JPH09230815A - Heater drive circuit for cathode-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable heater drive voltage without regarding variation in a deflection frequency by providing a control system for keeping a horizontal deflection current flowing through a horizontal deflection coil to a fixed level and a current transformer detecting the current and lighting a heater of a cathode-ray tube with the current transformer. SOLUTION: Respective heater winding wires 7b-7d of the secondary side of the current transformer 7 are connected respectively to the heaters 12r, 12g, 12b of a direct heat type color cathode-ray tube 12. A flyback pulse generated on a secondary winding wire 2b of a matching transformer 2 is supplied to the horizontal deflection coil 8 through the primary winding wire 7a of the current transformer 7. Then, a peak voltage of a pulse generated on the horizontal deflection coil 8 is detected by a voltage detection circuit 14 to be supplied to a power amplifier circuit 16 through an addition circuit 15, and the closed loop is controlled so that the peak voltage of the pulse generated on the horizontal deflection coil 6 becomes the fixed level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device using a cathode ray tube such as a television receiver and a cathode ray tube display, and more particularly to a heater driving circuit for supplying a driving voltage to a heater of a direct heating type cathode ray tube. .

[0002]

2. Description of the Related Art For example, in a television receiver, it is desirable to display an image as short as possible after the power is turned on. However, since a general cathode ray tube is an indirectly heated cathode ray tube in which the cathode is heated by a heater, it has a slow start-up, and if no measures are taken, it takes several seconds to several tens of seconds until an image is displayed. Requires. For this reason, it is known that the heater of the cathode ray tube is preheated at a voltage lower than the regular voltage during standby and the regular heater voltage is applied when the power is turned on so that an image can be displayed immediately after the power is turned on. Has been.

However, it is not preferable from the viewpoint of energy saving to constantly heat the heater during standby. Therefore, it has been proposed to use a direct heating type cathode ray tube instead of the indirectly heating type cathode ray tube. In the direct heating type cathode ray tube, since the heater (filament) itself is an electrode for emitting thermoelectrons, it can start up in a short time without preheating.

In a direct heating type cathode ray tube, a video signal is applied to a heater which is a thermionic emission electrode to modulate an electron beam emitted from the heater, but the heater and the thermionic emission electrode are integrated. Therefore, it is necessary to insulate the power supply circuit for driving the heater from other electric circuits.

Therefore, in a conventional image display device using a direct heating type cathode ray tube, a heater winding is provided in a flyback transformer of a high voltage output circuit to divide a flyback pulse to turn on the heater. You are getting voltage.

[0006]

On the other hand, in a cathode ray tube display for a personal computer, it is necessary to switch the vertical and horizontal deflection frequencies according to the display mode. For example, in a DOS / V type personal computer, it is necessary to make the horizontal deflection frequency variable within the range of 30 to 78 kHz according to the display mode.

However, as described above, when the heater driving voltage is obtained from the flyback transformer, the peak value of the flyback pulse changes when the horizontal deflection frequency changes, and the voltage applied to the heater also changes. There is a problem that it ends up. Further, since the flyback pulse has a large peak value, there is a problem that it adversely affects the video signal applied to the heater.

Therefore, an object of the present invention is to provide a heater drive circuit which can obtain a stable heater voltage even when the horizontal deflection frequency changes. It is another object of the present invention to provide a heater drive circuit that does not adversely affect the video signal.

[0009]

A heater driving circuit for a cathode ray tube according to the present invention comprises a horizontal deflection circuit including a horizontal deflection coil,
A power amplifier circuit that supplies a power supply voltage to the horizontal deflection circuit and a control signal to the power amplifier circuit that detects the voltage generated in the horizontal deflection coil and keeps the voltage generated in the horizontal deflection coil constant. It is characterized by comprising a voltage detection circuit to be supplied and a current transformer whose primary winding is connected in series to the horizontal deflection coil and whose secondary winding is connected to the heater of the cathode ray tube.

