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EN 104
9.
SACD 900
Start-up and Take-over Circuitry
With the mains voltage input, C7 will charge. When this
voltage, (at pin 7 of IC1), reaches the start-up threshold of min
14.5 V, the control circuit starts to operate.
After start-up, IC1 requires a maximum sinking current of 17
mA, which the start-up circuitry cannot deliver. Therefore, a
take-over circuitry (a coupled winding of transformer T1) is
present. The voltage at this point will take over the supply
voltage at pin 7 of the IC.
If the take-over circuit does not function, the IC will switch 'off'
again at the minimal operating voltage of 8.5 V. The whole
operation cycle will repeat itself with audible hiccup sound if
take-over is not present.
Secondary Voltage Sensing
The secondary voltage regulating circuit comprises of opto-
coupler IC2 (which isolates the error signal from the control IC
on the primary side), and a reference component IC3 (TL431).
The reference component has two functions:
•
a very stable and accurate reference diode
•
a high gain amplifier.
TL431
R
2.5V
CL 96532065 071 eps
Figure 9-2
When the output voltage increases (due to a reduction in the
load), the voltage across R23 increases to above the internal
reference voltage of 2.5 V. IC3 will conduct and the current
through the opto-coupler will increase. This results in an
increase of the voltage at pin 2 of IC1, which will reduce the on
time of FET Q1.
In the event of an output voltage decrease (due to an increase
in the load), the control circuit will operate in the opposite way.
Primary Current Sensing
The current through FET Q1, will result in a voltage drop across
R3A. This line goes to pin 3 of IC1, which is the current sense
input. The higher the input voltage, the more the primary
current is limited. In this way, the maximum output power of the
power supply is limited.
Under-voltage Protection
Two under-voltage lockout comparators are incorporated, to
guarantee that IC1 is fully functional
before the output stage is enabled. Separate comparators with
built-in hysteresis monitor both the supply voltage at pin 7 and
the reference voltage at pin 8.
If the supply voltage at pin 7 drops below 10 V (typical), e.g.
due to a shorted secondary voltage or
excessive load, the drive pulse at pin 6 is disabled and the
controller will switch 'off'.
Over-voltage Protection
The over-voltage circuitry (ZD1, Q7, and Q8) is used to detect
an over-voltage situation on the secondary side of the
transformer.
If, after start-up, the voltage at the zenerdiode ZD1 will exceeds
its zener voltage, the internal latch circuit is triggered (via pin
1), the output buffer is disabled, and the SMPS goes into over-
voltage protection. Now a complete restart sequence is
required.
Note: If the event of the over-voltage situation remains present,
the SMPS will go in sequence of protection, start-up, protection
and the cycle repeats. This effect is highly audible.
Circuit Descriptions and List of Abbreviations
K
A
130799
9.3
Loader/Monoboard
SD1.1 Loader Assy
SERVO PART
LOADER
7207
TRAY
7102
MACE 2
SERVO uP
OPU
SERVO
HF
7311
SRAM
SAA7335
DECODER
2
I
S
DIGITAL PART
7401
7503
FLASH
ROM
7504/05
STi 5508/5580
SDRAM
HOST uP
7505
NVM
2
C
SERVICE
I
INTERFACE
Figure 9-3
9.3.1
The Servo Part
The Optical Unit
The optical unit consists of two lasers, one for CD with a
wavelength of 780 nm, and one for DVD with a wavelength of
650 nm. The TZA1033 (item 7102) controls the data from these
lasers, and the supply to them.
The Signal Processor TZA1033
The TZA1033 (or DVDALAS2) is an analogue pre-processor
and laser supply circuit. It contains data amplifiers and several
options for radial tracking and focus control.
It is possible to optimise the dynamic range of this pre-amp/
processor combination for the LF servo and RF data paths. The
gain in both channels is separately programmable. This will
guarantee an optimal playability for all kind of discs.
Also, a dual laser supply is implemented, with fully automatic
laser control including stabilisation and an ON/OFF switch, plus
a separate supply pin for power efficiency.
The servo signals go to the MACE2 servo processor, while the
HF output signal, goes to the SAA7335 decoder (item 7311).
The Servo Processor MACE2
The servo circuit in the MACE2 IC (item 7207), takes care of
the servo controls. In a CD system, there are some 12 control
loops active. About six of them are needed to adjust the servo
error signals, that is once per disc rotation. It also adjusts
offsets, signal amplitudes, and loop gains (AGCs), to enlarge
system robustness and to avoid expensive potentiometer
adjustments in production.
The other six loops determine the laser spot position on the
disc in the radial, axial (focus), and tangential directions.
It also has to take care that the spot accesses a required
position as fast as possible. This access system consists of two
parts, namely the actuator and the sled, which are (within a
certain range) mechanically and electrically independent.
Therefore, during an access, the servo has to control as well
the actuator as the sled.
The analogue signals from the diode pre-processor are
converted into a digital representation using A/D converters.
For the communication between the host processor (STi5505)
and the servo processor the S2B bus is used, this supports full-
duplex asynchronous communication.
Note: For an extensive description of the MACE2 IC, see
Service Manual 3122 785 11010.
The Decoder SAA7335
The SAA7335 (item 7311) is a high-end combined Compact
Disc (CD) and Digital Versatile Disc (DVD) compatible
decoding device. The device operates with an external 32 KB
SRAM for DVD error correction and de-interleaving operations.
7202
[FROM AV BOARD]
FLASH
384 * fs
7401/51
7700
7905
FLASH
PLL
SDRAM
ROM
S2B
27MHz
7800
27MHz
EMI
HF
FURORE
2
DSD DECODER
I
S
SPD F / PCM
VIDEO
F LTER
CL16532136 045 eps
261101
AUDIO
(DSD / PCM)
AUDIO
(PCM / IEC 958)
VIDEO
(RGB / YC /CVBS)
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