JPH0378030B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a horizontal deflection circuit including a horizontal oscillation time constant variable circuit having a configuration in which a time constant setting element can be switched.

(Prior Art) In display devices, there is a trend to increase the number of scanning lines by increasing the horizontal deflection fraction in order to improve screen resolution and obtain a flicker-free screen using a non-interlace method. Additionally, an underscan method is used to ensure that the entire image fits inside the screen. Therefore, the ratio Th/Tr between the horizontal period Th and the retrace period Tr is increasing.

By the way, the collector pulse voltage V _cp of the horizontal output transistor constituting the horizontal output circuit of the horizontal deflection circuit can be expressed by the following equation.

V _cp =V _cc {π/2(Th/Tr−1)+1} (1) where V _cc indicates the power supply voltage of the horizontal output transistor.

As is clear from equation (1), as the ratio Th/Tr between the horizontal period Th and the retrace period Tr increases, the collector pulse voltage V _cp also increases. Therefore, in order to improve the resolution and increase the image output period, it is necessary to reduce the retrace period, so it is necessary to use a transistor with high breakdown voltage characteristics as the horizontal output transistor.

Recently, a single display device has also been used as a terminal for computers with different horizontal scanning cycles, or as a terminal for a video camera using an NTSC signal frequency of 15.734 kHz.
For this purpose, a horizontal deflection circuit that performs horizontal scanning by switching between, for example, a data signal frequency of 24 kHz and an NTSC signal frequency of 15.734 kHz is required.

Figure 3 shows a conventional horizontal deflection circuit of this type.
A horizontal oscillation time constant variable circuit 11 is provided. This horizontal oscillation time constant variable circuit 11 includes a horizontal synchronizing volume 15 and a resistor 1 connected to a power supply terminal 13.
7. A charging time constant circuit consisting of a capacitor 19 for setting a time constant, the capacitor 19, a resistor 21,
The discharge time constant circuit includes a switching element 23. A capacitor 25 for varying the time constant and a switching means 27 for changing the time constant are connected in parallel to the capacitor 19. The time constant switching switching means 27 is opened and closed by a switching control signal from a frequency switching control signal generation circuit 29. A pulse shaping circuit 31 and a horizontal drive circuit 33 are connected to the output side of the horizontal oscillation time constant variable circuit 11. A horizontal output circuit 35 is connected to the output side of the horizontal drive circuit 33. This horizontal output circuit 35 has a horizontal output transistor 37, a damper diode 39, and a retrace capacitor 41, and a deflection yoke 45 is connected in parallel via a scanning capacitor 43. A power supply voltage variable circuit 49 for horizontal amplitude control is connected to the collector of the horizontal output transistor 37 via an output transistor 47, and the variable circuit 49 changes the voltage applied to the horizontal output transistor 37 from the power supply terminal 13. Further, a horizontal AFC circuit 51 is connected to the output side of the horizontal oscillation time constant variable circuit 11. This horizontal AFC circuit 51 is connected to the input terminal 12 via a high-pass filter 53 that removes vertical synchronizing signals, etc.
A 42kHz or 15.734kHz horizontal synchronization signal is input.

When the time constant switching means 27 is open, the time constant variable capacitor 25 is electrically disconnected from the capacitor 19.
The time constant of the horizontal oscillation time constant variable circuit 11 becomes smaller. Accordingly, when the capacitor 19 is charged from the power supply terminal 13 via the horizontal synchronization volume 15 and the resistor 17, when the switching element 23 opens and closes at a frequency of 24 kHz, the charging current of the capacitor 19 is transferred to the common side via the resistor 21. Since it flows to A
A sawtooth voltage is generated at the point with a horizontal deflection frequency of 24kHz. The sawtooth voltage is generated by the pulse shaping circuit 31.
It is shaped into a pulse signal by the horizontal drive circuit 3.
3 and then applied to the base of the horizontal output transistor 37 of the horizontal output circuit 35. The horizontal output transistor 37 becomes conductive when a pulse signal is input, and the damper diode 39 becomes conductive depending on the polarity of the voltage with which the retrace capacitor 41 is charged. The deflection yoke 45 has a large induction. Therefore, the deflection yoke 45 has
Sawtooth current flows at 24kHz.

