Power Supply Repair Guide - How to - Philips Chassis BP2.2U AA & BP2.3U AA Plasma TV PSU

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Philips Chassis BP2.2U AA & BP2.3U AA Plasma TV PSU

Tuesday, 05 January 2010

PHILIPS Chassis BP2.2U & BP2.3U Plasma TV Power Supply (PSU) circuit descriptions. This is a 42" & 50 inch plasma tv chassis.

Introduction

The Main Power Supply is a buy-in module (it belongs to the PDP), and therefore is a “black box” for Service. When defective, a new panel must be ordered and after receipt, the defective panel must be send for repair. This Power Supply delivers the following supply voltages to the chassis:

• +12VS.

• +8V6.

• +5V2.

• +5V.

As the VIPER and many other ICs on the SSB require low supply voltages at high current (up to 3 A for the main voltages), onboard DC/DC converters are implemented. The circuit on the SSP provides the 3.3 and 1.2 voltages. A DC/DC converter has the following advantages:

• The DC/DC converter is directly on the SSB near the circuits that needs to be powered.

• Some circuits on the SSB need high current by low voltage, so there is no risk to have power dips or voltage loss in connections between the PSU and the SSB panel.

Block Diagram

DC/DC converter block diagram

PSU Start-up Sequence

1. If the input voltage of the DC/DC converters is around 12V (measured on the decoupling capacitors 2U17/2U25/2U45) and the ENABLE signals are "low" (active), then the output voltages should have their normal values.

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

3. Then, after this voltage becomes present and is detected OK (about 100 ms), the other two voltages (+2V5 and +3V3) will be activated (via ENABLE-3V3).

4. The current consumption of controller IC 7U00 is around 20mA (that means around 200 mV drop voltage across resistor 3U22).

+2V5D Linear Stabilizer

• Provides the +2V5D voltage, and is derived from the +5V2-STBY voltage coming from the Main Power Supply.

• The output current is limited to a few tenths of mA.

• Output over-voltage protection is done by zener diode 6U17.

+12V Switch

• The +12V switch is activated when the POD-MODE signal is "low".

• The rise time of the output voltage is set by components 2U42, 3U43, and 3U95 at about 30ms.

• The switch "off" is fast, because there can be fault currents that must be interrupted.

• When the input voltage (+12VS) is higher than 15 V, the switch is disabled via circuit 6U12, 3U52, 3U53, 2U71, and 7U14-2.

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 overvoltage detector transistors 7U15-1, 7U15-2, 7U29-1, and 7U29-2.

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

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 7U03). 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 7U01 at the input side). The upper MOSFET TS1 conducts, to transfer energy from the input to the inductor L1 and load RL, 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 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).

VTUN Generator

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 VDC and the pulses have a duty cycle of about 10% from those of the 1.2 V DC/DC converter.

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.

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Last Updated ( Thursday, 07 January 2010 )