The present invention is also characterized in that the horizontal deflection frequency is variable.

The present invention is also characterized in that the output of the voltage detection circuit and a horizontal deflection size adjustment signal are added and supplied to the power amplification circuit.

The present invention is also characterized in that the cathode ray tube is a direct heating type.

The present invention is also characterized in that the current transformer comprises a plurality of secondary windings insulated from each other.

[0014]

1 is a block diagram showing an embodiment of a horizontal deflection circuit of the present invention.

The collector of the horizontal output transistor 1 which is turned on and off in the horizontal cycle is supplied to the power supply terminal 3 through the primary winding 2a of the matching transformer 2 and also through the parallel circuit of the damper diode 4 and the resonance capacitor 5. Grounded.

A plurality of taps are led out to the secondary winding 2b of the matching transformer 2, fixed terminals 6a to 6g of the changeover switch 6 are connected to each tap, and between the movable terminal of the changeover switch 6 and the ground. A series circuit of the primary winding 7a of the current transformer 7 and the horizontal deflection coil 8 is connected. A series circuit of a coil 9 and a capacitor 10 is connected in parallel to this series circuit, and the cold end side of the secondary winding 2b of the matching transformer 2 is grounded via the capacitor 11. The changeover switch 6 is for matching the output impedances of the horizontal deflection coil 8 and the horizontal output circuit.

Three heater windings 7b, 7c and 7d are provided on the secondary side of the current transformer 7. Each heater winding 7b, 7c and 7d is a direct heating type color cathode ray tube 1.
The two heaters 12r, 12g, and 12b are respectively connected. The heater 12r is for generating a red electron beam, the heater 12g is for generating a green electron beam, and the heater 12b is for generating a blue electron beam. Each heater 12r, 12g, 1
2b includes video signal S corresponding to each color from the video output circuits 13r, 13g, and 13b corresponding to red, green, and blue, respectively.
r, Sg, Sb are supplied.

On the hot end side of the horizontal deflection coil 8, a voltage detection circuit 14 for detecting the peak voltage of the pulse generated in the horizontal deflection coil 8 is connected.
The output of the voltage detection circuit 14 is added to the DC horizontal deflection size adjustment signal in the addition circuit 15. Addition circuit 1
The output of 5 is amplified by the power amplifier circuit 16 and supplied to the power supply terminal 3 as a power supply voltage for the horizontal output transistor 1.

In the circuit shown in FIG. 1, since the horizontal output transistor 1 is turned on / off in a horizontal cycle, a sawtooth wave current having a horizontal cycle flows through the primary winding 2a of the matching transformer 2.

A flyback pulse proportional to the number of windings is generated in the secondary winding 2b of the matching transformer 2 as shown in FIG. 2 (a). This flyback pulse is a primary winding of the current transformer 7. It is supplied to the horizontal deflection coil 8 via the line 7a. Therefore, a horizontal sawtooth wave current, that is, a horizontal deflection current as shown in FIG. 2B flows through the horizontal deflection coil 8.

The peak voltage of the pulse generated in the horizontal deflection coil 8 is detected by the voltage detection circuit 14 and supplied to the power amplification circuit 16 via the addition circuit 15, and the peak of the pulse generated in the horizontal deflection coil 8 is detected. Closed loop control is performed so that the voltage is constant. Therefore, the horizontal deflection coil 8
The amplitude of the electric current flowing through is kept constant regardless of the deflection frequency.

For example, if the horizontal deflection frequency becomes low,
The cycle of the flyback pulse becomes long, and the peak value of the deflection current also increases if no measures are taken.
Here, in the present embodiment, the power supply voltage for the horizontal deflection circuit is lowered so that the peak voltage of the pulse generated in the horizontal deflection coil 8 becomes constant, so that the amplitude of the current flowing in the horizontal deflection coil 8 is always constant. Maintained at.

