Breaking News
Comments
Newest First | Oldest First | Threaded View
Frozen_One
User Rank
Rookie
re: USB battery charging: itís harder than it looks
Frozen_One   6/11/2013 5:53:04 PM
NO RATINGS
@Duane, yes. My wife's Kindle HD will check to see what the charger can handle and only burden it with that much charging current. When buying a wall powered USB port, shell out more for the higher current model, or be patient and pick up a real book.

old account Frank Eory
User Rank
Rookie
re: USB battery charging: itís harder than it looks
old account Frank Eory   3/15/2012 8:53:22 PM
NO RATINGS
Indeed, backlights are a huge power drain, but so is the RF power amp. CPU-intensive and graphics-intensive activities hurt too, even when running on a low-power processor. I'm not so sure that we will soon be reducing the need for high capacity batteries and large charging currents in portable devices -- in fact, probably just the opposite. New anode materials like silicon nanowires are showing great potential (yes, pun intended!) for dramatically increasing the energy density of lithium ion batteries. They will allow much longer runtimes from batteries that are the same physical size or smaller than those we use today. The corollary to that is a need for even higher charging currents. To charge a battery in the shortest time using the standard CC-CV method, the charging current needs to be near the "C rate" of the battery, and the total charge time will be in the range of 2 to 2.5 hours. For a modern tablet with something like a 6000 mA-hr battery (C rate of 6 amps), you will want a charger that can safely output 6 amps in CC mode. A future battery that has 4x that capacity in the same package size will of course need 4x the charging current if you still want to complete a full charging cycle in a couple hours. Despite the war on current drain in circuit design, the demand for longer runtimes will always be there. The standard for a smartphone today is that it should last all day on a battery charge in normal usage, but all other things being equal (especially size & weight), consumers would be a lot more delighted if their smartphone lasted all week on a single charge...and if still only took a couple hours or so to charge it up again. None of this bodes well for charging from standard USB hosts and their 1.5A current limits.

old account Frank Eory
User Rank
Rookie
re: USB battery charging: itís harder than it looks
old account Frank Eory   3/15/2012 8:35:54 PM
NO RATINGS
Haha, thanks selinz. It's been a great ski season so far, and I hope to squeeze in a couple more days this month before all the snow melts in northern Arizona :)

NielV
User Rank
Rookie
re: USB battery charging: itís harder than it looks
NielV   3/15/2012 7:08:47 PM
NO RATINGS
I think the main reason why portable products need large capacity batteries requiring high charge current is because of LCDs requiring high power backlights to make it usable outdoors. Our company is struggling to find a 7" reflective or even transflective LCD (instead of transmissive) in anything above 5" (e-ink can't be used due to page inversion requirement when updating display). The difference is changing from a 4W backlight to a 0.1W frontlight, but the LCD is not available. Sharp has some nice memory displays starting to address this, so hopefully soon we will not need such large batteries (and charge currents) any more.

Duane Benson
User Rank
Blogger
re: USB battery charging: itís harder than it looks
Duane Benson   3/15/2012 4:28:39 PM
NO RATINGS
Is the typical device smart enough to not over draw from a poorly built charger? Is that something end users need to worry about or are the devices themselves smart enough to not get into trouble with a cheap charger?

selinz
User Rank
CEO
re: USB battery charging: itís harder than it looks
selinz   3/15/2012 3:21:24 PM
NO RATINGS
"Make no mistake: selling specialized accessories is definitely in the business plan for a portable product. " "The idea was to minimize the number of cell-phone chargers ending up in landfills, by converging on one USB-charging specification. " These two sentences are clearly at odds. And Frank, good to know that you are a ski bum! :-)

old account Frank Eory
User Rank
Rookie
re: USB battery charging: itís harder than it looks
old account Frank Eory   3/13/2012 5:56:19 PM
NO RATINGS
Oops, I used an old login. That was my comment above.

Frank Eory
User Rank
CEO
re: USB battery charging: itís harder than it looks
Frank Eory   3/13/2012 5:54:24 PM
NO RATINGS
Good article, although I wish you had gone into more detail on the standard Li ion battery charge cycle of trickle, then CC then CV. It helps the reader to understand the limitations of charging from a USB host -- namely that the max current available for CC mode is less than what is available from a dedicated charger. Even 1.5A doesn't cut it for some of today's mobile devices (e.g., tablets). Readers will still ask why the dedicated charger can fully charge their tablet in 2.5 hours, but when they plug into the USB on their PC, it takes much much longer. You came oh so close to answering that question.



Flash Poll
Top Comments of the Week
Like Us on Facebook
EE Times on Twitter
EE Times Twitter Feed

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Max Maxfield

Energizing the Young Engineers of Tomorrow
Max Maxfield
5 comments
It doesn't seem all that long ago when I was a bright-eyed, bushy-tailed young engineer. Now I feel like an old fool, but where are we going to find one at this time of the day (LOL)?

Jolt Judges and Andrew Binstock

Jolt Awards: The Best Books
Jolt Judges and Andrew Binstock
1 Comment
As we do every year, Dr. Dobb's recognizes the best books of the last 12 months via the Jolt Awards -- our cycle of product awards given out every two months in each of six categories. No ...

Engineering Investigations

Air Conditioner Falls From Window, Still Works
Engineering Investigations
2 comments
It's autumn in New England. The leaves are turning to red, orange, and gold, my roses are in their second bloom, and it's time to remove the air conditioner from the window. On September ...

David Blaza

The Other Tesla
David Blaza
5 comments
I find myself going to Kickstarter and Indiegogo on a regular basis these days because they have become real innovation marketplaces. As far as I'm concerned, this is where a lot of cool ...