JPH0415672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brightness adjustment control voltage generation circuit that generates a brightness adjustment control voltage and supplies it to a brightness adjustment circuit in order to adjust brightness.

FIG. 1 shows a conventional image receiving device including a control voltage generating circuit for brightness adjustment. In FIG. 1, a brightness signal Y is supplied to a brightness adjustment circuit 1. In FIG. The brightness adjustment circuit 1 is configured to, for example, receive a brightness adjustment control voltage and amplify the brightness signal Y including the DC component while controlling the base voltage of the amplification transistor using the brightness adjustment control voltage. There is. The output of the brightness adjustment circuit 1 is amplified by a video amplification circuit 2 having a DC amplification circuit configuration and then supplied to the base of a common collector transistor _Q1 . Power supply +B ₂ is connected to the emitter of transistor Q ₁ through resistor R ₁ .
is supplied. The emitter output of this transistor Q ₁ is the transistor Q ₂ , volume VR ₁ ,
A color difference signal G-Y output from a color demodulator (not shown) in an output amplifier 3 consisting of resistors R ₂ to R ₄
mixed with. At the same time, the emitter output of transistor _Q1 is also supplied to each of output amplifiers 4 and 5, which are configured similarly to output amplifier 3, and mixed with each of the color difference signals R-Y and B-Y. Each of the primary color signals of G, R, and B is outputted from each of these output amplifiers 3, 4, and 5 and applied to each cathode of the picture tube 6. Note that G, R, and B indicate green, red, and blue signals, respectively.

On the other hand, the brightness adjustment control voltage supplied to the brightness adjustment circuit 1 is output from the brightness adjustment control voltage generation circuit 7. Brightness adjustment control voltage generation circuit 7
is the resistor R ₅ connected in series between the power supply +B ₂ and ground,
Volume VR ₂ , R ₆ , a diode D ₁ whose cathode is connected to the slider of the volume VR ₂ , and a diode D whose anode is connected to the cathode of the diode D ₁ and whose cathode is connected to the anode of the diode D ₁ . ₂ and a capacitor C ₁ connected between the anode of the diode D ₁ and ground,
The configuration is such that the voltage derived to the slider of the volume VR ₂ is output as a control voltage for brightness adjustment. In addition, the slider of volume VR ₂ is connected to ABL through diode D ₃ and resistor R ₇ connected in the forward direction.
(automatic brightness limit) circuit (not shown), and when the brightness of the picture tube 6 becomes too bright above a certain level, the volume is adjusted by the action of the ABL circuit.
The voltage drawn to the slider of VR ₂ is now suppressed. The video amplifying circuit 2 also uses blanking pulses output from horizontal and vertical output circuits (not shown) during the retrace period to prevent the electron beam of the picture tube 6 from being emitted during the retrace period. It is configured to include an erase circuit.

The power supply + _B2 is a DC power supply obtained by rectifying the pulse voltage generated in the low voltage winding _L2 of the flyback transformer T by a diode _D4 and smoothing it by a capacitor _C2 . A main power supply + _B1 is supplied to one end of the primary winding L1 of the transformer _T , and the other end of the winding _L1 is connected to the collector of the horizontal output transistor _Q3 . The emitter of transistor _Q3 is grounded, and its base is supplied with a pulse synchronized with the horizontal synchronizing pulse. A damper diode D ₅ and a capacitor C ₃ are connected in parallel between the collector of the transistor Q ₃ and the ground, and a deflection coil L ₃ and a capacitor D ₄ are connected in series. Transistor Q ₃ and diode D ₅ perform a switching operation in response to the pulse supplied to the base of transistor Q ₃ , thereby supplying horizontal deflection current to deflection coil L ₃ , and also supplying horizontal deflection current to transistor Q ₃ during the retrace period. A pulse voltage V _P as shown in the following equation is generated at the collector.

V _P =+B ₁ {(π/2)·(t _S /t _R )+1})... (1) Here, t _S indicates the horizontal scanning period, and t _R indicates the horizontal retrace period.

This voltage V _P is rectified by a diode D ₆ and then smoothed by a capacitor C ₅ and applied to the resistor of the volume VR ₃ . This volume
The voltage derived from the slider of VR ₃ is applied to the screen grid of the picture tube 6 as a screen voltage. Incidentally, a smoothing capacitor _C6 is connected between the slider of the volume _VR3 and the ground.

