygowski
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