The mini and micro connectors have an extra "ID" pin that's grounded for A, and open for B, to tell the device whether it's supposed to be in host mode.
...found mc34063A chip inside! It is a switching power supply with a 1.5A rating, and a 40V input tolerance!http://html.alldatasheet.com/html-pdf/92977/STMICROELECTRONICS/MC3463/1620/1/MC3463.html
Quote from: cyclegadget on Jul 04, 2012, 04:17 am...found mc34063A chip inside! It is a switching power supply with a 1.5A rating, and a 40V input tolerance!http://html.alldatasheet.com/html-pdf/92977/STMICROELECTRONICS/MC3463/1620/1/MC3463.html Update, I removed the female USB connections and the bits that connected to the cigarette lighter and soldered on wires in their places. I tested it with a good adjustable power supply going to the input and no load on the output although, I think the circuit has a small load resistor on it. Results = 7v to 25v input = 5.01v output. Not bad at all. Input < 7v makes output below 5v and somewhat unpredictable.
A dollar tree is clearly not what I thought it was.
My reading of the Wikipedia USB suggests that A and B are form factors, not having anything to do with host mode. Maybe there's a convention for host using A and non-host using B?
It's more than a convention: it's a standard, like RS-232.