Bose SoundDock 10 Service Manual page 71

SoundDock 10 Theory of Operation
SoundDock 10 Theory of Operation
SPS Board
AC Connector (J400)
The AC Connector is our standard polarized connector with enclosed leads. Care has
been taken to put extra holes in the board to increase spacing from line to neutral and to
expel liquids should they be spilt on the board.
Line Filtering
The line filtering is comprised of a common mode chokes (L400), 4 150pF Y capacitors
(C400, C402, C406, and C407), an X capacitor (C404). These components work to
reduce conducted (and radiated) emissions. C404 is especially critical in reducing the
192kHz switching frequency differential mode emissions. The Y caps and common mode
choke work together to reduce common mode emissions.
R403, R404, and R407 are there to dissipate power and reduce the voltage seen at the
AC connector after AC power is removed.
VR402 is used to suppress line surges and especially protects C404. If the line surge is
large enough the fuse (F400) will open before anything is damaged.
Fuse (F400) and NTC (RT400)
The fuse is a 4A rated slow blow fused. It was chosen for its high I^2T value to avoid
false tripping due to spurious line spikes etc. The NTC provides inrush current suppression.
Bridge Rectifier (BR400)
BR400 is a standard thru-hole bridge rectifier. It is easily able to dissipate just over 1W of
power under worst case conditions.
Voltage Doubler or Auto Switch
The Auto Switch components are only populated in the dual voltage variant which looks at
the AC input line voltage and decides if it should double this voltage (< ~160Vac) or not.
In countries where the input voltage will never exceed 160Vac, the circuit is configured to
always double the input voltage. The dual voltage systems can be used in any country,
however it was decided that it was not cost effective to populate the auto switch
components in countries where the line voltage always stays within a certain range.
The voltage doubler works by charging each bulk cap (C409 and C410) one half cycle at
a time. It works by applying a short at JP401. Note that in this configuration only 2 of the
4 diodes in the bridge rectifier are used.
The Auto switch looks at the input line voltage at pin 8 through the R406, R409, R410/
R405 resistor divider to determine if it should double the voltage by turning on the triac
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