The horizontal deflection current flowing through the horizontal deflection coil 8 also flows through the primary winding 7a of the current transformer 7, and the secondary winding of the current transformer 7, that is, the heater windings 7b, 7c and 7d, is horizontally fed. A sawtooth voltage corresponding to the deflection current is generated. The sawtooth wave voltage obtained on each heater winding 7b, 7c, 7d is supplied to the three heaters 12r, 12g, 12b of the direct heating type color cathode ray tube 12, respectively. Therefore, the heaters 12r, 12g, 12b are turned on, and the electron beam can be emitted. Then, the amount of the electron beam from each heater 12r, 12g, 12b is modulated by the video signals Sr, Sg, Sb corresponding to each color from the video output circuits 13r, 13g, 13b, and the screen of the color cathode ray tube 12 (see FIG. An image of a predetermined color is displayed in (not shown).

In the above heater drive circuit, if the horizontal deflection frequency is switched, the cycle of the flyback pulse changes, but due to the above-mentioned closed loop control,
Since the amplitude of the horizontal deflection current is kept constant, the amplitude of the sawtooth wave voltage obtained in each heater winding 7b, 7c, 7d is also kept constant, and the heaters 12r, 12 of the cathode ray tube 12 are kept.
The voltage applied to g and 12b does not change. Therefore, even when the horizontal deflection frequency is switched,
The color cathode ray tube 12 can be stably operated.

[0025]

According to the present invention, the control system for keeping the horizontal deflection current flowing through the horizontal deflection coil constant is provided, and the current transformer for detecting the current flowing through the horizontal deflection coil is provided, and the output of this current transformer is provided. Since the heater of the cathode ray tube is turned on, a stable heater driving voltage can be obtained regardless of the change of the deflection frequency.

Further, since the waveform of the voltage applied to the heater of the cathode ray tube is a sawtooth wave, the heater can be turned on at a lower peak value than the flyback pulse, and the video signal applied to the heater can be changed. Has little adverse effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a horizontal deflection circuit of the present invention.

FIG. 2 is a waveform diagram showing a flyback pulse and a horizontal deflection current.

[Explanation of symbols]

1 ... Horizontal output transistor, 2 ... Matching transformer,
2a ... Primary winding, 2b ... Secondary winding, 3 ... Power supply terminal, 4 ...
Damper diode, 5 ... Resonant capacitor, 6 ... Changeover switch, 6a-6g ... Fixed terminal, 7 ... Current transformer, 7a ... Primary winding, 7b, 7c, 7d ... Heater winding, 8 ... Horizontal deflection coil, 9 ... Coil 10 ... Capacitor, 11 ... Capacitor, 12 ... Direct heating type color cathode ray tube,
12r, 12g, 12b ... Heater, 13r, 13g, 1
3b ... Video output circuit, 14 ... Voltage detection circuit, 15 ... Addition circuit, 15 ... Addition circuit, 16 ... Power amplification circuit 96-0

Claims (5)

[Claims] 1. A horizontal deflection circuit including a horizontal deflection coil, a power amplification circuit for supplying a power supply voltage to the horizontal deflection circuit, a voltage generated in the horizontal deflection coil is detected and generated in the horizontal deflection coil. A voltage detection circuit that supplies a control signal to the power amplification circuit so that the voltage is constant; and a primary winding of the voltage detection circuit connected in series to the horizontal deflection coil,
A heater driving circuit for a cathode ray tube, the secondary winding of which comprises a current transformer connected to a heater of the cathode ray tube. 2. A heater driving circuit for a cathode ray tube according to claim 1, wherein the horizontal deflection frequency is variable. 3. The heater drive circuit for a cathode ray tube according to claim 1, wherein the output of the voltage detection circuit and a horizontal deflection size adjustment signal are added and supplied to the power amplification circuit. 4. The heater driving circuit for a cathode ray tube according to claim 1, wherein the cathode ray tube is of a direct heating type. 5. The heater drive circuit for a cathode ray tube according to claim 1, wherein the current transformer comprises a plurality of secondary windings insulated from each other.