On the other hand, the collector pulse voltage applied to the horizontal output transistor 37 is fed back to the horizontal AFC circuit 51. Therefore, this horizontal AFC circuit 51 compares the phases of the 24kHz horizontal synchronizing signal and the collector pulse voltage with its phase discriminator, outputs the AFC voltage to point A, and thereby horizontal oscillation time constant variable circuit 1
The oscillation frequency of 1 is phase-controlled by a horizontal synchronization signal.

Next, when a switching control signal is output from the frequency switching control signal generation circuit 29 and the time constant switching switching means 27 is closed, the time constant variable capacitor 25 is connected in parallel to the capacitor 19. Therefore, the horizontal oscillation time constant variable circuit 11
The time constant of becomes larger. Therefore, when the switching element 23 opens and closes at a frequency of 15.734kHz,
A sawtooth voltage is generated at point A with a horizontal deflection frequency of 15.734kHz. Therefore, as mentioned above, the deflection yoke 45 receives 15.734k from the horizontal output circuit 35.
Sawtooth current is supplied at Hz. Also, horizontal
Since a 15.734kHz horizontal synchronization signal is input to the AFC circuit 51, the phase of the horizontal oscillation time constant variable circuit 11 is stably controlled.

By the way, change the horizontal frequency Th from 24kHz to 15.734k
When switching to Hz, if the retrace period Tr is constant, the collector pulse voltage increases as the horizontal frequency Th increases, as is clear from equation (1) above.
V _cp increases. Therefore, it is necessary to reduce the power supply voltage V _cc in consideration of the withstand voltage of the horizontal output transistor.

On the other hand, the value of the sawtooth current I _ypr in the deflection yoke is
If the high pressure is constant, it can be expressed by the following equation (2).

I _ypr = V _cc (Th-Tr)/L (2) where L represents the inductance of the deflection yoke.

Now, when the power supply voltage _Vcc is reduced, the collector pulse voltage _Vcp becomes constant, and the horizontal amplitude of the screen also becomes constant. Furthermore, if the ratio Th/Tr between the horizontal period Th and the retrace period Tr is constant, then (1)
As is clear from the formula, the collector pulse voltage V _cp
is constant as shown in equation (3) below.

Th/Tr=K>1 (3) Here, by substituting equation (3) into equation (2), the following equation (4) is obtained.

I _ypr = V _cc (K-1) Tr/L ...(4) In this equation (4), K is constant, so if you switch the horizontal frequency Th from 24kHz to 15.734kHz,
Since the retrace period Tr becomes longer, it is necessary to reduce the power supply voltage V _cc in order to keep the horizontal amplitude of the screen (proportional to I _ypr ) constant.

Therefore, conventionally, the switching control signal from the frequency switching control signal generation circuit 29 is input to the power supply voltage variable circuit 49, and the power supply voltage V _cc at the power supply terminal 13' is stepped down by the power supply voltage variable circuit 49 to output the horizontal output transistor. I am trying to add it to 37. However, at the time when the horizontal frequency is switched from 24kHz to 15.734kHz, the power supply voltage variable _circuit 49 has transient characteristics, so as shown in FIG. It instantaneously becomes larger than _cpA , and then stabilizes at a peak value of 15.734kHz, V _cpB . The point at which the peak value V _cpA momentarily becomes larger is 24kHz and 15.734k.
This is the time when both Hz modes are asynchronous and the horizontal synchronization volume 15 is turned to the position where the horizontal period Th is the largest (see the fluctuation locus P of the collector pulse voltage V _cp shown in FIG. 4).

It is possible to design the horizontal synchronization Th to be extended to a lower frequency side, but if the horizontal period Th is designed to be unnecessarily lower to a lower frequency side, the collector pulse voltage V _cp will increase, as is clear from equation (1) above. Therefore, in order to compensate for this, the power supply voltage variable circuit 4
9, which increases the power consumption and is uneconomical. For this reason, conventionally, the depth of the horizontal frequency Th has been appropriately determined by taking the above-mentioned transient phenomenon into consideration.

