Gabriel said:
If I have a usb mp3 connected by a usb cable and the pc is in standby mode
or is totaly off will the pc drain the mp3 players battry?
Thanks
GK
There is no way to know that for certain. It might depend
on the cheapness of the design.
The first item I got in a search, was an EDN article. This
is a picture from the article.
http://www.edn.com/contents/images/185954f1.pdf
That shows three circuits total. First circuit,
with the MAX1811, converts Vusb to Vlithium_battery.
The other two, derive operating voltages later,
for operating logic ICs in the player, using Vlithium_battery
as the source.
If we download the MAX1811 datasheet, it gives an example of a
battery charger.
http://datasheets.maxim-ic.com/en/ds/MAX1811.pdf
Input Supply Current (from USB) Shutdown, EN = GND 6 µA
BATT Leakage Current
(Input Power Removed) VBATT = 4.2V, IN = GND 10 µA
The 10 µA number is the one we'd be worried about. If the battery
pack was 100maH, then divide 100 / 0.01 to get the hours before the
battery pack is drained by the charger chip. That is a bit more
than a year. The losses of the battery itself, could be worse
than that. That second figure, takes into account an operating
condition where "IN = GND", which might be apparent if you
leave the MP3 plugged into the computer, then kill the power
via the switch on the back of the computer. That would give
approximately "IN = GND". If you unplug the player, the
leakage could be a number less than 10uA. To keep that level of
current in perspective, that is about 5 times what a digital
watch draws, or about the same amount of current as the RTC
in your computer draws, to run the digital clock that keeps
time when the PC is powered off.
There can be all sorts of failure modes, related to portions
of the player drawing current, after it has been "turned off".
That is as likely a failure mode, as the charger chip providing
a reverse path to drain the battery. And the batteries aren't
exactly champs either, as lithium gets old fast. A good reason
for the battery to be user replaceable (if someone at Apple was
listening).
Paul
