JPS6260363A - Horizontal deflection circuit - Google Patents

Abstract

PURPOSE:To prevent destruction of a horizontal output transistor (TR) by providing a detection circuit detecting non-input of a horizontal synchronizing signal to a frequency control circuit and a horizontal frequency changeover stopping circuit stopping the changeover of a horizontal deflection frequency of a horizontal oscillation time constant variable circuit with the detection signal. CONSTITUTION:When no horizontal synchronizing signal is inputted to a horizontal AFC circuit 51, since it is not inputted to a detection circuit 51, a TR 61e is switched into non-conductive state. Thus, a TR 71b being a component of the horizontal deflection frequency changeover stop circuit 71 is closed and the collector is connected to the base of the TR 27a of a time constant changeover switching means 27, then a switching control signal is given to the TR 71b. Thus, the TR 27a is not closed and even when the switching control signal is outputted, a horizontal oscillation time constant variable circuit 11 outputs a sawtooth wave voltage. Thus, a power supply voltage VCC is dropped and the ratio of the horizontal period Th to the retrace period Tr is not fluctuated, then a collector pulse voltage VCP is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) 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 horizontal deflection frequency and increase the number of scanning lines 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 between the horizontal period Th and the retrace period Tr is T h /T
r is getting larger.

Incidentally, the collector pulse voltage Vcp of the horizontal output transistor constituting the horizontal output circuit of the horizontal deflection circuit can be expressed by the following equation.

Vcp=Vcc(π/2(Th/Tr-1) +1)・
...(1) However, Vcc indicates the 1TL source voltage of the horizontal output transistor.

As is clear from this equation (1), when the ratio Th/'Tr between the water cycle Th and the retrace period Tr becomes sharp,
Collector pulse voltage Vcp also increases. Therefore, in order to improve the resolution and increase the image output period, it is necessary to reduce the retrace period, and therefore it is necessary to use a transistor with high breakdown voltage characteristics as the horizontal output transistor.

Recently, one display device can also be used as a terminal for computers with different scanning cycles, or as an NTSC display device.
It is also used as a video camera terminal using a signal frequency of 15.734 kHz. And for this purpose, for example, the frequency of the data signal is 24kHz and the NTS
A horizontal deflection circuit that performs horizontal scanning by switching the frequency of the C signal, 15.734 kHz, is required.

FIG. 3 shows a conventional horizontal deflection circuit of this type, which includes a variable horizontal oscillation time constant circuit 11. As shown in FIG. This horizontal oscillation time constant variable circuit 11 includes a charging time constant circuit consisting of a horizontal synchronizing volume 15 connected to a power supply terminal 13, a resistor 17, and a capacitor 19 for setting a time constant;
, a resistor 21, and a discharge time constant circuit including 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. Horizontal drive circuit 33
A horizontal output circuit 35 is connected to the output side of. 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 transformer 47, and the variable circuit 49 changes the voltage applied to the horizontal output transistor 37 from the power supply terminal 13.

Further, the output side of the horizontal oscillation time constant variable circuit 11 has a horizontal A
An FC circuit 51 is connected. This horizontal AFC circuit 5
1 includes a bypass filter 53 for removing vertical synchronization signals, etc.
24kHz2 or 15.734 from input terminal 12 via
A kHz 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, and the time constant of the horizontal oscillation time constant variable circuit 11 becomes small. Therefore, from the power supply terminal 13, the horizontal synchronization volume 15. When the capacitor 19 is charged via the resistor 17, the switching element 23
When the switching operation is performed at a frequency of kHz, the charging current of the capacitor 19 flows to the common side via the resistor 21, so that a sawtooth voltage is generated at the point A at a horizontal deflection frequency of 24 kHz. 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 becomes conductive when a pulse signal is input, and the damper diode 39 becomes conductive depending on the polarity of the voltage charged in the retrace capacitor 41. The deflection yoke 45 has a large inductance. Therefore, the deflection yoke 45 has a frequency of 24kHz.
A sawtooth wave current flows.