(Problems to be solved by the invention) Now, as mentioned above, the horizontal synchronization volume 1
In the non-synchronized state in which the motor 5 is being rotated, if a synchronizing signal is input, there is a suction effect that attempts to synchronize, so the collector pulse voltage V _cp can be relatively small. On the other hand, when the synchronization signal is not input, the above-mentioned suction effect does not exist, so the collector pulse voltage V _cp becomes large. And frequency switching control signal generation circuit 2
At the time when the switching control signal is outputted by 9, that is,
At the moment when the horizontal deflection frequency of the horizontal oscillation time constant variable circuit 11 is switched, the horizontal AFC circuit 51 is set to 24 kHz.
When both horizontal synchronization signals of 15.734kHz are not input, when the horizontal synchronization volume 15 is turned to the position where the horizontal synchronization Th is the largest and the switching control signal is output, the circuit 51 changes to one of the collector pulse voltages V _cp . synchronized action to suction the area is not performed. Therefore, the horizontal output transistor 37 has a large collector pulse voltage generated due to the above transient characteristics.
V _cp is added directly. Therefore, if this collector pulse voltage V _cp is larger than the rated voltage, there is a risk that the horizontal output transistor 37 will be destroyed.

The present invention was created in view of the above points, and an object of the present invention is to provide a horizontal deflection circuit that prevents destruction of the horizontal output transistor of the horizontal output circuit.

(Means for Solving the Problems) FIG. 1 is a block diagram showing the configuration of the present invention.

In FIG. 1, the horizontal oscillation time constant variable circuit 11
includes a time constant setting element, and the switching control of this element generates this threshold voltage at different horizontal deflection frequencies.

The sawtooth voltage is shaped into a pulse signal by a pulse shaping circuit 31. The pulse signal is amplified by the horizontal drive circuit 33.

The horizontal output circuit 35 includes a horizontal output transistor, and supplies a sawtooth current to the deflection yoke upon input of a pulse signal.

The frequency switching control signal generation circuit 29 outputs a switching control signal to the horizontal oscillation time constant variable circuit 11, and switches and controls the time constant setting elements of the circuit 11.

The power supply voltage variable circuit 49 changes the power supply voltage _Vcc upon input of the switching control signal, and steps down or steps up the voltage applied to the horizontal output transistor.

A part of the horizontal output circuit is fed back to the horizontal AFC circuit 51, and the feedback signal is compared with the horizontal synchronization signal to output an AFC voltage to the horizontal oscillation time constant variable circuit 11.

The detection circuit 61 detects whether a horizontal synchronization signal is input to the horizontal AFC circuit 51.

The horizontal deflection frequency switching stop circuit 71 outputs a switching stop signal to the horizontal oscillation time constant variable circuit 11.

(Embodiments of the Invention) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a horizontal deflection circuit according to the present invention,
A horizontal oscillation time constant variable circuit 11 is provided. This horizontal oscillation time constant variable circuit 11 includes a horizontal synchronizing volume 15 and a resistor 1 connected to a power supply element 13.
7. It includes a charging time constant circuit consisting of a time constant setting capacitor 19, and a discharging time constant circuit consisting of the capacitor 19, a resistor 21, and a switching element 23. The capacitor 19 includes a capacitor 25 for varying the time constant and a switching means 27 for switching the time constant.
are connected in parallel. This switching means 27 is a switching transistor 27a.
, a diode 27b connected in parallel to the transistor 27a, and a capacitor 27c for stabilizing switching connected to the base of the transistor 27a. A frequency switching control signal generation circuit 29 is connected to the base of the transistor 27a via resistors 29a and 29b.
Transistor 27a is made conductive by a switching control signal from , and time constant variable capacitor 25 is connected in parallel to time constant setting capacitor 19 .

