Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 125
Q528.1E LA
9.
The output voltages of +12 V, +15 V, and +24 V (or +295 V in
case of scanning backlight) are generated through a so-called
resonant DC-DC power converter (LLC-converter) (item no.
7005 to 7008 in diagram A2).
An over-voltage protection circuitry is built around item no.
6020 and 6009 and will activate if the feedback circuitry is
defective (see diagram A2).
A primary over-current protection circuitry is built around item
no. 3055 and 2047 and will activate in case the MOSFETS
(item no. 7005 and 7006) are short-circuited. A secondary
over-current protection circuitry is built around item no. 2014
and 3021 and will activate a soft-start if a short-circuit is
detected in the 12 V and 24 V secondary circuits. See diagram
A2 for details.
The following signals interface with the SSB via connector
1P11 (see diagram A1):
•
DIM-control: adjusts backlight intensity (pulse-width
modulated signal of 3.3 V).
•
Power-Good.
•
Light on_off: switches the LCD backlight (0 - 3.3 V).
•
Boost (fixed: ór 3.3 V ór left “open” depending on
commercial request or display specification).
•
Stand-by: stand-by signal and 5.2 V from SSB to switch
relay on Display Supply Unit on/off.
9.2.2
47”
S
ets
The 47” sets in this chassis come with a buy-in Sanken Display
Supply unit and is a black-box for Service. When defective, a
new panel must be ordered and the defective panel must be
sent for repair, unless the main fuse of the panel is broken.
Always replace a defective fuse with one with the correct
specifications! This part is available in the regular market.
The supply unit works together with the on-board platform
supply (see section “On-Board Platform Supply”).
Two versions of this supply unit can be used in this platform:
•
Output voltage of +295 V for the scanning backlight
displays (not in US region)
•
Output voltage of +24 V for all other displays.
Always refer to the Spare Parts list for the correct order
number!
The supply unit delivers the following voltages to the chassis:
•
Mains voltage (filtered) for SSB (connector 1P02)
•
+395 V DC (connector 1P22)
•
Scanning backlight display: +295 V DC (connectors 1P05/
1P06)
Non scanning backlight display: +24 V DC (connectors
1319/1316)
•
+12 V DC on connectors 1M09, 1M12 and 1P15.
When all these voltages are present, the Power-Good signal
becomes “high” (+5 V) (connectors 1P10.2 and 1P11.2).
9.3
On-Board Platform
S
upply
In this platform, an on-board platform supply has been
foreseen. This means that the mains voltage, after filtering, is
fed to the SSB.
The supply is a Self Oscillating Power Supply (SOPS) and
working according to the Quasi Resonant Conversion (QRC)
principle. Refer to diagrams B01A and B01B for details. For the
on-board DC/DC converters refer to diagrams B02A, B02B and
B02C.
9.3.1
S
tart-up sequence
When the Platform Supply is switched “on”, the voltage across
capacitor 2B50 increases. This will trigger the gate of MOSFET
7B05 (via resistors 3B60 and 3B34). When the voltage on pin
1 of the MOSFET reaches the threshold level, the MOSFET
starts conducting. As result, current will flow in the primary
winding of transformer 5B01. The output voltage increases but
the supply will not start oscillating because the auxiliary voltage
is still too “low” to drive the MOSFET autonomously. Oscillating
will start only when then auxiliary voltage across capacitor
2B32 is high enough to drive the gate of the MOSFET. This
brings the supply in SOPS mode (self-oscillating).
9.3.2
Reduced / Maximum Power Mode
When there is no overload and when the supply has reached
SOPS mode, the start-up power consumption is limited to appr.
1 A in order to ensure a slow start current control across the
MOSFET. This will last as long as diode 6B14 is not (yet)
conducting while transistor 7B01 is conducting, thus keeping
the supply in Reduced Power Mode.
In general, the “on” time of the transistor 7B05 is a function of
the output current. Resistor 3B51 can be seen as sense
resistor with a voltage of V
drop
. If there is a demand for more
power, the negative voltage created from the auxiliary winding
and diode 6B11 will cause diode 6B14 and transistor 7B01 to
conduct. Transistor 7B01 will put resistor 3B49 in parallel to
resistors 3B50 and 3B51. This will result in V
drop
across resistor
3B51 to be lower, which causes the “on” time of transistor 7B05
to be longer, which enables the supply to deliver more power.
This brings the supply in Maximum Power Mode.
9.3.3
Peak current control
The peak start-up current flowing across the MOSFET also
influences the voltage across the sense resistor 3B51 and will
cause transistors 7B02 and 7B00 to conduct (via resistor
3B50). The voltage across this resistor is sensed in order to
control the maximum power.
9.3.4
Output voltage control
The voltage at the +12 V output supply line will increase until
the zener voltage of diodes 6B02 and 6B13 is reached. The
output voltage is controlled via a feedback-loop formed by
components 3B54, 6B02, 6B13, 7B04, 3B47, 7B02 and 7B00.
When the voltage exceeds 12.6 V the zener diodes 6B02 and
6B13 will conduct and will trigger opto-coupler 7B04. After a
while transistors 7B02 and 7B00 will start to conduct and this
will switch “off” MOSFET 7B05. The feedback-loop will become
stable after a while, thus controlling the output voltage.
9.3.5
Over-voltage protection
In case of malfunctioning of the output voltage control
feedback-loop as described above, the supply goes into over-
voltage protection. When the negative primary auxiliary voltage
(present at the anode of diode 6B11) reaches the zener voltage
of diode 6B03, MOSFET 7B05 will switch off. This causes
transistors 7B02 and 7B00 to conduct which will result in an
output voltage drop.
9.3.6
Audio protection / DC protection
When a fault occurs in the audio amplifiers (e.g.a short-circuit),
a voltage is sent via the AUDIO-PROT line which will trigger
thyristor 7B50. This will cause the +12 V output line to drop to
appr. +3 V. The only way to reset the thyristor is to disconnect
the set from mains. After re-connect to mains, the supply will
restart normally, if the defective audio amplifier has been
repaired.
