PHILIPS LC4.7E AA
Service Manual

EN 66

9.

LC4.7E AA

Circuit Descriptions, Abbreviation List, and IC Data Sheets
time in the linear region in between. Therefore, very little power is lost to heat. If the transistors have a low 'on' resistance (RDS(ON)), little voltage is dropped across them, further reducing losses. A Low Pass Filter at the output passes only the average of the output wave, which is an amplified version of the input signal. In order to keep the distortion low, negative feedback is applied (via R3723/3708). The advantage of Class D is increased efficiency (= less heat dissipation). Class D amplifiers can drive the same output power as a Class AB amplifier using less supply current. The disadvantage is the large output filter that drives up cost and size. The main reason for this filter is that the switching waveform results in maximum current flow. This causes more loss in the load, which causes lower efficiency. An LC filter with a cut-off frequency less than the Class D switching frequency, allows the switching current to flow through the filter instead of the load. The filter is less lossy than the speaker, which causes less power dissipated at high output power and increases efficiency in most cases. Mute A mute switch (item 7701) is provided at pin 6. This switch is controlled by the SOUND_ENABLE line from the Hercules (mute during operation). Protections Because of the symmetrical supply, a DC-blocking capacitor, between the amplifier and the speaker, is not necessary. However, it is still necessary to protect the speaker for DC voltages. Therefore, the following protections are therefore implemented: � Via R3765 and R3767, each stabilised supply voltage line is checked on deviations. � Via R3718 and 3717, each amplifier output is checked for DC-voltage.

On top of that, it can be further broken down into various systems depending on the region. The systems or region chosen, will in turn affect the type of sound standard that is/are allowed to be decoded. � For Europe, the standard consists of BG/DK/I/LL� for a Multi-System set. There are also versions for Eastern Europe and Western Europe and the standard for decoding will be BG/DK and I/DK respectively. � For NAFTA and LATAM, there is only one transmission standard, which is the M standard. The diversity then will be based on whether it has a dBx noise reduction or a NondBx (no dBx noise reduction). � For AP, the standard consists of BG/DK/I/M for a MultiSystem set. The diversity here will depend on the region. AP China can have a Multi-System and I/DK version. For India, it might only be BG standard. 9.8.2 Functionality The features available in the Hercules are as follows: � Treble and Bass Control. � Surround Sound Effect that includes: � Incredible Stereo. � � Incredible Mono. 3D Sound (not for AV Stereo).

� TruSurround (not for AV Stereo). � Virtual Dolby Surround, VDS422 (not for AV Stereo). � Virtual Dolby Surround, VDS423 (not for AV Stereo). � Dolby Pro-Logic (not for AV Stereo). � Bass Feature that includes: � Dynamic Ultra-Bass. � Dynamic Bass Enhancement. � BBE (not for AV Stereo). � Auto-Volume Leveler. � 5 Band Equalizer. � Loudness Control. All the features stated are available for the Full Stereo versions and limited features for the AV Stereo 9.8.3 Audio Amplifier Panel (diagram SA3) Introduction This panel contains the audio filters and amplifiers necessary for driving the speakers. The audio inputs come from the SSB (via connector 1739). The PSU delivers the positive and negative supply voltage of 16 VDC. After being filtered and amplified, the signals go to the speaker section, where the full range speakers are driven (load impedance is 8 ohm). Amplifier The amplifier is an integrated class-D amplifier (TDA7490). It combines a good performance with a high efficiency, resulting in a big reduction in heat generation. Principle Audio-power-amplifier systems have traditionally used linear amplifiers, which are well known for being inefficient. In fact, a linear Class AB amplifier is designed to act as a variable resistor network between the power supply and the load. The transistors operate in their linear region, and the voltage that is dropped across the transistors (in their role as variable resistors) is lost as heat, particularly in the output transistors. Class D amplifiers were developed as a way to increase the efficiency of audio-power-amplifier systems. The Class D amplifier works by varying the duty cycle of a Pulse Width Modulated (PWM) signal. By comparing the input voltage to a triangle wave, the amplifier increases duty cycle to increase output voltage, and decreases duty cycle to decrease output voltage. The output transistors of a Class D amplifier switch from 'full off' to 'full on' (saturated) and then back again, spending very little

9.9
9.9.1

Control
Hercules The System Board has two main micro-controllers on board. These are: � On-chip x86 micro-controller (OCM) from Genesis LCD TV/ Monitor Controller. � On-chip 80C51 micro-controller from Philips Semiconductors UOCIII (Hercules) series. Each micro-controller has it own I2C bus which host its own internal devices. The Hercules is integrated with the Video and Audio Processor. For dynamic data storage, such as SMART PICTURE and SMART SOUND settings, an external NVM IC is being used. Another feature includes an optional Teletext/Closed Caption decoder with the possibility of different page storage depending on the Hercules type number. The Micro Controller ranges in ROM from 128 kB with no TXTdecoder to 128 kB with a 10 page Teletext or with Closed Caption.

9.9.2

Block Diagram The block diagram of the Micro Controller application is shown below.