Philips L01.1L AC Service Manual Download

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Circuit Description

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

Figure 9-4 Switched Mode Power Supply standard circuit

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

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
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 9-6 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 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).

Demag

Ctrl

Gnd

Vcc

Drain

HVS

Driver

Sense

LINE

TEA1507

SENSE

OUT