Philips L01.1U Service Manual Download Page 99

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Circuit Description

EN 99

L01.1U AC

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 su50
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.

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).

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

OUT

). V

is the forward voltage drop of de

diode that will be omitted from the equations from now on.
The current will change its positive derivative,
corresponding to V

, to a negative derivative,

corresponding to -n•V

OUT

/LP.

•

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

will

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

will

start to resonate with the inductance L

. The voltage and

current waveforms are sinusoidal waveforms. The drain
voltage will drop from V

+n•V

OUT

to V

-n•V

OUT

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

voltage V

and the output power P

OUT

. If the required output

power increases, more energy has to be stored in the
transformer. This leads to longer magnetizing t

PRIM

and

demagnetizing t

SEC

times, which will decrease the frequency.

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

PRIM

, so the higher the frequency will be.

CL 16532008_004.eps

250401

Tilt&
Rotation

A15

Lot

EHT

VG2

VideoSupply

Filament

Focus