A which is the output side of the horizontal oscillation time constant variable circuit 11
A pulse shaping circuit 31 and a horizontal drive circuit 33 are connected to the point positions. Pulse shaping circuit 31
pulse-shapes the sawtooth voltage output from the horizontal oscillation time constant variable circuit 11. The horizontal drive circuit 33 amplifies this pulse signal and outputs it to the horizontal output circuit 35. The horizontal output circuit 35 includes a horizontal output transistor 37 to which a pulse signal is input, a damper diode 39 and a retrace condenser 41 connected in parallel between the collector and emitter of the transistor 37, and a scanning capacitor 4.
A deflection yoke 45 is connected via 3.

A power supply voltage variable circuit 49 for horizontal amplitude control is connected to the collector of the horizontal output transistor 37 via an output transistor 47. This power supply voltage variable circuit 49 changes the voltage applied to the collector of the horizontal output transistor 37 from the power supply terminal 13' upon input of the switching control signal.

The horizontal oscillation time constant variable circuit 11 has a horizontal
An AFC circuit 51 is connected. This horizontal AFC
The circuit 51 receives 24kHz or
A 15.734kHz horizontal synchronization signal is input. Also,
A part of the collector pulse voltage V _cp applied to the horizontal output transistor 37 is fed back to the horizontal AFC circuit 51 as a comparison signal.

A detection circuit 6 is provided on the input side of the high-pass filter 53.
1 is connected. This detection circuit 61 includes a high input impedance element 61a and a diode 61.
a rectifier circuit consisting of a capacitor 61c and a switching transistor 61 whose base is connected to a diode 61b via a resistor 61d.
Consists of e. The collector of this transistor 61e is connected to a power supply terminal 61g via a resistor 61f. A transistor 71b is connected to the collector of the transistor 61e via a base resistor 71a. This transistor 71b has its collector connected to the base of the transistor 27a forming the switching means 27 via a resistor 29a, and forms a horizontal deflection frequency switching stop circuit 71.

Next, the operation of the horizontal deflection circuit according to the present invention will be explained.

When the switching control signal is not output from the frequency switching control signal generation circuit 29 and the transistor 27a is open, the time constant variable capacitor 25 is electrically disconnected from the capacitor 19, and when the horizontal oscillation time constant variable circuit 11 The constant becomes smaller. Therefore,
When the capacitor 19 is charged from the power supply terminal 13 via the horizontal synchronization volume 15 and the resistor 17, and the switching element 23 opens and closes at a frequency of 24kHz, the charging current of the capacitor 19 flows to the common side via the resistor 21, so that A A sawtooth voltage is generated at the point with a horizontal deflection frequency of 24kHz.

The sawtooth voltage is shaped into a pulse signal by a pulse shaping circuit 31, amplified by a horizontal drive circuit 33, and then applied to the base of a horizontal output transistor 37 of a horizontal output circuit 35. The horizontal output transistor 37 is thereby closed, so that current flows through the deflection yoke 45. Since the deflection yoke 45 has a large inductance, the current flowing through it gradually increases. Here, when the horizontal output transistor 37 is closed, current flows into the retrace capacitor 41 due to the back electromotive force of the deflection yoke 45, and the current in the deflection yoke 45 decreases. and,
The damper diode 39 is then connected to the deflection yoke 4.
5 and the retrace capacitor 41 to prevent resonance current from flowing. Therefore, the deflection yoke 45 is supplied with a sawtooth current.

On the other hand, the horizontal AFC circuit 51 compares the phase of the 24kHz horizontal synchronization signal and the collector pulse voltage V _cp applied to the horizontal output transistor 37 and outputs the AFC voltage, so the horizontal oscillation time constant variable circuit 11 is stabilized. Repeats the oscillation operation.

In addition, 24kHz or 15.734k is applied to the horizontal AFC circuit 51.
When any Hz horizontal synchronization signal is input, this horizontal synchronization signal is input to the high input impedance element 61a, rectified and smoothed by the diode 61 and capacitor 60c, and then sent to the base of the transistor 61e. and closes the transistor 61e. Therefore, the transistor 7 forming the horizontal deflection frequency switching stop circuit 71
1a is held open.

