Daniel Jonsson said the following to all on the subject of
Voltage change (23 May 97  11:54:17)
 DJ> A friend of mine have a USR Sportser wich transformer he unluckily
 DJ> destroyed. Being desperat he replaced the transformer with a one wich
 DJ> hade 3V more then the first (or vice versa, 3V less...).
 DJ> I thought the modem wouldn't work/burn, but to my suprise it worked as
 DJ> well as ever. Can someone explain why?
 DJ> Cheers Daniel - sorry about my grammar.
From what I can determine, these modems have an onboard switching supply
using the TL494 switching regulator control circuit. Switching
regulators can tolerate a wide range of input supply voltages.
Typically in a switching supply the series-pass transistor will generate
more heat at lower input supply voltages. Because of this PC supplies
more often breakdown when a power line brown-out occurs.
However in this modem the pass transistor is amply over-rated and
therefore doesn't seem likely to fail at low input supply voltages.
Your friend may rest assured that a 3 volt difference is probably not
too critical in this case. I use a 12vac wall pack but the modem will
probably work just as well on 9vac.
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