الدارة الكاملة لمرحلة الصوت بدارة ic واحدة وعناصر أخرى .كتاب التلفزيون الملون والعادي

12-18 Complete audio stage circuit with one IC and other components:

Many modern TV sets contain only one IC circuit for audio that includes all sound stages. In Figure (18-27) there is a type of circuit used and it contains 13 elements with a circuit (IC), which includes IF amplifiers - limiter - orthogonal detector - low-frequency amplifier optical.

This circuit requires an output transistor and an audio output transformer with a 4 ohm impedance of 2 watts.

Complete audio stage circuit with only one IC:

This integrated circuit includes the following circuits:

1- Specified (5.5MHz).

2- Orthogonal detector.

3- Electronic volume reducer.

4 - Power amplifier for the audio signal

5- Current limiter.

6 - Thermal protection system

7 - Voltage regulator, which is shown in the figure
(18-28).

circuit explanation:

This integrated circuit IC is used in color devices - which contains a synchronous video signal detector. The output of this type of detector does not contain the different heterodene frequencies that are found in the output of the diode. The frequency 55 MHz - the intermediate frequency IF of the sound can be extracted from the output of the preamplifier of the image signal - This provides a relatively high input signal to a specified circuit (55) megahertz (MHz) in the integrated circuit IC.

Limiter Detector:
We get the frequency of the IF audio 5.5 MHz from the coil 186 L - this signal is fed to the limiter via pole 10 of the IC - and the limiter is connected internally to the orthogonal detector - and the coil of the orthogonal detector (5.5 MHz) is connected to the two poles (14 and 15) and a circuit (deemphasis). Tone control is connected to pole 16.

Electronic Attenuator Capacity:

The audio signal output of the crosstalk detector is internally connected to the electronic audio attenuator (transistor). It is a pre-amplifier of the audio signal with controlled gain - and the amount of voltage of the audio signal passing through this reducer to the two amplifiers can be controlled with the R175 audio switch. The advantages of this method of control are that the audio control switch deals with DC current and not with the audio signal. This is what enables it to be placed anywhere without the use of shielded wires, so there is no fear of a hum in the sound due to the interference that occurs.