JPH0560109B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a so-called CRT display device using a cathode ray tube that can display output information of a computer system and also display television images, and particularly relates to a so-called CRT display device that uses a cathode ray tube and can display output information of a computer system. The present invention relates to a method for switching the screen display range between when displaying television images and when displaying television images.

With the development of a highly information-oriented society, various information transmission systems such as INS and Captain have started to be put into practical use, and these systems use CRT display devices as a means of displaying information. .

Furthermore, each home is now equipped with a personal computer or the like in addition to a television receiver, and there is a tendency for a large number of CRT display devices to be installed in homes. Therefore, it is required that this CRT display device can be used in common.

By the way, as shown in FIG. 5, the display range on the screen is different when displaying output information from a normal computer system and when displaying a television image.

That is, as shown in FIG. 5a, the display screen of a CRT display device needs to have a smaller screen area than the displayable area of a cathode ray tube in order to display the output information of a computer system. is smaller than the displayable area 1, and as shown in FIG. 5b, the television image is overscanned and the display screen area 4 is larger than the displayable area 2.

Therefore, in the case of displaying output information from a computer system and displaying television images, it is necessary to switch the display range of the screen, but it is desirable that this switching method be simple and economical.

[Conventional technology]

FIG. 6 is a block diagram showing an example of a conventional screen display range switching circuit.

A deflection coil 9 is attached to the cathode ray tube 8 which is supplied with an anode voltage from the high voltage power supply circuit 7.
Deflection power is applied from a vertical deflection circuit 5 and a horizontal deflection circuit 6, respectively. If the magnetic flux density generated in the deflection coil 9 by this deflection power is B, then the electron beam 11 emitted from the cathode is deflected in proportion to the magnetic flux density B.

Since the magnetic flux density B is proportional to the deflection power applied to the deflection coil 9, if the maximum deflection amount of the electron beam 11 from the center of the cathode ray tube 8 is Y, then
This maximum deflection amount Y is proportional to the deflection power.

Conventionally, when switching the maximum deflection amount Y of the cathode ray tube 8 depending on whether output information of a computer system or television image is displayed, the switch 10 is switched to reduce or enlarge the drive signals of the vertical deflection circuit 5 and the horizontal deflection circuit 6. This was achieved by reducing the deflection power when shrinking, and increasing the deflection power when enlarging.

[Problem that the invention seeks to solve]

As mentioned above, conventionally, the information display screen area is reduced or expanded by increasing or decreasing the deflection power, so power consumption increases during overscan, and power is required for the vertical and horizontal deflection circuits and this deflection circuit. There is a disadvantage that the power supply device to be supplied is expensive.

[Means for solving problems]

The problem described above is that in a device that displays information by changing the display screen area of a cathode ray tube, the output voltage value of the power supply circuit that supplies the voltage applied to the anode of the cathode ray tube can be differentiated between the normal voltage value and a lower voltage value. The screen according to the present invention is provided with a voltage switching means for switching and outputting the output information, and the anode voltage value when displaying output information of a computer system is set higher than the anode voltage value when displaying a television image. This problem is solved by a display range switching method.

[Effect]

In other words, the display screen area of a cathode ray tube expands when the anode voltage decreases when the deflection power of the deflection coil is held constant. The anode voltage is supplied at a lower level than when displaying information.

〔Example〕

FIG. 1 is a block diagram of a circuit showing one embodiment of the present invention.

In this embodiment, the output voltage of the voltage power supply circuit 12 is switched between overscan and underscan.
During overscan, it is lowered than when underscan.

When displaying output information from a computer system, switch 10 is set to underscan.
is connected to the reduction side, and the high voltage power supply circuit 12 sends out the normal anode voltage.

Deflection power is applied to the deflection coil 9 of the cathode ray tube 8 from a vertical deflection circuit 13 and a horizontal deflection circuit 14, respectively, and the electron beam 11 is deflected from the center of the cathode ray tube 8 as shown by the maximum deflection amount Y.

When displaying a television image, the switch 10 is switched to the enlargement side to overscan. The high voltage power supply circuit 12 uses this enlarged signal to lower the normal anode voltage and supply it to the cathode ray tube 8. Since the relationship between the maximum deflection amount Y and the anode voltage E is Y∝1/√, the maximum deflection amount Y' increases as shown by the dotted line.

FIG. 2 is a block diagram of a circuit showing an embodiment of the anode voltage switching means of the present invention.

A drive signal is applied to the base of the transistor Q3 from the terminal F, and the transistor Q3 is repeatedly turned on and off by this drive signal. A voltage is applied from the power supply V to the collector of the transistor Q3 via the transistor Q1 and the primary winding of the flyback transformer T. Therefore, a high voltage pulse waveform is generated in the secondary winding of the flyback transformer T, which is rectified and supplies high voltage power to the anode of the cathode ray tube 8.

Diode D, capacitor C and transistor Q3 together with the primary winding of flyback transformer T constitute a circuit for generating a flyback pulse voltage.

