JPH03104381A - Horizontal dynamic focus circuit - Google Patents

Abstract

PURPOSE:To obtain a sharp picture without defocusing at both left and right ends by using a saturable reactor biased with a DC magnetic field. CONSTITUTION:A saturable reactor 24 biased with a DC magnetic field is connected to the circuit, a DC bias is set so that a sawtooth wave current is decreased at the start of the scanning period and increased at the latter half by utilizing the self-inductance due to the saturation of each point of the sawtooth wave current flowing thereto. Since deformed waveform at the latter half of the scanning period of the sawtooth wave current supplied to a capacitor 3 is corrected, the phase deviation in a parabolic voltage is eliminated and a clear picture without defocus at both left and right edges of the picture is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention 1 (Industrial Application Field) The present invention is directed to the horizontal Regarding a dynamic focus circuit.

(Prior Art) Conventionally, a focus circuit of a television receiver or the like applies a direct current focus voltage to a focus electrode and focuses an electron beam with an electrostatic lens formed between the focus electrode and an anode electrode. As such a focus circuit, a so-called dynamic focus circuit is widely used, which superimposes parabolic voltages with a horizontal period and a vertical period on the DC focus voltage, in order to improve the focus characteristics at the periphery of the screen. There is. This is to compensate for the fact that the distance between the electron gun and the faceplate is different between the center and the periphery of the screen, so the optimal focus voltage is different, and to obtain a clear image with the entire screen in focus. It is something. Among dynamic focusing methods, horizontal dynamic focusing in particular has great effects and is widely used because the screen of a receiver is generally horizontally long.

FIG. 2 shows an example of a commonly used horizontal dynamic focus circuit. Horizontal choke transformer
Alternatively, a sawtooth wave current flows through the primary winding 1a of the flyback transformer 1 due to a horizontal uneven thickness circuit (not shown),
This current induces a horizontal pulse voltage in the secondary winding 1b.

This pulsed voltage is passed through a variable coil 2 that can vary the inductance to a capacitor 3 and a focus transformer 4.
is supplied to the primary winding 4a. Here, if the impedance of the variable coil 2 is sufficiently larger than that of the capacitor 3 and the primary winding 4a of the focus transformer 4, then
The current flowing through this variable coil 2 becomes a sawtooth wave. Then, if the capacitance of the capacitor 3 is sufficiently large and its impedance is sufficiently small with respect to the primary valley line 4a, most of the sawtooth wave current will flow through the capacitor 3, and both ends of the capacitor 3 will be (A parabolic voltage is generated. This parabolic voltage is transferred to the focus transformer 4.
The voltage is applied to the focus electrode of a CRT (not shown) through the secondary winding 4b and the coupling capacitor 5, superimposed on the focus voltage from the DC focus voltage generation circuit 6. Note that by changing the inductance of the variable coil 2, the amplitude of the sawtooth current can be changed and the amplitude of the parabolic voltage can be adjusted.

However, in an actual circuit, it does not necessarily operate as ideally as described above.What poses a particular problem is the influence of the DC resistance included in the variable coil 2.

FIG. 3 shows current and voltage waveforms at various parts in the circuit of FIG. 2. FIG. 3(a) shows the retrace pulse voltage appearing in the secondary winding 1b of the choke transformer 1, and this voltage ideally causes the variable coil 2 to move as shown in FIG. 3(b).
A sawtooth wave current flows as shown in the broken line. However, when the influence of the direct current resistance of the coil 2 is large, the waveform of the sawtooth current becomes distorted in the latter half of the scan interval, as shown by the solid line in FIG. 3(b). This collapse of the sawtooth wave affects the parabolic voltage in the form of a phase shift as shown in FIG. 3(C). Since the parabolic voltage shift time Δt shown in FIG. 3(C) is relatively small, it does not seem to pose a problem in practice.

However, the same amount of time (time width t) to the left and right from the center point of the screen
) ffi points A, A' [1]
The difference Δ■ in focus voltage between point and point A' appears as a value that cannot be ignored. However, in the past, in a normal CRT, there was a certain range of focus voltages that could be considered to be in the optimum focus state, and it was possible to make adjustments so that the entire screen fell within this range.

However, in recent years, many CRTs have been developed with improved focus characteristics at the periphery of the screen, and the above voltage difference Δ on both sides has been developed.
The defocus state caused by V is becoming clearer.

Therefore, in order to eliminate the phase shift of the parabolic voltage as described above, for example, a sawtooth wave generating circuit separate from the horizontal deflection circuit is provided, and the sawtooth wave is generated in phase with respect to the sawtooth wave in the horizontal deflection circuit. Possible methods include shifting the signal and using this to generate a parabolic voltage, and using a parabolic waveform generated by a more ideal signal processing circuit through a high-output amplifier. However, either method results in a significant cost increase, which is undesirable.

(Problem that Mitsume tries to solve) As mentioned above, in a horizontal dynamic focus circuit that generates a parabolic voltage using an integrating means using a coil and a capacitor, due to the phase shift of the parabolic wave due to the DC resistance of the coil, There was a problem in that the focus voltage was different between the left and right sides of the screen.

Therefore, the present invention is intended to solve the above problems.
It is an object of the present invention to provide a horizontal dynamic focus circuit that can obtain a correct parabolic waveform without phase shift using simple means and can obtain an optimal focus state over the entire screen.

[Structure of the Invention] (Means for Solving the Problem) The present invention inputs a horizontal periodic pulse voltage, integrates it using a coil and a capacitor, and flows a sawtooth wave current through the capacitor to generate a parabolic voltage. In a horizontal dynamic focus circuit that generates a state pressure and supplies the voltage to a focus electrode of a cathode ray tube together with a DC focus voltage, as the coil or connected in series to the coil,
It is characterized by the use of a saturable reactor biased with a DC magnetic field.