On the other hand, the horizontal AFC circuit 51 includes the horizontal output transistor 3.
The collector pulse voltage applied to 7 is fed back. Therefore, this horizontal AFC circuit 51 has 24
The phases of the kHz horizontal synchronization signal and the collector pulse voltage are compared, and the AFC voltage is output to point A, whereby the oscillation frequency of the horizontal oscillation time constant variable circuit 11 is phase-controlled by the horizontal synchronization signal.

Next, a switching control signal is output from the frequency switching control signal generation circuit 29, and when the time constant switching switching means 27 is closed, the capacitor 25 for variable time constant is connected in parallel to the capacitor 19. Therefore, the time constant of the horizontal oscillation time constant variable circuit 11 becomes large. Therefore, when the switching element 23 opens and closes at a frequency of 15.734 kHz, a sawtooth voltage is generated at point A at a horizontal deflection frequency of 15.734 kHz. Therefore, as described above, the deflection yoke 45 is provided with 15
．． A sawtooth current is provided at 734kHz. In addition, since a 15.734 kHz horizontal synchronization signal is input to the horizontal AFC circuit 51, the horizontal oscillation time constant variable circuit 11
is stably phase controlled.

By the way, the horizontal frequency Th is changed from 24 kHz to 15.7
When switching to 34 kE (z), if the retrace period Tr is constant, the collector pulse voltage Vc increases by the amount that the horizontal frequency Th becomes sharper, as is clear from the above equation (1).
p becomes larger. Therefore, it is necessary to reduce the power supply voltage VCC in consideration of the withstand voltage of the water output transistor.

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

Iypr = Vcc (Th-Tr) /L fist
Fist (2) However, L indicates the inductance of the deflection yoke.

Now, when the power supply voltage Vcc is reduced, not only the collector pulse voltage Vcp becomes constant, but also the horizontal amplitude of the screen becomes constant. Furthermore, when the ratio T h /Tr between the horizontal period Th and the retrace period Tr is made constant, as is clear from the above equation (1), the collector pulse voltage Vcp becomes constant as shown in the following equation (3). .

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

Iypr = Vcc (K −1) Tr/L
v * * a (4) In this equation (4), since K is constant, the water frequency Th can be changed from 24kHz to 1
When switching to 5.734kHz, the retrace period Tr
becomes large, so in order to keep the horizontal amplitude of the screen (proportional to I ypr) constant, it is necessary to reduce the power supply voltage Vcc.

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 VCC of the power supply terminal 13' is stepped down by the power supply voltage variable circuit 49, and the horizontal output transistor 37 is I try to add it to. However, at the time when the horizontal frequency is switched from 24 kHz to 15.734 kHz, the collector pulse voltage Vcp becomes 24 kHz as shown in FIG. 4 because the tail source voltage variable circuit 49 has transient characteristics.
It momentarily becomes larger than the peak value VcpA of 15.734kHz, and then stabilizes to the peak value VcpB of 15.734kHz. The point at which the peak value V cpA momentarily becomes larger is when both the 24 kHz and 15.734 kHz modes are asynchronous, and the horizontal synchronization volume 15 is turned to the position where the horizontal period Th becomes the sharpest. It is (
(See the fluctuation trajectory P of the collector pulse voltage Vcp shown in FIG. 4).

It is possible to design the horizontal period Th to be expanded to a lower frequency side, but if the horizontal period Th is designed to be unnecessarily low frequency side, the collector pulse voltage Vcp will increase, as is clear from the above equation (1). In order to correct this, the power consumption of the power supply voltage variable circuit 49 increases, which is uneconomical. For this reason, conventionally, the region of the horizontal frequency Th has been appropriately determined in part by taking into account the above-mentioned transient phenomenon.

