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Circuit Descriptions, Abbreviation List, and IC Data Sheets

The supply unit delivers the following voltages to the chassis:

9.2.3

47" Sets

The 47" sets in this chassis come with a buy-in supply unit and
is a black-box for Service. When defective, a new panel must
be ordered and the defective panel must be sent for repair,
unless the main fuse of the panel is broken. Always replace a
defective fuse with one with the correct specifications! This part
is available in the regular market.
Refer to the Spare Parts list for the order number of the supply
unit.

9.3

On-Board Platform Supply

In this platform, an on-board platform supply has been
foreseen. This means that the mains voltage, after filtering, is
fed to the SSB.

The supply is a Self Oscillating Power Supply (SOPS) and
working according to the Quasi Resonant Conversion (QRC)
principle. For the on-board DC/DC converters refer to diagrams
B01A, B01B and B01C. For a complete description of the On-
Board Platform Supply, refer to the Q528.1E LA Service
Manual.

9.4

On-board DC/DC Converters

In this platform, on-board DC/DC converters have been
foreseen. See also diagrams B01A, B01B and B01C.

9.4.1

PSU Start-up Sequence

If the input voltage of the DC/DC converters is around 12 V
(measured on the decoupling capacitors 2U01/2U02) and
the ENABLE signals are “low” (active), then the output
voltages should have their normal values.

First, the Stand-by Processor activates the +1V2 supply
(via ENABLE-1V2).

Then, after this voltage becomes present and is detected
OK (about 100 ms), the other voltage of +3V3 will be
activated (via ENABLE-3V3).

The current consumption of controller IC 7U00 is around
20 mA (that means around 200 mV drop voltage across
resistor 3U01).

9.4.2

Internal Protection

•

Provides a SUPPLY-FAULT signal (active “low”), when the
output voltage of any DC/DC converter is out of its limits
(

10% of the normal value). In such cases, the Stand-by

Processor will immediately stop the supplies by sending a
“high” control signal towards the external and internal
supplies: ENABLE-xVx, POD-MODE, ON-MODE, and
STAND-BY.

Note:

The SUPPLY-FAULT control signal is “low” when

any DC/DC converter is disabled by its control signal
(ENABLE-xVx) and +12VSW is present, therefore it is
ignored during start-up!

•

The internal protection works together with the output over-
voltage detector transistors 7U07-1 and 7U07-2.

9.4.3

1.2V and 3.3V DC/DC Converters

Introduction

The circuit used is a so-called “synchronous buck converter”.
Some characteristics:
•

Switching frequency: approx. 250 kHz.

•

Efficiency: approx. 90%.

•

Built-in output over-voltage and over-current protections

•

Soft start.

•

Software controlled “on/off” (via ENABLE line).

Block diagram

Figure 9-4 Block diagram synchronous buck converter.

The advantage of a “synchronous buck converter” over a
“classical buck converter” is its better efficiency (about 90%).
The difference between the two is that in a synchronous buck
converter the “low -side” diode is replaced by a MOSFET TS2
(item 7U05). This, because the voltage drop across a MOSFET
is smaller than the forward voltage drop of a diode.
This second MOSFET TS2 conducts current during the “off”
times of the first MOSFET TS1 (item 7U08 at the input side).
The upper MOSFET TS1 conducts, to transfer energy from the
input to the inductor L

and load R

, while the lower MOSFET

TS2 conducts to circulate the inductor current (free wheel). The
synchronous PWM control block regulates the output voltage
by modulating the conduction intervals of the upper and lower
MOSFETs.

PWM Generator and MOSFET Drivers

This circuit is a one-chip solution (item 7U0A). It contains all the
circuitry for two independent buck regulators (3V3 and 1V2).
The MOSFETs 7U08, 7U02, 7U05 and 7U06 are the switching
transistors, they are conducting alternatively.
•

Time sequence 1: 7U08/7U02 is conducting; energy is
stored in coil 5U01/5U00. The current is flowing from the
+12VSW power supply source.

•

Time sequence 2: 7U08/7U02 is blocked; energy is stored
in coil 5U01/5U00.

•

Time sequence 3: 7U05/7U06 is conducting, and the
current circuit is now closed via 7U05/7U06, 5U01, 5U00,
2U06/2U0Z/2U07/2U0T/2U0U/2U0V, and the load. So the
energy stored in the coil during time sequence T1 is
consumed during sequence T3. The signal on the gate
7U05/7U06 is 180 degrees turned compared with the
signal on the gate 7U08/7U02.

Voltage Booster

This circuit is build around capacitors 2U29 and 2U26, resistor
3U62/3UA1, diodes 6U01 and 6U00, and transistor 7U03.
It generates the +18 V boost voltage on pin 4 of item 7U00, to
drive the “high-side” power MOS-FET 7U08/7U02. The voltage
is generated only during normal operation of the converter;
therefore, any drop in its value means an internal fault
condition, which is sensed by the internal protection circuit.
The AC component of the voltage on the source of transistor
7U08/7U02 is rectified by the diodes and added to the input
voltage, resulting into the boost voltage. The resistor
3U02/3U1K limits the peak current through the rectifier diodes.

Pin

1316

1319

1M09

1M90

1M95

1M99

HVR

HVL

+12V

+24V

+3V3standby