JPS61171040A - Electromagnetic focusing temperature compensation device - Google Patents

Abstract

PURPOSE:To almost completely compensate for the increase and decrease in the magnetic flux of a focusing magnet due to the change in temperature, by disposing a temperature sensor near the focusing magnet, and controlling a direct current applied to an auxiliary focusing coil. CONSTITUTION:When the temperature of a diode D1, which serves as a temperature sensor, has gone up together with that of a magnet, an electrical current flowing through the diode increases and an electrical current applied to one input terminal of a differential amplifier OP1 decreases, so that the output of the amplifier rises. As a result, the output of a differential amplifier OP2 provided with a negative feedback circuit falls so that an electrical current i applied to an auxiliary focusing coil LM1 decreases. For that reason, a focusing magnetic flux can be kept almost constant within a practical temperature range from 20 deg.C to 70 deg.C if the initial value of the direct current applied to the auxiliary focusing coil LM1 and variable resistances VR1, VR2 are preset.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electromagnetic focusing device that focuses an electron beam emitted from a cathode of a picture tube or a picture tube, for example, and particularly relates to a picture tube for a projector. This invention relates to a temperature compensation device for an electromagnetic focusing magnet provided in a neck portion.

[Conventional technology]

FIG. 5 is a schematic diagram showing an example of a conventional electromagnetic focusing device, where LM1 is an auxiliary focusing coil for direct current, LM2
is an AC auxiliary focus coil, M is a picture tube (CRT)
) is a focusing magnet made of, for example, ferrite, and S is a shunt magnet wound around the outer periphery of the focusing magnet M.

Such an electromagnetic focusing device is called a picture tube (hereinafter referred to as CRT).
In order to form an optimal focus state on the entire phosphor screen of the phosphor screen, a DC component correction current is supplied to the auxiliary focus coil L M + , and an AC dynamic focus current that changes depending on the deflection position of the electron beam is applied to the auxiliary focus. The electron beam is supplied to the coil LM2 so that the electron beam is correctly focused at each part around the image receiving surface.

However, there is a problem in that the magnetic flux of the main magnet (M) that performs such electromagnetic focusing changes depending on the surrounding temperature, and as a result, the focus of the electron beam focused on the image receiving surface of the CRT changes.

Therefore, in order to improve this situation, as shown in FIG.
A band of a magnetic shunt section S having temperature-magnetic flux characteristics opposite to that of ferrite is wound around the magnetic flux to offset changes in magnetic flux caused by temperature changes.

[Problem that the invention seeks to solve]

In the conventional electromagnetic focusing device as described above, the temperature compensation method of winding the magnetic shunt part S around the focusing magnet M made of ferrite has a certain effect, but it suppresses the variation in magnetic flux to within about 1%. However, in TV receivers that require high resolution, a decrease in resolution remains a problem.

Further, even when an expensive rare earth magnet with constant temperature-magnetic flux characteristics is used, the temperature characteristics may be worse than a ferrite magnet with a magnetic shunt part S wound around it depending on conditions.

The present invention was made in order to solve such problems, and it is an object of the present invention to provide a temperature compensator that almost completely compensates for increases and decreases in magnetic flux due to temperature changes.

[Means for solving problems]

A temperature compensation device for electromagnetic focusing according to the present invention includes a temperature sensor placed close to a focusing magnet, and a direct current supplied to an auxiliary focusing coil based on changes in the magnetic flux of the focusing magnet caused by temperature changes. be compensated by.

[Effect]

In this invention, the temperature of the focusing magnet is detected by a temperature sensor placed on the focusing magnet, and changes in magnetic flux due to temperature changes are compensated for by controlling the DC current supplied to the auxiliary focusing coil. 7'''5, high resolution 460-
56.J [Embodiment] FIG. 1 is a schematic diagram showing an embodiment of the electromagnetic focus compensation device of the present invention, and the same parts as in FIG. 5 are designated by the same reference numerals. T is a temperature sensor fixed on the surface of the magnet M. The output of this temperature sensor T is input to an amplifier A that supplies a current for correction to an auxiliary focus coil M1, and the magnetic flux B of the magnet M is changed depending on the temperature. It is configured to supply a compensation current in the event of a fluctuation.

FIG. 2 shows an embodiment of the circuit diagram of the electromagnetic focus compensation device of the present invention, in which 10 is a compensation current consisting of a diode DI serving as a temperature sensor, variable resistors VRI, VH2, resistors rl-r3, etc. This is a setting circuit.

Note that VRI is a variable resistor for adjusting the temperature-current characteristics of the diode DI, VH2 is a variable resistor for setting the DC current value for electromagnetic focusing, OPI, OF2
is a driving differential amplifier for supplying direct current to the auxiliary focus coil LM; in particular, the differential amplifier OP2 is supplied with a feedback voltage by a resistor RF.

