5V USB Problematik

The voltage drop budget is determined from the following: ? The voltage supplied by high-powered hub ports is 4.75 V to 5.25 V.

? The voltage supplied by low-powered hub ports is 4.4 V to 5.25 V.

? Bus-powered hubs can have a maximum drop of 350 mV from their cable plug (where they attach to a source of power) to their output port connectors (where they supply power).

? The maximum voltage drop (for detachable cables) between the A-series plug and B-series plug on V BUS is 125 mV (V BUSD ).

? The maximum voltage drop for all cables between upstream and downstream on GND is 125 mV (V GNDD ).

? All hubs and functions must be able to provide configuration information with as little as 4.40 V at the connector end of their upstream cables. Only low-power functions need to be operational with this minimum voltage.

? Functions drawing more than one unit load must operate with a 4.75 V minimum input voltage at the connector end of their upstream cables.

D.h. mit einer Diode, die knapp 350mV Vf hat, geht das noch so gerade (ohne externes Netzteil ist das ein "bus-powered hub", der nur 100mA pro Port

"low-power bus powered".

cu Michael

Das war z.B. bei meinem Dell XPS8700 der Fall. USB-Centronics Wandler besorgt, Drucker angeschlossen, lief, juchheissa! Morgens verweigerte der PC den Start, bis ich entweder den Wandler, den Centronix Stecker am Drucker oder den Netzstecker der Druckers herauszog (Netzschalter hat er nicht). Es kam "rueckwaerts" ueber den USB Stecker Saft.

Dann sollte der Entwickler der geschaedigten Hardware kurz in den Burggraben getunkt werden, damit er es beim naechsten Projekt besser macht.