EN 1409.DVDR77/0xCircuit-, IC descriptions and list of abbreviations
The feedback control for the switched-mode power supply is reception, an additional circuit for suppressing the audio carrier
done by changing the conductive phase of the switching of the adjacent channel is used. This circuitry is adjusted by coil
transistor so that either more or less energy is transferred from [5710] for maximum suppression at 40.4MHz.
the rectified mains voltage at [2309] into the transformer. The
regulation information is provided by voltage reference [7315]. IF demodulator
This element compares the 5V-output voltage via voltage The signal from the tuner an-selection circuid IFt is processed
divider [3332, 3333, 3334] with an internal 2.5V reference by the demodulator IC TDA 9818/9817 [7710]. The signal
voltage. The output voltage of [7315] passes via an ?PSS? to pin 3 switches between demodulation of positive
optocoupler [7314] for intion of primarsula y and secondary (SECAM only) or negative modulated video carriers. A QSS-
parts as a current value into pin 3 on the IC [7313]. The switch-audio-IF signal SIF1 is generated for demodulation in the
on time of the transistois inversely proportionr [7307] al to the sound processor [7600]. The audio-IF carrier is selected in the
value of this current.audio SAW filter [1702]. er is swThis fiitched foltr SECAM L?. If
the signal ?SB1? is ?highhe switch?, t [7714] is closed and the
Overload, power limitation, burst mode:diode [6705] is not conducting.For all other stand ards the
With increasing load on one or more of the power supply diode [6705] is conducting and the switch [7714] is open. The
outputs, the switch-on time for the power transistor [7307] output signal of this SAW filter is firstly processed in the TDA
increases, and thus also tpeak value of the he delta-shaped 9818. Audio carriers are converted from the tuner IF level to the
current through this power transistor. The equivalent voltage of audio IF position and further processed in the audio
this current profile is passed from resistors [3321] and [demodulator [7600]. T3352] he AFC coil [5711] on the TDA 9818/
via [3365] to pin 5 of the IC [7313]. If the voltage on pin 2 9817 is adjusted so that when a frequency of 38.90 MHz is
reaches approx. 0.4V in one switching cycle, the conductive supplied to the IF output of the tuner, the AFC voltage on pin
phase of the switching traor is ennsistded immediately. The 17 of [7710] is 2.5V. The setting of the picture carrier frequency
check is done in each individuaswitching l cycle. This process for SECAM L in the TDA 9818 is achieved by connecting pin 7
ensures that no more than approx. 60W can be taken out from of the IC via a resistor [3710] to ground. The switch [7701] and
the mains ( = power limitation ).the signal ?SB1" do this. The HF-AGC is set using the
If the power supply reachepowes the r limit, the output voltages potentiometer [3724] so that, with a sufficiently large antenna
and the supply voltage Vcc on pin 1 of the IC [7313] will be input signal (74 dB?V), the voltage at the IF output of the tuner
reduced following further If Vcc is loading. less than approx. 9V [1705] pin 11 is 500 mVpp. This setting must be carried out
at any point during this process, the output of the IC [7313, pin when the audio carrier is switched off. The demodulated video
6] is blocked. All output voltages and Vcc decrease and a new signal appears on pin 16 of [7710]. The AGC voltage at pin 4 is
start-up cycle begins. If the overload status or short-circuit used to determine the antenna signal strength after a buffer
remains, the power limitation will be activated immediately and [7717] with the signal ?AGC? and an analog input port of the
the voltages will again decrease, followed by another start-up CC-P. The trap [1704] rehe sound carrier remainders induces t
cycle ( Burst Mode ). The amount of power taken up from the the video for BG standards. The trap [1706] works in the same
mains in burst mode is low.way for the Pal-I standard only. For all other standards the
switch [7713] is closed via [7706] and ?SFS_TS?-line set ?high"
Standby modes:to bypass this trap. In these cases the selectivity of the SAW
In the ?AV-Standby? operating mode of the set, the ?ION? control filter [1701] is sufficient. The coil [5713] for non-BG standards
line is primarily used to switch off all output voltages for Basic realizes a frequency respoectionse corrn. This correction is not
Engine and Digital Board (supplies 3V3, 5V, 12V, 5N and 4V6 desired for SECAM L' and the shoereforrt-circuited by [7716]
at Connectors 1932 and 1933) of the power supply. This (signal SB1 is ?high? and[7702] has on-statu s). The
reduces the amount of power taken from the mains. In Low demodulated video signal ?VFavailabV? is le after the buffer
Power Standby mode additionally the ?STBY? control line is and limiting stage for noise peaks [7711]. The FM-PLL
used to switch off output voltages 5SW and 8SW. This reduces demodulator function o9818f TDA is not necessary and
power consumption to less than 3W, if additionally the display therefore deactivated by the resistor [3739].
is switched off. The powy will continue operatiner supplg in
Standby mode with a switching frequency of approx. 25 kHz. Audio demodulator
The sound demodulation is done by the MSP3415 [7600],
2
9.3.3 Frontendwhich is also fully controlled via IC-bus by the CC-P
(determination of bandwidth, amplitude, standard, ...).The
audio signals are available at pin 30 and pin 31 of [7600] and
This unit is designed to support two basic versions, which are
fed as ?AFER?- & ?AFEL?-line to the audio-I/O for further
distinguished by a different assembly variant only (one for
processing.
multistandard and the second for Pal-I only) and comprises the
following parts:
Tuner UV1316K [1705]
IF amplifier & video demodulator IC TDA 9818/9817 [7710]
Sound processor MSP3415G [7600]
Tuner and IF selection
The Tuner [1705] converts the RF-signal coming from the
antenna input to an IF-signal. tuner is fully controThe lled via
2
IC-bus of the CC?P. [1705] is also- equipped with a ?passive-
loop-through? between antenna-in and -out to save power in
stand-by of the set, when the complete part is not supplied.
The IF frequency of the video carrier is 38.9 MHz for all
systems except SECAM L' (34,0 MHz).
A quasi-split audio system is used. Separate surface-wave
filters (SAW) are required. [1701], [1703] for video, [1702] for
audio. [1701] is switched into the signal path for DK/I-SECAM
L/L' reception, if the signal ?SFS_TS? is ?high?. In this case the
switches [7704], [7705] are open and the diode [6703] is
conducting. [1703] is swinto the signal itched path for BG
reception (?SFS_TS? is ?low?). Then the switch [7712] is open
and the diode [6704] is conducting. For DK/I-SECAM L/L' |
ACEC