Since the electromagnetic focus temperature compensator of the present invention is configured as described above, in a commonly used dynamic focus device, the magnetic flux B of the focusing magnet M made of ferrite etc. 1. For example, if the temperature changes as shown in curve B in Fig. 3 within the range of 20°C to 70°C, the auxiliary focus coil LM
The magnetic flux for focusing can be kept constant by controlling the DC current supplied to I, for example, as shown in i in FIG.

In other words, when the temperature of the diode DI, which is the temperature sensor in this device, increases with the temperature of the magnet,
The current flowing through the diode DI increases and the differential amplifier OF
The output of the differential amplifier OF+ increases as the current supplied to one + input terminal decreases.

Therefore, the differential amplifier OP in which a negative feedback circuit is formed
The output of 2 decreases, and the auxiliary focus coil L M +
The current I supplied to the current I decreases as shown in FIG. 3 described above.

Therefore, the initial value of the DC current supplied to the auxiliary focus coil LM+ and the variable resistor VRI.

By adjusting VH2, the magnetic flux for focusing can be kept almost constant within the practical range of 20°C to 70°C.

Temperature sensor, material of focusing magnet M, and CRT
It is also assumed that the overall temperature-compensation characteristics, including the electrode structure, etc., change non-linearly.

FIG. 4 shows a block diagram of an electromagnetic focus temperature compensator which is another embodiment of the present invention that is effective in such cases, where 11 is a temperature sensor installed near the focusing magnet M, and 12 is a temperature sensor installed near the focusing magnet M. An A/D converter 13 converts the temperature detected by the temperature sensor 11 into a digital value, and a ROM (Rea) that stores an output current value for each input temperature information.
dOnlyMemory) 14, and ROM1
This is a compensation current setting circuit consisting of a D/A converter 15 that converts the digital output from 4 into an analog value.

OF++ and OPB are differential amplifiers, and LMI is a DC auxiliary focus coil.

In the apparatus of this embodiment, the temperature of the focusing magnet M is detected by a temperature sensor placed near the focusing magnet M, and is input to the ROM 14 via the A/D converter 13.

This ROM 14 stores data that determines the optimum correction current value at each temperature from the temperature-magnetic flux characteristics of the magnet M.

This output value is converted into a direct current by the D/A converter 15, and then supplied to the auxiliary focus coil LM+ via the differential amplifiers OF and OF+2.

In this way, this temperature compensator uses temperature sensors 11. By pre-recording data on the optimum correction current value determined from the temperature-magnetic flux characteristics of the focusing magnet (and focusing magnet) M in the ROM 14, good focusing can be achieved even when the temperature-magnetic flux characteristics of the focus of the electron beam are complex. condition can be maintained.

In the second embodiment, for example, the knee □□ in the electron gun
,,,Il,1Nio,7. -It is possible to compensate for errors, errors, and errors, and if the compensation data stored in the ROM can be input into a computer simulation system, it will be possible to correct various types of TV receivers. will be available for use.

〔Effect of the invention〕

As explained above, the present invention detects the temperature of the focusing magnet using a temperature sensor placed close to the focusing magnet, and controls the DC current supplied to the auxiliary focusing coil based on changes in magnetic flux due to temperature changes. Therefore, it is possible to almost completely compensate for the focus shift.

Additionally, when the correction information is stored in the ROM, by replacing the ROM, it is possible to perform temperature compensation for the focusing magnet with all temperature-magnetic flux characteristics and the electrodes in the electron gun. Not only can this be done, but it also has the effect of being inexpensive.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an electromagnetic focus compensator according to an embodiment of the present invention, Fig. 2 is a circuit diagram of the electromagnetic focus compensator of the present invention, Fig. 3 is a temperature characteristic diagram, and Fig. 4 is a diagram of the electromagnetic focus compensator of the present invention. A block diagram showing another embodiment, and FIG. 5 is a schematic diagram showing an example of a conventional electromagnetic focusing device. In the figure, 10 is a compensation current setting circuit, 11 is a temperature sensor, 1
2 is a compensation current setting circuit, 13 is an A/D converter, and 14 is R
OM, 15 is D/A variable mW, OF r + OP 2
*OP 1+ + and OF, 2 are differential amplifiers, Dl
is a diode, and L M + is an auxiliary focus coil. Figure 1A Figure 2Figure 3

Claims (1)

[Claims] a temperature sensor that detects the temperature of the electron beam focusing magnet; a compensation current setting circuit that outputs a signal corresponding to the temperature fluctuation detected by the temperature sensor; and a compensation current setting circuit that outputs a signal corresponding to the temperature fluctuation detected by the temperature sensor. An electromagnetic focus temperature compensation device characterized by comprising an amplifier circuit that supplies current to an auxiliary focus coil attached to a focusing magnet.