التغذية ذات التردد الأفقي .. كتاب التلفزيون الملون والعادي

12 - 12 Horizontal Frequency Feed:

Feeding through a transformer has some advantages and advantages that were previously mentioned, but it adds an important size and weight to the television set - and its current ripples are low-frequency (50 or 100 Hz). This is what requires existence. Capacitors add a large capacity, and some circuits need better filtering, which calls for the use of a choke coil.

We mentioned the possibility of extracting the feeding voltages (+B or –B) from the horizontal output stage.

Thus, we achieve the following advantages:

1- Reducing the weight and size of the receiver

2- Isolate the feeding line from the device.

3 - The aliasing frequency is often (15625 Hz), which simplifies the filtration and filtering process, and it is sufficient to use capacitors of smaller capacity. And reduces the need for filtration with a suffocating file.

Start-and-Run Efforts:
Most of the circuits in a color television set, including the horizontal oscillator circuit, are fed by derivative voltages - with the exception of the horizontal output transistor, which

It is fed from feed + B to generate the sub voltages - also the horizontal oscillator has to start working first and this is essential for the horizontal output transistor to receive its operating signal.

The starting voltages of the horizontal oscillator (buffer and driver) are generated quickly at the moment the device is turned on - these starting voltages are sufficient to initiate the operation of the horizontal oscillator (buffer and driver). After starting to work normally, the secondary derivative voltages ensure the continuation of this natural work (i.e. include the operating voltage Run) for these circuits, and so the horizontal output transistor is fed independently from the main supply circuit.

The feed circuit for the horizontal output stage:

The simplified circuit shows Figure (12-17) how the starting voltage + B is generated and how the horizontal output stage + B generates the derived voltages Note: The voltages derived from the horizontal output stage are isolated from the AC grid line - but the horizontal output feeder circuit is not isolated and for this The precaution is necessary to connect an isolation transformer on the AC line when repairing this type of equipment.

entrance circuit:

Alternating voltage is applied to the rectifier bridge circuit consisting of four diodes by way of file 201 L connected to a variable resistance with voltage (VR 20 (Varistor), which protects the rectifier bridge from current flows and transient currents, and the resistance 201 RF performs a fuse action, and serves as an additional protection for the rectification circuit It identifies peak currents and protects against load tripping and diode failure due to B+ overloading.

Calendar output:

The output voltage of the bridge circuit, applied to one winding of the starting transformer 201 T and then the throttle coil L403 - capacitor C304 provides additional voltage filtering
+ 150 volts, which is fed to the regulator circuit by the circuit breaker. The regulator output +110V feeds the horizontal output transistor collector circuit.

Organizing the feeding circuit:

In addition to the previously mentioned +110 volt regulator, all circuits of the colored device are mostly operated by regulated voltages, and in the diagram that we explain, we find that the voltage (+22 volts) is a regulator that feeds the picture board, and also feeds the horizontal oscillator, the voter, and the medium frequency (IF) board. And adjust the automatic composition (AFT) as well as feeding the color palette (Chroma). In the last panel, an additional voltage regulator (112 volts) is used. In using the solid elements of the regulation circuit described previously, we can work with the network voltage between 105 volts to 135 volts, or between (200) volts to 235 volts, and this is particularly important because the network voltage changes from one region to another and from moment to moment.

Start-up feed circuit

As shown in the circuit diagram (Fig. 12-17), during normal operation, the output of the 150-volt rectifier bridge circuit is fed through the primary coil of the starting transformer 403 L, and the filter capacitor C304. It applies to the horizontal regulator (+110 volts), and this is what happens at the moment of closing the main breaker S 4201 = ON/OFF

Charging capacitor C304 before closing the main circuit breaker - there is no current in the starting transformer 201 T or the filter coil 403 L, the filter capacitor C304 is completely empty and when the main circuit breaker 54201 is closed - the capacitor C304 appears as if it is short circuit, and a maximum current passes in the primary coils of the transformer 201 T and the coil 403 L and this transient current generates a voltage in the secondary coil of the transformer - and the polarity of the right end of the secondary coil 201 T is positive
The starting voltage of the secondary oscillator:

The starting transient voltage is 22 volts and is now applied via the starting diode 302 CR to the horizontal oscillator and this voltage is sufficient to start the oscillator and at this time the starting diode (301) (CR) is reverse biased the moment the 22 volt power is cut off.

Starting of the horizontal bumper and the stimulus (Buffer driver)

As in the previous paragraph, the starting voltage of 27 volts (bumper) and 24 volts (motivator) passes through the starting diodes 303-CR305-CR..but the CR304 is the operating diode. is reverse biased by the starting voltage - because the derivative branch voltage has not yet been generated. The starting voltage is sufficient for the primary and primary supply of the horizontal bumper circuit
And the stimulus.

The operating diodes 304,301, are in a state of reverse bias during the very short start-up period - and provide isolation between the starting and operating circuits - and when the derived (operating) voltages are in working condition, the starting diodes, CR305, CR303 CR302 become in the state of reverse bias and isolate the starting and operating feeding circuit .

Sub-voltage feed circuit:

After the circuit of the horizontal oscillator, the stimulus, and the buffer are fed from the starting circuits, the horizontal deviation output circuits begin to work. At this time, the operating circuits of the derived feed become in working condition, while the starting circuits stop until the time when the device is restarted after turning it off. As mentioned earlier, all circuits are fed from the derivative voltages, except for the horizontal output transistor. These circuits take their energy from the flyback transformer.


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