In addition, the high voltage winding L ₄ of the flyback transformer T
The voltage generated across the voltage is rectified by the diode _D7 , smoothed by the capacitor _C7 , and applied to one end of the resistor of the volume _VR4 .
There is a resistor between the other end of the resistor of volume VR ₄ and ground.
_R8 is connected, and the voltage derived from the slider of the volume _VR4 is applied to the focusing electrode of the picture tube 6 as a focus voltage. Further, a voltage approximately equal to the sum of the voltages generated across each of the high voltage windings L ₄ and L ₅ of the flyback transformer T is rectified by a diode D ₈ and a direct current is applied to the anode of the picture tube 6. The voltage is high.

Note that the collector of the transistor Q ₂ in the output amplifier 3 is supplied with a power supply +B ₃ via a resistor R ₃ , but this power supply +B ₃ is also connected to a low voltage (not shown) of the flyback transformer T, similar to the power supply +B ₂ . It is obtained from the voltage generated across the winding.

In the above configuration, the brightness adjustment circuit 1, the video amplification circuit 2, the transistor Q ₁ , the output amplifiers 3, 4,
Since each of 5 has a DC amplifier circuit configuration,
When the brightness adjustment control voltage supplied to the base of the amplification transistor in the brightness adjustment circuit 1 changes, the cathode voltage of the picture tube 6 changes, and the amount of beam current changes accordingly, so that brightness is adjusted. Ru. Now, when the main power supply +B ₁ is turned on, the voltage of the power supply +B ₂ momentarily becomes abnormally high, but as the voltage of this power supply +B ₂ increases, the voltage drawn to the slider of the volume VR ₂ When the voltage rises, a charging current is supplied to the capacitor _C1 via the diode _D2 to charge the capacitor _C1 , and the rise of the control voltage for brightness adjustment becomes slow. Therefore, the brightness adjustment control voltage does not become abnormally high, and the brightness is prevented from becoming abnormally high. Then, when the power supply +B ₂ changes from a transient state to a steady state, the charging voltage of the capacitor C ₁ becomes equal to a voltage approximately 0.4 V lower than the control voltage for brightness adjustment, and both diodes D ₁ and D ₂ turn off.
Next, when the main power supply +B ₁ is cut off and the voltage of the power supply +B ₁ begins to decrease, the voltage of the power supply +B ₂ also begins to decrease, so the control voltage for brightness adjustment also begins to decrease. Then, when the brightness adjustment control voltage becomes lower than the charging voltage of the capacitor _C1 , the diode _D1 is turned on, and the rate of decrease of the brightness adjustment control voltage is rapidly slowed down by the charging voltage of the capacitor _C1 . That is, the control voltage for brightness adjustment rapidly decreases to a value approximately 0.4V lower than the charging voltage of the capacitor _C1 , and then gradually decreases. As a result, _the rate of decrease in the beam current of the picture tube 6 is suddenly slowed down by turning on the diode _D1 , and the high voltage supply voltage is rapidly reduced. Since the voltage of the power supply + _B2 is accelerated, the positive feedback becomes strong and the image disappears instantly. Therefore, the occurrence of inconveniences such as abnormal images appearing when the main power supply + _B1 is shut off can be prevented.

However, in a TV receiver equipped with a conventional brightness adjustment control voltage generation circuit, even if the voltage of the power supply +B ₁ drops momentarily, the voltage of the power supply +B ₂ instantly drops due to positive feedback. An inconvenience occurs in that the image momentarily disappears every time the voltage of ₁ decreases. It is possible to prevent the occurrence of such problems by stabilizing the power supply + _B2 , but it is preferable to adopt such a method because the stabilization circuit usually has a large number of parts and is expensive to manufacture. do not have.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a brightness adjustment device that has a simple configuration, can erase an image almost instantly when the power is cut off, and can prevent the image from disappearing when the voltage of the power supply drops momentarily. An object of the present invention is to provide a control voltage generation circuit.

The control voltage generation circuit for brightness adjustment according to the present invention includes:
Voltage dividing means for dividing the power supply voltage at a predetermined voltage division ratio;
and a power storage means that is charged by the output voltage of the voltage dividing means so that the charging voltage becomes a predetermined voltage lower than the output voltage of the voltage dividing means, and when the charging voltage becomes higher than the output voltage of the voltage dividing means. This charging voltage is output as a control voltage for brightness adjustment via a resistor.

Hereinafter, the present invention will be explained in detail with reference to FIG.

