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frequency of the line deflection coil and the S-correction
capacitors and therefore a less steep S-corrected line
deflection current.
9.6
Power Supply
V
LINE
V
CC
TEA1507
1
Vcc
2
Gnd
3
Ctrl
Driver
4
Demag
Figure 9-4 Switched Mode Power Supply standard circuit
1
SUPPLY
V CC
MANAGEMENT
internal
UVLO start
supply
M-level
S1
2
VOLTAGE
GND
CONTROLLED
OSCILLATOR
FREQUENCY
CONTROL
OVER-
TEMPERATURE
PROTECTION
3
−1
CTRL
POWER-ON
RESET
UVLO
2.5 V
burst
detect
MAXIMUM
ON-TIME
PROTECTION
TEA1507
Figure 9-5 Internal block diagram of the driver IC (TEA1507)
9.6.1
Introduction
The supply is a Switching Mode Power Supply (SMPS). The
frequency of operation varies with the circuit load. This 'Quasi-
Resonant Flyback' behavior has some important benefits
compared to a 'hard switching' fixed frequency Flyback
converter. The efficiency can be improved up to 90%, which
results in lower power consumption. Moreover, the supply runs
cooler and safety is enhanced.
The power supply starts operating when a DC voltage goes
from the rectifier bridge via T5520, R3532 to pin 8. The
operating voltage for the driver circuit is also taken from the
'hot' side of this transformer.
The switching regulator IC 7520 starts switching the FET 'on'
and 'off', to control the current flow through the primary winding
of transformer 5520. The energy stored in the primary winding
during the 'on' time is delivered to the secondary windings
during the 'off' time.
The 'MainSupply' line is the reference voltage for the power
supply. It is sampled by resistors 3543 and 3544 and fed to the
V
IN
C
IN
N
P
N
S
Drain
8
C
D
HVS
7
6
C
SS
Sense
5
R
SS
R
SENSE
N
Vcc
CL 16532020_074.eps
START-UP
CURRENT SOURCE
clamp
VALLEY
LOGIC
100 mV
OVER-
VOLTAGE
PROTECTION
LOGIC
DRIVER
I ss
LEB
S
Q
soft
start
blank
S2
R
Q
OCP
short
0.75 V
winding
OVERPOWER
PROTECTION
CL 16532020_073.eps
Circuit Description
input of the regulator 7540 / 6540. This regulator drives the
feedback optocoupler 7515 to set the feedback control voltage
on pin 3 of 7520.
The power supply in the set is 'on' any time AC power goes to
the set.
Derived Voltages
The voltages supplied by the secondary windings of T5520 are:
•
'MainAux' for the audio circuit (voltage depends on set
V
OUT
execution, see table below),
•
3.3 V and 3.9 V for the microprocessor and
•
'MainSupply' for the horizontal output (voltage depends on
set execution, see table below).
Other supply voltages are provided by the LOT. It supplies +50
V (only for large screen sets), +13 V, +8 V, +5 V, and a +200 V
source for the video drive. The secondary voltages of the LOT
are monitored by the 'EHTinformation' lines. These lines are
fed to the video processor part of the UOC IC 7200 on pins 11
and 34.
This circuit will shut 'off' the horizontal drive in case of over-
voltage or excessive beam current.
Mains AC
Input
120401
8
DRAIN
7
HVS
n.c.
4
DEM
6
DRIVER
0.5 V
5
I sense
060701
Degaussing
When the set is switched on, the degaussing relay 1515 is
immediately activated as transistor 7580 is conducting. Due to
the RC-time of R3580 and C2580, it will last about 3 to 4
seconds before transistor 7580 is switched off.
9.6.2
Basic IC Functionality
For a clear understanding of the Quasi-Resonant behavior, it is
possible to explain it by a simplified circuit diagram (see Figure
below). In this circuit diagram, the secondary side is transferred
to the primary side and the transformer is replaced by an
inductance L_p. Capacitor C_d is the total drain capacitance
including the resonance capacitor C_r, parasitic output
capacitor C_oss of the MOSFET and the winding capacitance
C_w of the transformer. The turn ratio of the transformer is
represented by n (N_p/N_s).
L01.1L AC
A1
Degaussing
Control
Circuit
EHT
A1
A2
Main Supply
Focus
Main
VG2
Power
VideoSupply
Supply
Main Aux
Filament
Lot
VlotAux +13V
3V3 Reg.
+3.9V
+3.3V
VlotAux -13V
*VlotAux +50V
VlotAux +5V
+8V
Figure 9-6 Derived voltages
9.
EN 75
B1/B2
CRT
Panel
A15
Tilt&
Rotation
A1
Degaussing
Circuit
A2
EW
Correction
A2
Horizontal
Vaux
Deflection
A3
Frame
Deflection
VT_Supply
A4
Tuner
A7
+3.3V
uP
+3.9V
A5
Video
Processing
A9
Sound
Processing
A11
A8
Audio
Vaux
Amplifier
A10
Source
+6.8V
Selection
Switch
CL 16532008_004.eps
250401
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