(Function) In the present invention, by using a saturable reactor, it is possible to correct the waveform distortion in the latter half of the scanning interval of the sawtooth wave current supplied to the capacitor, thereby eliminating the phase shift of the parabolic voltage and It is possible to obtain a clear image without defocusing at both the left and right ends.

(Example) The present invention will be described below based on the example shown in the drawings.

FIG. 1 is a circuit diagram showing a horizontal dynamic focus circuit according to an embodiment of the present invention.

In FIG. 1, the same parts as in the conventional example shown in FIG. 2 are given the same reference numerals. That is, a sawtooth wave current of a horizontal deflection circuit (not shown) is passed through a horizontal choke transformer (or flyback transformer) 1, and a horizontally periodic pulse voltage is applied from the secondary winding 1b to the saturable reactor 21. After obtaining a parabolic voltage by integrating it through an integrating means constituted by a capacitor 3 and a capacitor 3, it is boosted by a focus transformer 4, and superimposed on the DC focus voltage from a DC focus voltage generation circuit 6 through a coupling capacitor 5. The voltage is applied to a focus electrode of a CRT (not shown).

The difference between this embodiment and the conventional example is that instead of a variable coil for adjusting the amplitude of the parabolic wave, a saturable reactor (linearity correction coil) 21 biased with a DC magnetic field is connected, and a sawtooth current flows through this. Taking advantage of the fact that the self-inductance changes depending on the degree of saturation at each point of the wave current, the DC bias can be set so that the sawtooth wave current is small at the beginning of the scanning interval and becomes large at the latter half. This is to eliminate waveform collapse in the latter half of the wave scanning period.

The saturable reactor 21 has a structure in which a DC bias is applied to a core around which a coil is wound by a permanent magnet, and in FIG. 1, two saturable reactors 2Ia and 21b connected in series are used. Note that here, a combination of two saturable reactors with different characteristics (relationship between current and inductance) was used. In the saturable reactor 21 consisting of such two saturable reactors, the relationship between the current I and the inductance L is as follows, assuming that the direction of the arrow in the figure is the positive direction of the current, for example, when 1=+1A, L=200μ = When OA, L=170μ11 When 1--1A, threshold=145μ.

In addition, in Fig. 1, the capacitor 3 is the focus transformer 4.
The stray capacitance of the winding plays this role. It goes without saying that a normal capacitor as shown in FIG. 2 may be used.

In addition, in FIG. 1, a high voltage output circuit 6a that supplies high voltage to the anode of the CRT is used as the DC focus voltage generation circuit 6.
The output voltage is divided by a bleeder resistor 6b and outputted as a DC focus voltage.

In the circuit shown in FIG. 1 configured as described above, now the horizontal deflection frequency fl1=33,750 days Z(period)'J]T=
29.6μs>, and the sawtooth wave current flowing through the saturable reactor 21 is operated at approximately 2.4Ap-p (peak-to-peak value), the parabolic waveform generated as the secondary voltage of the focus transformer 4 is approximately 2.4Ap-p (peak-to-peak value). 0 0 VI
)-1). At this time, when Δt and ΔV (see FIG. 3) were determined from the parabolic waveform, the following results were obtained: Δ1=0 μs, ΔV=○V when t=5 μs, and ΔV=100 V when t=10 μs.

Next, for comparison, the amplitude of the parabolic waveform obtained on the secondary side of the focus transformer 4 is 2, When the voltage was adjusted to 400 V p-p and Δt and Δ■ were measured in the same way, when Δt=1 μs, ΔV=200V when t=5 μs, and ΔV=200V when t=10 μs.

As a result of the above, when a saturable reactor like the circuit shown in FIG. 1 is used, the phase shift of the parabolic waves is eliminated, so that the focus voltage difference Δ■ between the left and right sides of the screen can be made extremely small.

In the above embodiment, two saturable reactors 21a. Although the optimum characteristics are obtained by combining 2lb, it is also possible to obtain the optimum characteristics by combining a normal variable coil or fixed coil and a saturable reactor. Furthermore, it is of course possible to adjust the amplitude of the parabolic waveform by adjusting the magnet bias by optimally setting the characteristics (relationship between current and inductance) of the saturable reactor.

In this case, if it is used in a region where the magnet bias is relatively weak and saturation begins, the saturable reactor 21 can be configured with only one saturable reactor without using a normal variable coil or fixed coil. , the number of parts can also be reduced.

[Effects of the Invention] As described above, according to the present invention, with a simple configuration,
It is possible to prevent the phase shift of the parabolic waveform of the horizontal dynamic focus and the resulting imbalance between the left and right focus voltages, and to provide the optimum focus voltage for screen rest. Therefore, it is possible to obtain a clear image without defocusing at the periphery of the screen, especially at both left and right ends.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a horizontal dynamic focus circuit according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing a conventional horizontal dynamic focus circuit, and Fig. 3 is a circuit diagram showing voltages and currents in various parts of the circuit shown in Fig. 2. FIG. 1... Horizontal choke transformer (or flyback transformer), 3... Capacitor, 4... Focus transformer, 6
...DC focus voltage generation circuit, 21...Saturable reactor.

Claims (1)

[Claims] A horizontal periodic pulse voltage is input, this is integrated using a coil and a capacitor, a sawtooth wave current is passed through the capacitor to generate a parabolic voltage, and this voltage is applied to the focus electrode of the cathode ray tube together with a DC focus voltage. 1. A horizontal dynamic focus circuit, characterized in that a saturable reactor biased with a DC magnetic field is used as the coil or connected in series to the coil.