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Circuit Description

Over Current Protection
The internal OCP protection circuit limits the 'sense' voltage on
pin 5 to an internal level.

Over Power Protection
During the primary stroke, the rectified AC input voltage is
measured by sensing the current drawn from pin 4 (DEM). This
current is dependent on the voltage on pin 9 of transformer
5520 and the value of R3522. The current information is used
to adjust the peak drain current, which is measured via pin
I

SENSE

Short Winding Protection
If the 'sense' voltage on pin 5 exceeds the short winding
protection voltage (0.75 V), the converter will stop switching.
Once V

drops below the UVLO level, capacitor C2521 will be

recharged and the supply will start again. This cycle will be
repeated until the short circuit is removed (safe restart mode).
The short winding protection will also protect in case of a
secondary diode short circuit.
This protection circuit is activated after the leading edge
blanking time (LEB).

LEB time
The LEB (Leading Edge Blanking) time is an internally fixed
delay, preventing false triggering of the comparator due to
current spikes. This delay determines the minimum 'on' time of
the controller.

Over Temperature protection
When the junction temperature exceeds the thermal shutdown
temperature (typ. 140º C), the IC will disable the driver. When
the V

voltage drops to UVLO, the V

capacitor will be

recharged to the V(start) level. If the temperature is still too
high, the V

voltage will drop again to the UVLO level (Safe-

Restart mode). This mode will persist until the junction
temperature drops 8 degrees typically below the shutdown
temperature.

Mains dependent operation enabling level
To prevent the supply from starting at a low input voltage, which
could cause audible noise, a mains detection is implemented
(Mlevel). This detection is provided via pin 8, which detects the
minimum start-up voltage between 60 and 100 V. As previous
mentioned, the controller is enabled between 60 and 100 V.
An additional advantage of this function is the protection
against a disconnected buffer capacitor (C

). In this case, the

supply will not be able to start-up because the V

capacitor

will not be charged to the start-up voltage.

9.7

Control

Figure 9-16 Block diagram set control

9.7.1

Introduction

The microprocessor part of the UOC, has the complete control
and teletext on board. User menu, Service Default Mode,
Service Alignment Mode and Customer Service Mode are
generated by the uP. Communication to other ICs is done via
the I

C-bus.

9.7.2

C-Bus

The main control system, which consists of the microprocessor
part of the UOC (7200), is linked to the external devices (tuner,
NVM, MSP, etc) by means of the I

C-bus. An internal I

C-bus

is used to control other signal processing functions, like video
processing, sound IF, vision IF, synchronization, etc.

9.7.3

User Interface

The 'L01.1U AC' uses a remote control with RC5 protocol. The
incoming signal is connected to pin 67 of the UOC.

The 'Top Control' keyboard, connected to UOC pin 80, can also
control the set. Button recognition is done via a voltage divider.

The front LED (6691) is connected to an output control line of
the microprocessor (pin 5). It is activated to provide the user
information about whether or not the set is working correctly
(e.g., responding to the remote control, normal operation (USA
only) or fault condition)

9.7.4

In- and Output Selection

For the control of the input and output selections, there are
three lines:
•

STATUS1. This signal provides information to the
microprocessor on whether a video signal is available on
the SCART1 AV input and output port (only for Europe).
This signal is not connected in NAFTA sets.

•

STATUS2. This signal provides information to the
microprocessor on whether a video signal is available on
the SCART2 AV input and output port (only for Europe).
For sets with an SVHS input it provides the additional

CL 16532016_015.eps

220301

Signal

Processing

User

Interface

uP - Control

LED

PANORAMA

BUZZ

BASS

TREBLE/Tilt