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Service Manual CP-099F
5-7 Sound amplification
The TDA8944J (TDA8946J) is a stereo BTL audio amplifier capable of delivering 2 x 5W output power to
an 8 W load at THD = 10%, using a 12 V power supply and an external heatsink. The voltage gain is fixed at 32dB.
With the three-level MODE input the device can be switched from ‘standby’ to ‘mute’ and to ‘operating’ mode.
The TDA 8944J outputs are protected by an internal thermal shutdown protection mechanism and short-circuit
protection.
5-7-1 Power amplifier
The power amplifier is a Bridge Tied Load (BTL) amplifier with an all-NPN output stage, capable of delivering a peak
output current of 1.5 A.
The BTL principle offers the following advantages :
- Lower peak value of the supply current.
- The ripple frequency on the supply voltage is twice the signal frequency.
- No DC-blocking capacitor
- Good low frequency performance
In the case of 2 Carrier FM transmission, the controlling software read the transmission mode and the signal quality level
from the Stereo Detection Register. When the set is in “Auto detection” mode the controlling software automatically sets
the sound mode ( mono, Stereo, Dual 1, Dual 2 ) depending on the transmitted mode.
In “Auto detection” mode the controlling software evaluates the signal quality and automatically switches to the analogue
sound carrier 1, if the transmission quality is too poor. To avoid unwanted automatic switching the threshold levels
mono to stereo and stereo to mono are different.
In “forced mono “ mode ( Red OSD in status Display Window), the controlling software configures the MSP341xD to
demodulate the analogue (FM or AM) sound carrier 1, no matter the signal quality. The sound mode “ forced “ or “
Autodetect” is stored for each programme.
5-7-2 Mode selection
The TDA894xJ has several functional modes, which can be selected by applying the proper DC voltage to pin MODE.
Mute : In this mode the amplifier is DC biased but not operational (no audio output). This allows the input coupling
capacitors to be charged to avoid pop-noise. The device is in mute mode when 2.5 V < V
MODE
< (Vcc-1.5 V).
Operating : In this mode the amplifier is operating normally. The operating mode is activated at V
MODE
< 0.5 V.
5-8 Vertical deflection
The vertical driver circuit is a bridge configuration. The deflection coil is connected between the output amplifiers,
which are driven in phase opposition. The differential input circuit is voltage driven. The input circuit is especially
intended for direct connection to driver circuits which deliver symmetrical current signals, but is also suitable for
asymmetrical currents. The output current of these devices is converted to voltages at the input pins via resistors R303
and R304. The differential input voltage is compared with the output current through the deflection coils measured as
voltage across R311, which provides internal feedback information. The voltage across R311 is proportional to the
output current.
5-8-1 Flyback voltage
The flyback voltage is determined by an additional supply voltage V
flb
. The principle of operation with two supply
voltages (class G) makes it possible to fix the supply voltage Vp optimum for the scan voltage and the second supply
voltage V
flb
optimum for the flyback voltage. Using this method, very high efficiency is achieved. The supply voltage
V
flb
is almost totally available as flyback voltage across the coil, this being possible due to the absence of a coupling
capacitor.
5-8-2 Protection
The output circuit has protection circuits for :
- Too high die temperature
- overvoltage of output stage A
Summary of Contents for DDT-21H9ZZF
Page 17: ...16 Service Manual CP 099F...
Page 36: ...Service Manual CP 099F 35 5 Circuit desription 5 1 Block diagram...
Page 60: ...Service Manual CP 099F 59 5 11 3 SCHEMATIC DIAGRAM 5 11 3 1 AUDIO...
Page 61: ...Service Manual CP 099F 60 5 11 3 2 DRIVE RF...
Page 62: ...Service Manual CP 099F 61 5 11 3 3 DSP...
Page 63: ...Service Manual CP 099F 62 5 11 3 4 MICOM...
Page 64: ...Service Manual CP 099F 63 5 11 3 5 MPEG...
Page 77: ...Service Manual CP 099F 76 9 PRINTED CIRCUIT BOARD 9 1 DVD PCB The upper...
Page 78: ...Service Manual CP 099F 9 2 DVD PCB The lower 77...
Page 79: ...Service Manual CP 099F 9 3 POWER PCB 78...
Page 80: ...Service Manual CP 099F 9 4 MAIN PCB 79...
Page 81: ...80 Service Manual CP 099F 10 SCHEMATIC DIAGRAM 10 1 POWER CRT...
Page 82: ...81 Service Manual CP 099F 10 SCHEMATIC DIAGRAM 10 2 PCB MAIN...