This keeps getting asked, so I'll wade in . . .
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Warning: High EE Nerd Content -- Reader discretion advised
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To be sure of the tolerances, you'd need to look at the chip specs for charging. I'm Sorry but I'm not taking mine apart to read the board and chips to find the charger/regulators on the unit and looking up their data sheets. I like you guys, but that's too much like real work
Anyways, 5.2v out of a USB port is not uncommon, and it wouldn't surprise me to find Sony's 5.2v adapter running 5.3, 5.4 or more(!) when it's disconnected. Most of those voltage ratings are for "under load" and depend on how well the adapter is regulated. If you're using an AC/USB or DC/USB adapter, they're probably close enough in voltage and regulated well enough for your reader.
Either way, I'd worry much more about over-voltages than under-voltages -- over can burn out circuitry, while under usually robs performance (in this case charging slowly or not at all). It's possible for under-voltage to damage circuitry, but my knee jerk reaction is that 0.2v under makes a slim chance for it.
Do watch the amp rating -- but you're probably still fine. The Amp rating is usually a measure of current that CAN be drawn at the stated voltage. Draw less, and no one cares (after all, with the device unplugged, you're drawing 0 amps and the adapter doesn't seem to mind).
Try to draw more than rated and you can have source overheating and/or voltage dropout (severe under-voltage). The failure modes for over-current depends on how the source and target hardware are set up, but are usually either fail catastrophic
, fail safe
or fail gracefully
. Only catastrophic needs to be avoided at all cost.
What I would do to avoid the catastrophic failure: Check the temp of the AC/USB adapter after 15-30s and again after a few minutes(I'd also check the charge lamp on reader). If the charge lamp is on and the adapter is not getting above slightly warm, your charging setup should be stable.
If the adapter is getting hot, unplug it immediately -- you're over stressing it and it can burn out or burn up(Fire!).
Of course, if the lamp isn't coming on you aren't charging (fail safe
), but check also that the charge indicator does go up over time (IIRC, you'll have to unplug it to see).
From my experience (again, I haven't ripped open the case to look at the chips), the Sony readers fail gracefully by throttling back the current it demands as the voltage begins to drop. This matches mine and others experiences that the unit still charges, the adapter doesn't overheat, but the process takes longer.
Dan <><