Line scanning, also known as horizontal scanning, line scanning circuit, is an electronic display technology. In the electronic fluorescent screen, when the sawtooth current of the horizontally placed line deflection coil is given, the vertical deflection magnetic field can be generated, forming the horizontal deflection force, so that the electron beam can scan along the water square.The relevant circuit used to generate line scanning is the line scanning circuit.
Provide sawtooth current for the line deflection coil;Provide working power supply and reverse travel pulse for other relevant circuits.
working principle
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Figure 4-1
Line scanning is also called horizontal scanning. Figure 4-1 shows the schematic diagram of line scanning process.
In the figure, two ATMEGA88V-10PU horizontal deflection coils are symmetrically placed at the top and bottom, and a specific sawtooth current is applied to the coil. The energized coil will generate a magnetic field.The right hand rule can be used to judge the direction of the magnetic field, that is, the four fingers point to the direction of the current, and the thumb points to the direction of the magnetic field. The current direction in the figure is consistent with the direction of the magnetic field, and the magnetic field direction is vertical and upward. When the current direction is opposite, the magnetic field direction is still vertical but downward.
The electron beam passes through a vertical magnetic field and is deflected horizontally by the magnetic field.The direction of force deflection of the electron beam in the magnetic field can be judged by the left hand rule, that is, the palm is in the direction of the magnetic field, the four fingers point to the direction of motion of the electron beam, and the thumb points to the direction of force deflection of the electron beam.The deflection direction of the electron beam is left when the magnetic field direction is upward;When the scanning current is opposite and the magnetic field is from top to bottom, the deflection direction of the electron beam is to the right.
(1) When the line scanning current is zero, there is no deflection magnetic field, the electron beam is not affected by the magnetic field, and the electron beam is only hit at the center 0.
(2) When the line scanning current is the maximum, the electron beam is biased to the left endpoint l.
(3) When the line scanning current is reverse and maximum, the electron beam is biased to the right end point 2.
Figure 4-2
The result is that when the line scanning current changes in size and direction, the electron beam deflects left and right in the horizontal direction to achieve line scanning.
Figure 4-2 shows the specific trajectory diagram of one line scanning. When horizontal scanning, the electron beam bombards each fluorescent spot on this line to make it glow.Due to the high frequency of line scanning and visual inertia, the same fluorescent spot (pixel) is constantly bombarded. As long as the time interval between two bombardments is less than the visual inertia time, this fluorescent spot seems to be emitting all the time.Each fluorescent spot on a line is emitting light in the same way, so the result of line scanning is to produce a horizontal bright line.
The line scan circuit includes line drive circuit, line output circuit, line reverse transformer (also called line output transformer) and medium and high voltage forming circuit.
The main function of the line scanning circuit is to provide a good linear sawtooth current to the line deflection coil, form a vertical linearly growing magnetic field, and control the electron beam to scan in the horizontal direction.At the same time, the pulse voltage formed during the travel reverse travel is used to provide the CRT with screen voltage, anode voltage, focusing electrode voltage, ABL sampling voltage, CRT filament voltage, video amplifier supply voltage, travel AFC comparison voltage, etc. through the high voltage, medium voltage and low voltage formed by the step up and step down of the travel reverse travel transformer.
The line scan circuit is the key circuit of the color TV. It works in the state of high frequency, high voltage and high current. Its power consumption accounts for about 70% of the power consumption of the whole machine. The color TV failure is related to the line scan circuit, which accounts for about 65%. Therefore, its working stability and reliability have a great impact on the stability and reliability of the whole machine.[1]
