Thread: A 'possible' AC charger?
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Old 04-11-2009, 10:30 AM   #25
gwynevans
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Quote:
Originally Posted by Stitchawl View Post
I still would like to know 'why' the device can be charged through the USB from a computer but not the USB from a wall charger. The answer "because it can't" is not what I'm looking for. Perhaps we have some electrical engineering folks reading in who can tell me. As I said before, I think it's fun learning new things.
The USB spec includes a negotiation phase which includes specifying the power (current) requirements of the device. While the 'dumb' chargers just make the power available, I'm not 100% sure, but I'm fairly sure that the Sony finds that the negotiation attempt with them fails and declines to draw the power, whereas when used with a real USB controller, negotiation suceededs and battery charging starts.
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