Panasonic EURO 4 Chassis Technical Manual page 82

3DQDVRQLF
25.2. Secondary Side
25.2.1.Audio Power Supply
This supply is used to fed the rear / centre and
Super 3D Bass channel to amplifier ICs,
IC2703 and IC2704. The pulses from pin 6 winding
S2 of T2701 are rectified by diode D2710 and
applied to the emitters of transistors
resistor R2714 to Q2702. At the same time pulses
from pin 7 winding S7 of T2701 are rectified by diode
D2711,applying a supply voltage of 18V to pins 5 of
IC2702 / IC2703 and IC2704.
The audio amplifiers TDA2030 work on a split
supply. The -18V supply is fed from pin 8, winding
S1 of T2701 and fed to pin 3 of the above mentioned
amplifiers.
This split supply gives TDA2030 a supply voltage of
36V. However as this supply voltage is too large for
the amplifiers TDA2030 when under load, the supply
voltage has to be reduced, this is achieved by
reducing the +18V supply rail thus reducing the
overall supply voltage of TDA2030.
IC2702 /
As the load on TDA2030 increases the voltage drop
across R2715 increases causing the base of
to become more negative with respect to its emitter.
Q2701 and via
With
becomes more positive with respect to its emitter,
thus causing the supply voltage to TDA2030 to be
reduced.
However by reducing the supply voltage to TDA2030
the output power of TDA2030 is also reduced. This
is compensated for by the increased voltage drop
across resistors R2712 / R2713 causing an
increased current flow. This inturn ensures that the
output power of TDA2030 is not affected.
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Q2701 conducting the base bias of
Q2701
Q2702