Circuit DescriptionL01.1E AB9.EN 69
A1
VIN
Degaussing
Control
Circuit
CINILLPCOUT
A1A2EHTB1/B2D
Mains ACMain SupplyFocusnAVOUT
InputMainVG2CRT
PowerVideoSupplyPanel
SupplyMain Aux
Filament
A15VD
Tilt&
Rotation
A1VGATECD
Degaussing
LotCircuit
3V3 Reg.VlotAux +13V
A2
EW
Correction
A2V
HorizontalVauxGATE
Deflection
+3.9V+3.3VA3
VlotAux -13VFrame
*VlotAux +50VDeflection
VT_SupplyA4nAVOUT
TunerVD
A7+3.3V
VlotAux +5VuPValley
+3.9V
VIN
A5
Video
Processing
0
A9MagnetizationDemagneti-
+8VSoundProcessingzationIL
A11
A8AudioVaux01234
Amplifier
t0t1 t2t3t00
+6.8VA10SourceT
SelectionCL 16532020_084.eps
Switch110401
CL 16532008_004.eps
250401
Figure 9-10
Figure 9-8
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
X e
-RQV Q
-
U
` Q
^
-`QR
gfirst interval, the MOSFET is switched ?on? and energy is
Uf
stored in the primary inductance (magnetisation). At the
bh7,8 ; %* +
"bhend, the MOSFET is switched ?off? and the second interval 7,-8 ; %%+
-&A<
bh7%-A &A Astarts.
b%"+
-%A<
Interval 2: t1 < t < t2 commutation time In the second
7%-%A
QQ7,8 ; %%&"+%- -*P<interval, the drain voltage will rise from almost zero to
i
- -!-&-& +
V% &+ -)-*P -)DB( IN+n(VOUT +VF). VF is the forward voltage drop of de
-)DB )-&A diode that will be omitted from the equations from now on.
-)DB(AQDBA
The current will change its positive derivative,
7,-8 ; %+
-%A &A A
%"+7%-%Acorresponding to VIN/LP, to a negative derivative,
CL 16532008_063.pdfcorresponding to -nVOUT /LP.
230501
Interval 3: t2 < t < t3 secondary stroke In the third interval,
the stored energy is transferred to the output, so the diode
Figure 9-9 starts to conduct and the inductive current IL will decrease.
In other words, the transformer will be demagnetised.
DegaussingWhen the inductive current has become zero the next
interval begins.
When the set is switched on, the degaussing relay 1515 is
Interval 4: t3 < t < t00 resonance time In the fourth interval,
immediately activated as transistor 7580 is conducting. Due to
the energy stored in the drain capacitor C will start to
the RC-time of R3580 and C2580, it will last about 3 to 4 D
resonate with the inductance L. The voltage and current
seconds before transistor 7580 is switched off.P
waveforms are sinusoidal waveforms. The drain voltage
will drop from VIN+nVOUT to VIN-nVOUT.
9.6.2 Basic IC Functionality
Frequency Behaviour
For a clear understanding of the Quasi-Resonant behaviour, it
The frequency in the QR-mode is determined by the power
is possible to explain it by a simplified circuit diagram (see
stage and is not influenced by the controller (important
Figure below). In this circuit diagram, the secondary side is
parameters are LP and CD). The frequency varies with the input
transferred to the primary side and the transformer is replaced
voltage VIN and the output power POUT. If the required output
by an inductance LP. CD is the total drain capacitance including
power increases, more energy has to be stored in the
the resonance capacitor CR, parasitic output capacitor COSS of
transformer. This leads to longer magnetising tPRIM and
the MOSFET and the winding capacitance CW of the
demagnetising tSEC times, which will decrease the frequency.
transformer. The turns ratio of the transformer is represented
See the frequency versus output power characteristics below.
by n (NP/NS).
The frequency characteristic is not only output power-, but also
input voltage dependent. The higher the input voltage, the
smaller tPRIM, so the higher the frequency will be. |
ACEC
