Messages in this thread | | | Date | Thu, 15 Sep 2016 12:33:52 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation |
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Hi!
> > That's not actually 100% clear to me - for what the wm831x is doing it > > probably *does* want the higher limit. This is a system inflow limit > > (as it should be for this), at least the charger will adapt to voltage > > variations though other users in the system are much less likely to do > > so. > > Interesting ... I hadn't considered that possibility. > > As long as the current remains below the maximum, the charger will > reduce the voltage towards 2V as load increases. Somewhere before it > gets there, the system will not be able to make use of the power as the > voltage will be too low to be usable. So that will naturally limit the > current being drawn. > > Not having very much electrical engineering background, I cannot say for > sure what will happen, but it seems likely that once the voltage drops > much below 4.75V, the charger won't be operating at peak efficiency, > which would be a waste. > I can easily imagine that the hardware would switch off at some voltage > level, rather than just making do with what is there. > So I'm skeptical of this approach, but I'm open to being corrected by > someone more knowledgeable than I.
Devices I seen charge down to ~4.2V. This is useful thing to play with:
dx.com: 406496 1" USB Current & Voltage Detector Tester Meter w/ Red LED Display - Blue
Best regards, Pavel
-- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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