As shown in FIG. 2, a brightness adjustment circuit 1, a video amplification circuit 2, output amplifiers 3, 4, 5, a picture tube 6, a control voltage generation circuit for brightness adjustment 7, a transistor _Q1 ,
Q ₃ , diodes D ₃ to D ₈ , capacitors C ₂ to D ₇ , volumes VR ₃ and VR ₄ , transformer T, horizontal deflection coil L ₃ and resistors R ₁ , R ₇ and R ₈ are connected in the same way as in Figure 1. has been done. However, in this example, a diode is used in the brightness adjustment control voltage generation circuit 7.
D ₁ , D ₂ , capacitor C ₁ , volume VR ₂ , resistor
R ₅ and R ₆ are connected in the same way as in FIG. 1, but a resistor R ₉ is connected between the cathode of the diode D ₁ and the slider of the volume VR ₂ which is the output end.

In this configuration, when the main power supply +B ₁ is turned on, the capacitor C ₁ is charged in the same way as in the circuit shown in FIG. Since the voltage does not become abnormally high, the brightness is prevented from becoming abnormally high. Also, when the power supply +B ₂ changes from a transient state to a steady state, the charging voltage of the capacitor C ₁ becomes equal to a voltage approximately 0.4 V lower than the control voltage for brightness adjustment, and the diode D ₁ , Both D ₂ are turned off. Next, when the power supply +B ₁ is cut off and the voltage of the power supply +B ₁ begins to decrease, the control voltage for brightness adjustment begins to decrease and becomes lower than the charging voltage of the capacitor C ₁ , as in the circuit shown in Figure 1, and the diode D ₁ turns on.
Then capacitor _C1 starts to discharge, but
Since the discharge current of the capacitor _C1 is limited by the resistor _R9 , the positive feedback effect that promotes the voltage drop of the power supply + _B2 is limited. Therefore, power +
When the voltage of B ₁ momentarily drops, it is possible to limit the increase in the rate of decline of power supply +B ₂ due to the positive feedback effect, which eliminates the problem that the image disappears momentarily every time the voltage of power supply +B ₁ drops. This means that the occurrence can be prevented.

In this example, the resistance value of resistor _R9 is 10KΩ±
It has been experimentally confirmed that the best results are obtained by setting it in the 5KΩ range. resistance
If the resistance value of resistor _R9 is smaller than the above range, sufficient effect will not be obtained, and if the resistance value of resistor _R9 is larger than the above range, it will take a long time for the image to disappear when the power is turned off. A new problem occurs in that an abnormal image such as a return line appears.

As is unusual, the control voltage generation circuit for brightness adjustment according to the present invention has a configuration in which a resistor R ₉ is connected in series with a diode D ₁ that is turned on when the power is turned off and a discharge current of the capacitor C ₁ flows. ,
It is possible to prevent the appearance of an abnormal image by causing the image to disappear almost instantly when the power is turned off, and it is also possible to prevent the image from disappearing instantaneously when the voltage of the power source drops momentarily. In addition, the control voltage generation circuit for brightness adjustment according to the present invention has a relatively simple configuration in which one resistor is added to the conventional circuit, so that a high-performance receiver can be obtained while suppressing an increase in manufacturing costs. We can also expect the effect of being able to do so.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing a part of a television receiver including a conventional brightness adjustment control voltage generation circuit, and FIG.
The figure is a circuit block diagram showing one embodiment of the present invention. Explanation of symbols of main parts, 1... Brightness adjustment circuit,
2... Video amplification circuit, 3, 4, 5... Output amplifier, 6... Picture tube, 7... Control voltage generation circuit for brightness adjustment, Q ₁ , Q ₃ ... Transistor, D ₃ , D ₄ ,
_D5 , _D6 , _D7 , _D8 ...Diode, _C2 , _C3 , _C4 ,
_C5 , _C6 , _C7 ...Capacitor, _VR3 , _VR4 ...Volume, T...Transformer, _L3 ...Horizontal deflection coil, _R1 , _R7 , _R8 ...Resistor.

Claims (1)

[Claims] 1 Voltage dividing means that divides the power supply voltage generated by the flyback transformer that generates the voltage applied to the anode of the picture tube at a predetermined voltage division ratio, and a charging voltage that is charged by the output voltage of the voltage dividing means. is set to be a predetermined voltage lower than the output voltage of the voltage dividing means; and the voltage storage means is turned on when the output voltage of the voltage dividing means drops to a voltage lower than the charging voltage of the power storage means by a predetermined value or more. switch means for relaying the charging voltage to the output terminal of the voltage dividing means, and outputting the voltage derived to the output terminal of the voltage dividing means as a brightness adjustment control voltage for adjusting the brightness of the picture tube. 1. A control voltage generation circuit for brightness adjustment, comprising a resistor connected between the switching means and the output terminal of the voltage dividing means.