الدارة الترانزستورية للتكبير الراسي .. كتاب التلفزيون الملون والعادي

Chapter Fifteen:

vertical output deflection circuits

introduction :

The vertical deflection output circuits provide the necessary current to operate the vertical deflection coils during the scanning process - this circuit amplifies the output signal of the vertical oscillator to the extent necessary to operate the deflection coils - it also flows the waveform so that the current passing through the deflection coils is given a linear vertical sweep - the output voltage The feedback is given to the amplifier output of the stimulus circuits to confirm the linearity of the sawtooth wave, and the vertical deviation output circuits provide erasing pulses to blur the trace of return lines after the completion of scanning each field of the image. The three that wipe the screen.

The valves played the main role in these circuits. But now transistors or integrated circuits do this - especially since they are the best in the field of amplification.

​15-1 Transistor circuit for vertical amplification:

Figure (1-15) shows the box diagram of a typical transistor vertical output circuit. The sawtooth wave coming from the vertical oscillator passes through the primary amplifier to the output, then the deflection coils operating stage in order to secure the necessary gain to drive the vertical deflection coils. The amplification stage also includes a circuit to correct the waveform. Adjusting the linearity in the bias circuit of the primary amplifier stage - As for adjusting the height, it is found in the entrance to the circuit of the primary amplifier - and this adjustment is directed to the input signal, and the linearity is corrected by the feedback of the deflection files - and the stimulus stage also provides the vertical extinguishing pulses.

The feedback network is found in some vertical output circuits and feeds the entrance of a valve or the output transistor with part of the output signal. In this way, we maintain the height of the sawtooth wave in a uniform manner, thus ensuring the linearity of the magnetic field for the necessary deviation in the coils.

As for the vertical yolk impulses, they are produced in the output stage. It generates pulses that are applied to the screen valve control grid, or to the cathode, to interrupt the scanning beam through the return vertical.

Vertical output circuit in color TV:

In the vertical output circuit of the color TV, there are two additional tasks for this circuit that do not exist in the analogous circuit in the monochrome TV, and they are the circuit of correcting the phenomenon of pins and convergence or motor matching (Fig. 2-15). The circuit related to correcting the pincushion phenomenon is required by the screen valve with a large angle of deviation, and the circuit related to the kinetic convergence is required by many colored devices.

The beam switch on the box diagram is to turn off the vertical output amplifier for easier grayscale adjustment.

15-2 Correcting the pincushion phenomenon:

The pincushion phenomenon is more evident in the large screen with a large deviation (110). Figure (3-15), especially in the four sides of the linear structure of the image. This distortion is due to the fact that the surface of the screen has the same diagonal distance from the center of the electronic beam, so the surface of the screen is flatter - the beam cuts off A greater distance when scanning the edges of the screen than its center, especially in the four corners - and this requires correction of this distortion that resembles a pincushion, and the correction includes both horizontal and vertical deviation.

The principle of correction is based on the application of an equivalent cutting voltage added to the vertical output of a saw wave that operates the vertical deviation coils. The vertical sawtooth wave changes with the parabolic wave at the horizontal scan rate, so it increases in the vertical deviation in the middle up and down the screen in order to compensate for the curvature in the horizontal scan lines - and in the tuning keys it is possible to reach the best and accurate tuning to correct the wave. The circuit that corrects the pincushion phenomenon will be explained later .

Vertical alignment:

​​In a previous chapter, we learned that the motion convergence or convergence circuit works on the convergence of the three rays to tend to coincide on the surface of the screen. A parabolic wave formed in a special circuit is applied to the vertical motion matching circuit to perform this task. The proximity coils in the vertical output transformer (VOT) provide the sawtooth voltage to operate the circuits. A wave from the saw coming from the vertical output transformer (VOT) changed by the parabolic wave, then applied to the matching coils mounted on the deflection coils around the neck of the screen, and provided with controls to control the amplitude and phase of the sawtooth voltage. As well as a parabolic wave. Exactly, the current passing through the matching coils generates a magnetic field close to the three rays at the ends of the linear structure (raster). Kinetic matching will be explained in more detail in due course