car 12v phone chargers

Charging time will depend on the current and not the voltage. I'll guess that the 12V auto charger just has a linear regulator.. (not a switcher) and so to do (say) 1 amp at 5 Volts it would need to dissipate 7 or 8 watts... that's too much so they cut dwon the current.

Just a guess, George H.

They probably have a switcher these days - the really cheap crappy plastic case would deform with the heat from a dropper resistor inside.

even safe to use - I was going to pick one up to crack open to see what's in it, but they were out of stock and I don't go into town that often.

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I needed a USB charger recently, and thought of buying one of those cheap= =20 small cubes. And I decided I wouldn't trust it (not the cheap kind)=20 unless I did open it, and then I decided I wasn't so curious that I'd want= =20 to buy the thing twice, one for looking and then another for actual use if= =20 it looked safe.

I admit they were cute and compact, but I just used a 5v AC adapter=20 (switching kind) that I'd pulled from somewhere, and wired on a USB jack I= =20 desoldered from a scrap motherboard. Not as neat, but I trust it.

Michael

The ones I've looked inside have some sort of DIP8 based switcher... I've not tested the max output current,

If you're that wary, build a breakout box to contain a SCR crowbar protection.

A common type is the MC34063 - its actually hard to find versatile switcher chips that don't have UVLO at a lower voltage than you want to run it from.

charging connectors.

I'll crack it open for a look inside later.