Bose SoundDock 10 Service Manual page 76

SoundDock 10 Theory of Operation
is set by R505. The sync pulse, when applied through the DSP to OL_PS_SYNCH_CLK,
sets the output switching frequency to 192kHz.
Peak Detect Circuitry
This circuitry peak detects the output of the isolation pulse transformer on the primary
side and uses the absence or presence of pulses to shift a threshold in the PWM
controller. When the sync pulses are present (either through OL_PS_SYNCH_CLK or
BIGMAX_OFF), Q508 turns on which in turn switches in R556 in parallel with R508. This
shifts the DC set point of Isense which effectively switches the threshold at which the
PWM controller enters pulse skip mode. We do this to ensure that the PWM controller is
not in pulse skip mode when the power amps are on. This is done to avoid both acoustic
noise from the transformer itself caused by pulse skip mode (the amount of this noise is
proportional to the load) and noise created from the beat frequencies of the power amp
and power supply switching at different frequencies.
The power supply is required to be in pulse skip mode in low power mode to reduce the
power drawn from the wall by reducing switching losses. Acoustic noise from the
transformer is less of a problem in this mode because there is less current through the
windings of the transformer. We also pot the transformer to reduce the acoustic noise
emitted in this mode.
Quick Half Bridge Details:
Input voltage range 212VDC (75Vac (Japan low line) *2 *1.414) to 423VDC (299Vac (India
high line) * 1.414)
Turns ratio, magnetizing inductance, leakage inductance (30/11/7, 220uH, 5.3uH)
Output inductor value 28.75uH
Output capacitor value 3300uF
DC blocking capacitor value. .1uF
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