(Problems to be Solved by the Invention) As mentioned above, in the asynchronous state in which the horizontal synchronization volume 15 is being rotated, if a synchronization signal is input, there is a suction action that attempts to synchronize. The collector pulse voltage Vcp may be relatively small. On the other hand, when the synchronization signal is not input, the L suction action does not exist, so the collector pulse voltage Vcp becomes large. Then, at the time when the switching control signal is output from the frequency switching control signal generation circuit 29, that is, at the time when the horizontal deflection frequency of the horizontal oscillation time constant variable circuit 11 is switched, the horizontal AFC circuit 51 is supplied with 24kHz and 15.73kHz.
When both horizontal synchronizing signals of 4 kHz are not input, when the horizontal synchronizing volume 15 is turned to the position where the water mole periphery Th is the largest and the switching control signal is output, the circuit 51 converts a part of the collector pulse voltage Vcp. The suction drying does not perform synchronous operation. Therefore, a large collector pulse voltage Vcp generated due to the above transient characteristics is directly applied to the horizontal output transistor 37. Therefore, if this collector pulse voltage Vcp 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 these points, and an object thereof is to provide a horizontal deflection circuit that prevents destruction of the horizontal output transistor of the horizontal output circuit.

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

In FIG. 1, a horizontal oscillation time constant variable circuit 11 includes a time constant setting element, and generates sawtooth voltages at different water moat deflection frequencies by controlling the switching of this element.

The sawtooth voltage is shaped into a pulse signal by a pulse shaping circuit 31. The pulse signal is amplified by the wood motor live circuit 33.

The horizontal output circuit 35 includes a water 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 to switch and control the time constant setting element 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 levitation 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, which includes a variable horizontal oscillation time constant circuit 11. As shown in FIG. This horizontal oscillation time constant variable circuit 11 includes a horizontal synchronizing volume 15 connected to a power supply terminal 13, a resistor 17, and a time constant setting capacitor 1.
A charging time constant circuit consisting of 9, a capacitor 19, and a resistor 2
1, a discharge time constant circuit consisting of 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. This switching means 27 includes a switching transistor 27a and a switching transistor 27a.
It consists of a diode 27b connected in parallel to transistor 7a, and a capacitor 27c for switching stabilization connected to the base of transistor 27a. transistor 27
A frequency switching control signal generation circuit 29 is connected to the base of the circuit a via resistors 29a and 29b, and a switching control signal from this circuit 29 turns on the transistor 27a, and the time constant variable capacitor 25 becomes a time constant setting capacitor. 19
are connected in parallel.

A pulse shaping circuit 31 and a horizontal drive circuit 33 are connected to the A protrusion head which is the output side of the horizontal oscillation time constant variable circuit 11. The 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,
It is output 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 capacitor 41 connected in parallel between the collector and emitter of the transistor 37, and a retrace capacitor 41. A deflection yoke 45 is connected thereto.

A power supply voltage variable circuit 49 for horizontal amplitude control is connected to the collector of the water output transistor 37 via an output transformer 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.

A water flow AFC circuit 51 is connected to a point A of the horizontal oscillation time constant variable circuit 11. A horizontal synchronizing signal of 24 kHz or +f15.734 kHz is input to this horizontal AFC circuit 51 via a bypass filter 53 for removing vertical synchronizing signals and noise. In addition, this horizontal AFC circuit 5
1, a part of the collector pulse voltage VCp applied to the water output transistor 37 is fed back as a comparison signal.

A detection circuit 61 is connected to the input side of the bypass filter 53. This detection circuit 61 includes a high input impedance element 61a, a diode 61b, and a capacitor 61.
a rectifier circuit consisting of a diode 61b and a resistor 61d.
and a switching transistor 61e whose base is connected via a switching transistor 61e. 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 7'la. This transistor 71b has its collector forming the switching means 27 and is connected to the base of the transistor 27a via a resistor 29a, forming 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 z9 and the transistor 27a is open, the variable time constant capacitor 25 is electrically disconnected from the capacitor 19, and when the horizontal oscillation variable time constant circuit 11 The constant becomes smaller. Therefore, the capacitor 19 is charged from the power supply terminal 13 via the horizontal synchronization volume 15 and the resistor 17.
When switching element 23 is opened and closed at a frequency of force < 24 kHz, the charging radio wave of capacitor 19 flows to the common side via resistor 21, so that a sawtooth voltage is generated at point A at a horizontal deflection frequency of 24 kHz.

