Table of Contents
Advertisement
A1
Degaussing
Control
Circuit
A1
Main Supply
Mains AC
Input
Main
Power
Supply
Main Aux
3V3 Reg.
+3.9V
+3.3V
Figure 9-8
3RZHU VXSSO\ YROWDJHV /
6FUHHQ
9ROWDJH
0HDV
6L]H
QDPH
SRLQW
´
0DLQ6XSSO\
3 &
´
0DLQ$X[
3 &
´
´
$OO
0DLQ6XSSO\
3 &
RWKHUV
0DLQ$X[
3 &
Figure 9-9
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 behaviour,
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
capacitance including the resonance capacitor C
output capacitor C
of the MOSFET and the winding
OSS
capacitance C
of the transformer. The turns ratio of the
W
transformer is represented by n (N
EHT
A2
B1/B2
Focus
VG2
CRT
Panel
VideoSupply
Filament
A15
Tilt&
Rotation
A1
Degaussing
Circuit
Lot
VlotAux +13V
A2
EW
Correction
A2
Horizontal
Vaux
Deflection
A3
VlotAux -13V
Frame
Deflection
*VlotAux +50V
VT_Supply
A4
Tuner
A7
+3.3V
VlotAux +5V
uP
+3.9V
A5
Video
Processing
A9
Sound
+8V
Processing
A11
A8
Audio
Vaux
Amplifier
A10
+6.8V
Source
Selection
Switch
CL 16532008_004.eps
250401
9DOXH
5HPDUN
9
9
6WHUHR [ : DQG
0RQR [ : : :
9
6WHUHR [ : DQG
0RQR [ :
9
5) DQG
9
9
6) %/'
%/6 :6
%/':6
%/6:6
9
6WHUHR [ : : :
9
0RQR [ :
CL 16532008_063.pdf
230501
. C
is the total drain
P
D
, parasitic
R
/N
).
P
S
Circuit Description
V
IN
C
IN
V
GATE
V
GATE
V
D
0
Magnetization
I
L
0
t
0
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
(magnetisation). 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
IN
OUT
diode that will be omitted from the equations from now
on. The current will change its positive derivative,
corresponding to V
corresponding to -n•V
•
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
demagnetised. 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
Frequency Behaviour
The frequency in the QR-mode is determined by the power
stage and is not influenced by the controller (important
parameters are L
input voltage V
output power increases, more energy has to be stored in the
transformer. This leads to longer magnetising t
demagnetising t
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
L01.1A
9.
I
L
L
P
C
OUT
D
n⋅V
OUT
V
D
C
D
n⋅V
OUT
Valley
V
IN
Demagneti-
zation
1
2
3
4
t
t
t
t
1
2
3
00
T
CL 16532020_084.eps
110401
Figure 9-10
+V
). V
is the forward voltage drop of de
F
F
/L
, to a negative derivative,
IN
P
/L
.
OUT
P
. The voltage and
P
+n•V
to V
-n•V
IN
OUT
IN
and C
). The frequency varies with the
P
D
and the output power P
. If the required
IN
OUT
times, which will decrease the frequency.
SEC
, so the higher the frequency will be.
PRIM
GB 79
will
L
will
D
.
OUT
and
PRIM
Hide quick links:
Advertisement
Table of Contents