Now, 24kHz or 15.734k is applied to the horizontal AFC circuit 51.
If any horizontal synchronizing signal of Hz is not inputted, the horizontal synchronizing signal will not be inputted to the detection circuit 61 either, so the transistor 61e is switched to an open state. Therefore, the transistor 71a forming the horizontal deflection frequency switching stop circuit 71 is closed, and its collector is connected to the base of the transistor 27a of the time constant switching switching means 27, so that the switching control signal is The current flows through transistor 71a. Therefore, when the horizontal synchronization signal is not present, the transistor 27a is not closed, and the time constant variable capacitor 25 is connected to the condenser 1.
9 is not connected in parallel. As a result, even if the switching control signal is output, the horizontal oscillation time constant variable circuit 11 outputs a sawtooth voltage at the horizontal deflection frequency of 24 kHz or 15.734 kHz.

Therefore, the power supply voltage V _cc is stepped down by the switching control signal, and the ratio between the horizontal period Th and the retrace period Tr does not change, so as is clear from equation (1) above, the collector pulse voltage V _cp becomes smaller. . Therefore, even when switching from 24kHz to 15.734kHz, the horizontal output transistor 37 has a small collector pulse voltage.
Since only V _cp is added, its destruction can be effectively prevented.

(Effects of the Invention) According to the present invention, when switching the horizontal deflection frequency, it is possible to prevent a large collector pulse voltage from being applied to the horizontal output transistor due to the transient characteristics, so that the horizontal output transistor is not destroyed. Therefore, since it is possible to shorten the horizontal retrace period, it is possible to increase the horizontal deflection frequency and improve the screen resolution.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a horizontal deflection circuit according to the present invention, FIG. 2 is a circuit diagram of a horizontal deflection circuit according to an embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional horizontal deflection circuit. , FIG. 4 is a characteristic diagram showing the collector pulse voltage change when switching the horizontal deflection frequency. 11... Horizontal oscillation time constant variable circuit, 25... Time constant variable capacitor, 27... Time constant switching switching means, 29... Frequency switching control signal generation circuit, 35... Horizontal output circuit, 37... Horizontal Output transistor, 49...Power supply voltage variable circuit, 5
1...Horizontal AFC circuit, 61...Detection circuit, 61
e, 71b...Transistor, 71...Horizontal deflection frequency switching stop circuit.

Claims (1)

[Claims] 1. A variable horizontal oscillation time constant circuit whose time constant setting element is controlled to switch to oscillate at different horizontal deflection frequencies, and a frequency switching control signal generator that supplies a switching control signal to the variable horizontal oscillation time constant circuit. a horizontal output circuit including a horizontal output transistor and outputting a sawtooth current to the horizontal deflection coil in response to an oscillation signal from the horizontal oscillation time constant variable circuit; a horizontal synchronization signal corresponding to the different horizontal deflection frequencies; A frequency control circuit that compares the output fed back from the horizontal output circuit and controls the oscillation operation of the horizontal oscillation time constant variable circuit and a horizontal deflection frequency of the horizontal oscillation time constant variable circuit switches the horizontal output transistor. A horizontal deflection circuit comprising: a power supply voltage variable circuit that changes an applied DC voltage; and a detection circuit that detects non-input of the horizontal synchronizing signal to the frequency control circuit; A horizontal deflection circuit comprising: a horizontal deflection frequency switching stop circuit that stops switching the horizontal deflection frequency of the oscillation time constant variable circuit. 2. The horizontal deflection according to claim 1, wherein the horizontal oscillation time constant variable circuit includes switching means for changing the time constant by switching the time constant setting element upon input of a switching control signal. circuit. 3. The horizontal deflection frequency switching stop circuit according to claim 2, wherein the horizontal deflection frequency switching stop circuit includes switching means for blocking input of a switching control signal to the switching means of the horizontal oscillation time constant variable circuit. Deflection circuit. 4. The horizontal deflection according to claim 1 or 2, wherein the detection circuit includes a rectifier circuit that rectifies the horizontal synchronizing signal, and switching means that operates upon input of the rectified signal. circuit. 5. The horizontal deflection circuit according to claim 1, wherein the detection circuit is connected to the input side of the frequency control circuit to detect non-input of the horizontal synchronization signal. 6. The horizontal deflection circuit according to claims 1 and 2, wherein the frequency control circuit is a horizontal AFC circuit.