Power Amplifiers - Bose Companion 5 Service Manual

Power Amplifiers

Power Amplifiers
The Phillips TDA8566 power amplifiers (U150, U250, U350) provide 26dB voltage gain and the capability to drive
speakers with 2 to 4 Ohm DCR. The Equalization for the system requires the amplifiers to drive to approximately
9.5 volts peak. Thus a 450 millivolts peak input is sufficient for the system to generate the peak audio power
required.
The power amplifiers each have an open collector output from their clip detection circuitry that is active whenever
either of the output transistors are saturated. The DSP monitors the status of clip detect for U150.11 via the
CCLIP\ signal. U150 drives the inner (center) transducers of the left and right speaker arrays. U250.11 and
U350.11 are both connected wire-or to the DSP via BSCLIP\. U250 drives the "B" coil of the bass transducer and
the outer (surround) transducer of the right array. U350 drives the "A" coil of the bass transducer and the outer
transducer of the left array.
Mode
The MODE input on pin 20 of the devices mutes the power amplifiers when the potential at the pin is between
3.3 and 6.4 volts. When muted the power amplifiers remain biased and the outputs active. The power amplifiers
are active when the MODE input is above 8.5 volts. If the MODE potential is below 2 volts the amplifiers will be
placed in stand-by. In this condition the internal bias for the amplifiers is turned off and the outputs are not
active. Companion 5 does not use this state. During system stand-by, the Vraw power supply is turned off.
Transistor Q450, resistors, R451 and R453, and Zener D450 convert the MUTE signal from the USB controller to
the proper potential for MODE. When MUTE is high, the level at MODE should be 4.5-6.5 volts
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