Vtun Generator; 8V6 Switch; Useful Data; Pwm Generator And Mosfet Drivers - Philips 42PF9731D Service Manual

Circuit Descriptions, Abbreviation List, and IC Data Sheets
The upper MOSFET TS1 conducts, to transfer energy from the
input to the inductor L
1
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 7U00). It contains all the
circuitry for two independent buck regulators (3V3 and 1V2).
The MOSFETs T7U01 and T7U03 are the switching
transistors, they are conducting alternatively.
• Time sequence 1: T7U01 is conducting; energy is stored in
coil 5U00/5U03. The current is flowing from the +12VSW
power supply source.
• Time sequence 2: T7U01 is blocked; energy is stored in
coil 5U00/5U03.
• Time sequence 3: T7U03 is conducting, and the current
circuit is now closed via T7U03, Coil 5U00/5U03, C2U24/
2U22, and the load. So the energy stored in the coil during
time sequence T1 is consumed during sequence T3. The
signal on the gate T7U03 is 180 degrees turned compared
with the signal on the gate T7U01.
Voltage Booster
This circuit is build around capacitors 2U11 and 2U26, resistor
3U11, diodes 6U22 and 6U23, and transistor 7U07.
It generates the +18 V boost voltage on pin 4 of item 7U00, to
drive the "high-side" power MOS-FET 7U01. 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
7U01 is rectified by the diodes and added to the input voltage,
resulting into the boost voltage. The resistor 3U11 limits the
peak current through the rectifier diodes.
Over-current Detection
Over-current detection is done via components 3U07, 3U08,
3U82, 3U83, and 2U18 for the 3.3 V converter and 3U09, 3U10,
3U96, 3U97, and 2U12 for the 1.2 V converter.
Under-voltage Detection
There is an additional circuit (7U10 and 7U11) to switch "off"
the 3.3 V converter in case the +12VS drops below 9 V.
Service Tips
• When a power MOS-FET is found defective, replace the
other power MOS-FET and fuse 1U01 as well.
• For a normal operation of the converter, it is important to
check the switching frequency, the value of the boost
voltage, and the amplitude of the gate voltage of transistor
7U04 (it should be close to the boost voltage).
9.2.10 V Generator
TUN
The +VTUN supply voltage (value 31...35 V at 4 mA) for the
analog tuner(s) is generated by a boost converter. It uses the
incoming +12 V and the pulses have a duty cycle of about
DC
10% from those of the 1.2 V DC/DC converter.

9.2.11 8V6 Switch

• Provides the +8V6-SW supply voltage from the incoming
+8V6.
• It is activated by the ON-MODE signal, which is active
"low". This is needed to switch "off" the +8V6-SW in POD
Stand-by mode, to lower the power consumption.
Note: It is not active if the +5V voltage is not present.
and load R , while the lower MOSFET
L
BJ2.4U/BJ2.5U LA

9.2.12 Useful Data

Voltage Name
+5V2
+5V
+8V6
+12VS
+VTUN
+1V2
+2V5
+2V5D
+3V3
+5V2S
+8V6-SW
+12VSW
*) ON mode (STAND-BY mode)
9. EN 153
Value [V] Tolerance [%]
5.2 5
5.1 5
8.6 5
12 5
33 5
1.26 3
2.6 4
2.6 (2.5) * 4 (5) *
3.3 5
5.1 5
8.6 5
12 5