The anode voltage supplied to the cathode ray tube 8 is resistor R3,
The voltage is divided by a voltage dividing circuit composed of a variable resistor RV and a resistor R2, and is fed back to the differential amplifier 15.
The differential amplifier 15 serves as a regulation circuit that compares the voltage of the power supply V with the feedback divided voltage, controls the base voltage of the transistor Q1, and adjusts the voltage supplied to the primary winding of the flyback transformer T. Operate.

The output of switch 10 shown in FIG. 1 enters from terminal A and switches the base voltage of transistor Q2. Therefore, since the resistance value of the sum of the resistor R1 connected in parallel to the resistor R3 and the internal resistance of the transistor Q2 changes, the comparison voltage of the differential amplifier 15 changes. The differential amplifier 15 controls the transistor Q1 according to the change in the comparison voltage, and switches the anode voltage of the cathode ray tube 8.

FIG. 3 is a circuit diagram showing another embodiment of the anode voltage switching means of the present invention, and FIG. 4 is a diagram illustrating the waveform of the flyback pulse at point G in FIG.

As explained in FIG. 2, the transistor Q3 repeats on/off, and current flows from the power supply V to the primary winding of the flyback transformer T1 via, for example, the contact 16 of the relay, and the flyback transformer T1
A high voltage is generated in the secondary winding of the cathode ray tube 8 and is supplied to the anode of the cathode ray tube 8.

An intermediate tap is provided on the primary winding of the flyback transformer T1 and is connected to the contact 16. The relay contacts 16 are operated by the output of the switch 10 in FIG. 1, and are connected in the direction shown by the solid line for reduction, and in the direction shown by the dotted line for enlargement.
In the case of magnification, the voltage occurring at the secondary winding of the flyback transformer T therefore decreases and a lower anode voltage is supplied to the cathode ray tube 8.

As explained in FIG. 2, with the capacitor C and the inductance L of the primary winding of the flyback transformer T1, the period Th of the drive signal is determined as shown in FIG.
A flyback pulse with a pulse width Tf = π√ is generated in synchronization with . The peak value Vp of this flyback pulse has the relationship Vp∝(Th/Tf), and by changing the pulse width Tf, the peak value Vp
can be changed.

This can be realized by changing the capacitance of capacitor C. The relay contact 17 is operated by the output of the switch 10 in FIG. 1, and in the case of reduction, the contact is open as shown by the solid line. In the case of enlargement, the contact points are closed as shown by the dotted line.

When contact 17 closes, capacitor C1 is connected in parallel to capacitor C, so the capacitance of the capacitor increases and the peak value Vp of the flyback pulse decreases. Therefore, the high voltage generated in the secondary winding of the flyback transformer T1 also decreases, and the cathode ray tube 8
The anode voltage supplied to decreases.

〔Effect of the invention〕

As explained above, the present invention switches the output voltage of the high-voltage power supply circuit and supplies it to the anode of the cathode ray tube, thereby changing the dimensions of the display screen area. There is almost no change in power consumption due to a change in the output voltage of the circuit, and the voltage of the high-voltage power supply circuit can be easily switched, making it possible to provide an economical screen display range switching system.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a circuit showing an embodiment of the present invention, Fig. 2 is a block diagram of a circuit showing an embodiment of the anode voltage switching means of the invention, and Fig. 3 is a block diagram of a circuit showing an embodiment of the anode voltage switching means of the invention. 4 is a diagram explaining the waveform of the flyback pulse at point G in FIG. 3, FIG. 5 is a diagram explaining the screen display range, and FIG. 6 is a diagram showing the conventional screen display. FIG. 3 is a block diagram showing an example of a range switching circuit. In the figure, 5, 13 are vertical deflection circuits, 6, 1
4 is a horizontal deflection circuit, 7 and 12 are high voltage power supply circuits, 8
is a cathode ray tube, 9 is a deflection coil, 10 is a switch, 11 is an electron beam, 15 is a differential amplifier, T,
T1 is a flyback transformer, Q1, Q2, Q3
is a transistor.

Claims (1)

[Claims] 1. In a device that displays information by changing the display screen area of a cathode ray tube, the output voltage value of a power supply circuit that supplies the voltage applied to the anode of the cathode ray tube is divided into a normal voltage value and a lower voltage. The screen is characterized in that it is provided with a voltage switching means for switching between the output values and the output values, and the anode voltage value when displaying the output information of the computer system is set higher than the anode voltage value when displaying the television image. Display range switching method. 2. The screen display range switching system according to claim 1, wherein the voltage switching means switches the control voltage value of a regulation circuit that adjusts the primary side voltage of the flyback transformer. 3. The screen display range switching system according to claim 1, wherein the voltage switching means switches a tap of a primary winding of a flyback transformer. 4. The screen display range according to claim 1, wherein the voltage switching means switches the capacitance of a capacitor connected in series to the primary winding of the flyback transformer, and shifts the resonance frequency with respect to the drive signal frequency. Switching method.