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Derived Voltages
The voltages supplied by the secondary windings of T5520 are:
•
'MainAux' for the audio circuit (voltage depends on set
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.
A1
Degaussing
Control
Circuit
A1
Mains AC
Input
Main
Power
Supply
+3.9V
Figure 9-8 Derived voltages
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 LP. CD is the total drain capacitance including the
resonance capacitor CR, parasitic output capacitor COSS of
the MOSFET and the winding capacitance CW of the
transformer. The turn ratio of the transformer is represented by
n (NP/NS).
EHT
A2
Main Supply
Focus
VG2
VideoSupply
Main Aux
Filament
Lot
VlotAux +13V
3V3 Reg.
+3.3V
VlotAux -13V
*VlotAux +50V
VT_Supply
VlotAux +5V
+8V
+6.8V
Published in Heiloo Holland
Circuit Description
B1/B2
CRT
Panel
A15
Tilt&
Rotation
A1
Degaussing
Circuit
A2
EW
Correction
A2
Horizontal
Vaux
Deflection
A3
Frame
Deflection
A4
Tuner
A7
+3.3V
uP
+3.9V
A5
Video
Processing
A9
Sound
Processing
A11
A8
Audio
Vaux
Amplifier
A10
Source
Selection
Switch
CL 16532008_004.eps
250401
L01.1U AC
V
IN
C
I
L
IN
L
P
D
V
GATE
V
GATE
V
D
V
IN
0
Magnetization
Demagneti-
zation
I
L
2
1
0
t
t
t
0
1
2
T
Figure 9-9 QR-mode time intervals
In the Quasi-Resonant mode each period can be divided into
four different time intervals, in chronological order:
•
Interval 1: t0 < t < t1 primary stroke. At the beginning of
the first interval, the MOSFET is switched 'on' and energy
is stored in the primary inductance (magnetization). At the
end, the MOSFET is switched 'off' and the second interval
starts.
•
Interval 2: t1 < t < t2 commutation time. In the second
interval, the drain voltage will rise from almost zero to
V
+n•(V
+V
). V
is the forward voltage drop of de
IN
OUT
F
F
diode that will be omitted from the equations from now on.
The current will change its positive derivative,
corresponding to V
/L
, to a negative derivative,
IN
P
corresponding to -n•V
/LP.
OUT
•
Interval 3: t2 < t < t3 secondary stroke. In the third
interval, the stored energy is transferred to the output, so
the diode starts to conduct and the inductive current I
decrease. In other words, the transformer will be
demagnetized. When the inductive current has become
zero the next interval begins.
•
Interval 4: t3 < t < t00 resonance time. In the fourth
interval, the energy stored in the drain capacitor C
start to resonate with the inductance L
current waveforms are sinusoidal waveforms. The drain
voltage will drop from V
+n•V
IN
Frequency Behavior
The frequency in the QR-mode is determined by the power
stage and is not influenced by the controller (important
parameters are L
and C
). The frequency varies with the input
P
D
voltage V
and the output power P
IN
power increases, more energy has to be stored in the
transformer. This leads to longer magnetizing t
demagnetizing t
times, which will decrease the frequency.
SEC
See the frequency versus output power characteristics below.
The frequency characteristic is not only output power-, but also
input voltage dependent. The higher the input voltage, the
smaller t
, so the higher the frequency will be.
PRIM
22/11/2016
9.
EN 99
C
OUT
n⋅V
OUT
V
D
C
D
n⋅V
OUT
Valley
3
4
t
t
3
00
CL 16532020_084.eps
110401
will
L
will
D
. The voltage and
P
to V
-n•V
.
OUT
IN
OUT
. If the required output
OUT
and
PRIM
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