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. The damper diode 39 is then connected to the deflection yoke 45 and the retrace capacitor 41.
to prevent resonant 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 24 kHz horizontal synchronization signal and the collector pulse voltage Vcp applied to the horizontal output transistor 37 and outputs the AFC voltage, so the horizontal oscillation time constant variable circuit 11 stably oscillates. repeat.

In addition, 24kHz or 15.73kHz is applied to the horizontal AFC circuit 51.
When any of the 4kHz horizontal synchronization signals is input, this horizontal synchronization signal is input to the high input/impedance element 61a, rectified and smoothed by the diode 61b and capacitor 61c, and then connected to the base of the transistor 61e. is added to close the transistor 61e. Therefore, the transistor 7La forming the horizontal deflection frequency switching stop circuit 71 is kept open.

Now, 24kHz or 15.73kHz is applied to the horizontal AFC circuit 51.
If any horizontal synchronizing signal of 4 kHz is not input, the horizontal synchronizing signal will not be input 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 transistor 27a of the time constant switching switching means 27.
Since the transistor 71a is connected to the base of the transistor 71a, the switching control signal flows through the transistor 71a. Therefore, when there is no horizontal synchronizing signal, the transistor 27a is not closed, and the variable time constant capacitor 25 is not connected in parallel to the capacitor 19. As a result, even if the switching control signal is output, the horizontal oscillation time constant variable circuit 11 will not operate at 24kHz or 15kHz.
．． Outputs sawtooth voltage with the horizontal deflection frequency of 734kHz.

Therefore, the power supply voltage Vcc is stepped down by the switching control signal,
Furthermore, since the ratio between the water period Th and the retrace period Tr does not change, the collector pulse voltage Vcp becomes small, as is clear from equation (1) in E.

Therefore, even if the frequency is switched from 24 kHz to 15.734 kHz, only a small collector pulse voltage Vcp is applied to the horizontal output transistor 37, so that 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 reduce the horizontal retrace period, it is possible to increase the horizontal deflection frequency and improve the screen resolution.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a horizontal deflection circuit according to the present invention, FIG. 2 is a circuit configuration diagram of a horizontal deflection circuit according to an embodiment of the present invention, and FIG. 3 is a circuit configuration 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, 51... Horizontal AFC circuit, 61... Detection circuit, 61e, 71b... Transistor, 71... Horizontal deflection frequency switching stop circuit. Patent applicant: Victor Japan Co., Ltd.

Claims (1)

[Claims] 1. A variable horizontal oscillation time constant circuit whose time constant setting element is controlled to switch and oscillate at different horizontal deflection frequencies, and a frequency switching control signal that supplies a switching control signal to the variable horizontal oscillation time constant circuit. It includes a generation circuit and a horizontal output transistor,
a horizontal output circuit that outputs a sawtooth wave current to a horizontal deflection coil using an oscillation signal from the horizontal oscillation time constant variable circuit;
a frequency control circuit that compares a horizontal synchronization signal corresponding to the different horizontal deflection frequencies with an output fed back from the horizontal output circuit, and controls an oscillation operation of the variable horizontal oscillation time constant circuit; A horizontal deflection circuit comprising: a power supply voltage variable circuit that changes a direct current voltage applied to the horizontal output transistor by switching the horizontal deflection frequency of the circuit, the detection detecting non-input of the horizontal synchronization signal to the frequency control circuit; and a horizontal deflection frequency switching stop circuit that stops switching the horizontal deflection frequency of the variable horizontal oscillation time constant circuit in response to a detection signal from the detection circuit. 2. The horizontal oscillation time constant variable circuit according to claim 1, wherein the horizontal oscillation time constant variable circuit includes switching means that changes the time constant by switching the time constant setting element upon input of a switching control signal. Deflection circuit. 3. 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. Horizontal deflection circuit. 4. The horizontal detection circuit according to claim 1 or 2, wherein the detection circuit includes a rectification circuit that rectifies the horizontal synchronization signal, and a switching means that operates on input of the rectification signal. Deflection 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.