JPH0294882A - Brightness adjusting circuit - Google Patents

Abstract

PURPOSE:To obtain the same brightness to any input level by distinguishing a wide aspect signal and an existing broadcast signal and switching a changeover means provided in series with a DC current transmission line deciding the operation of an automatic brightness limiter(ABL) circuit and an automatic contrast limiter(ACL) circuit. CONSTITUTION:In the case of a cathode ray tube 5 offering the wide aspect display, a switch 32 is closed by a control signal sent from a wide aspect signal detector 33 and a current flowing to a return of an FBT 1 depends on the resistance of a resistor 3. Upon the receipt of an existing broadcast signal, the switch 32 is opened by a control signal from the wide aspect ratio signal detector 33. Thus, the current flowing to the return of the FBT 1 depends on the sum of the resistances of the resistors 3, 31 and the operation of the ABL circuit and the ACL circuit receiving much current is limited.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a brightness adjustment circuit in a video circuit used in a television receiver.

(Prior Art) In recent years, with the development of various technologies, a review of broadcasting systems has been proposed. There are methods that achieve wide aspect while maintaining compatibility with current receivers, and methods that are not compatible but significantly improve image quality and achieve wide aspect. However, it is extremely inconvenient to have dedicated receivers for each of them due to current living environment constraints, and it would be very convenient if one receiver could receive images from both the current broadcasting systems.

Most television receivers use cathode ray tubes, but the anode current I11, which determines the overall brightness of the cathode ray tube, cannot be allowed to flow beyond the standard due to performance and life issues. For this reason, when an anode current that exceeds the normal standard flows in a television receiver, an auto brightness limiter (hereinafter referred to as ABL circuit) that changes the black level of the picture and lowers the overall brightness, reduces the cathode transfer width of the picture. The device is equipped with an auto contrast limiter (hereinafter referred to as an ACL circuit) that lowers the brightness to limit the anode current.

In addition, in the case of pulse-like inputs as shown in Fig. 2 (a) and (b), the time-averaged anode current 1.4 is small, so the ABL
The peak auto contrast limiter (hereinafter referred to as peak ACL) is used because the ACL circuit does not work and the transfer width from the cathode becomes too large, causing the phosphor of the cathode ray tube to become saturated and whitewashing, and the anode voltage to drop and blooming to occur.
circuit).

Figure 3 shows the ABL circuit and ACL circuit of current television receivers.
This is an example of a circuit. The high voltage output of the flyback transformer 1 is connected to the anode of the cathode ray tube 5, and the return of the flyback transformer 1 is connected to a DC power source B2 (approximately 100 volts) via a resistor 2 and a resistor 3. This DC power supply +82 is connected to ground via a capacitor 4. The connection point 23 between the resistor 2 and the resistor 3 is N
A PN type buffer 7 is connected to the base of the transistor 7, and is also connected via a diode 6 to a DC power source B3 (approximately 10-odd volts).

Is the collector of the NPN buffer transistor 7 connected to the DC current?
The emitter is connected to ground via a resistor 8.9, and is also connected to a contrast control terminal 27 of a video signal control circuit 22 via a diode 10 and a resistor 11. The video signal control circuit 22 converts the video signal received from the detection circuit 30 into, for example, a Y signal and an R signal.
The signal is decoded into a -Y signal and a B-Y signal, subjected to various video processing, and sent to the cathode of the cathode ray tube 5 via the video output circuit 29. Said con again!・Last control terminal 27 is resistor 1
2 to the sliding end of the contrast adjustment volume 14, and both ends of this volume 14 are connected to a resistor 5, respectively.
It is connected to a constant voltage power supply +83 via a resistor 13 and to ground via a resistor 15.

The connection point 24 between the resistor 8 and the resistor 9 is a diode 16
, are connected to a bright control terminal 28 of a video signal control circuit 22 via a resistor 17, and this terminal 28 is further connected to a sliding end of a bright adjustment volume 20 via a resistor 18. Both ends of the volume 20 are connected to a constant voltage power source 83 via a resistor 19 and to ground via a resistor 21, respectively.

In the brightness adjustment circuit configured as described above, the DC power supply element 8
2, the current flowing through the resistor 3 is approximately constant depending on the voltage obtained by subtracting the voltage drop due to the diode 6 from the potential difference between the DC power supply element 82 and the DC power supply +83, and the resistance value of the resistor 3. This current is assumed to be 18.

When horizontal and vertical signals as shown in Fig. 4 (a) and (b) are input and the average brightness of the entire screen is low, the anode current flowing from the flyback transformer 1 to the cathode ray tube 5 is smaller than la. Therefore, sufficient current flows through the diode 6 and the NPN buffer 7 transistor 7, and the base-emitter voltage VIE of the transistor 7 does not change much due to the current, so the emitter is connected to the DC power supply terminal B.
A voltage close to , appears. Therefore, the resistor 8 is also connected to the connection point 24.
, a contrast control terminal 27 to which a voltage determined by the ratio of the resistor 9 is applied, which is determined by the contrast adjustment volume 14 and the brightness adjustment volume 20;
Since the voltage is higher than that of the bright control terminal 28, the video signal sent to the video output circuit 29 is controlled by the adjustment volume 14.
．． 20. The waveform at the cathode of the cathode ray tube 5 is as shown in FIG. +84 is video output circuit 2
This is the DC power supply voltage of transistor No. 9.

When signals in the horizontal and vertical directions as shown in FIGS. 6(a) and 6(b) are input and the average brightness of the entire screen is high, the anode current flowing from the flyback transformer 1 to the cathode ray tube 5 has a value close to Ia. , the current flowing from the connection point 23 into the diode 6 and the base of the NPN buffer transistor becomes smaller. Therefore, the voltage at the emitter of the transistor 7 and the connection point 24 decreases, and the voltage at the contrast control terminal 27 and bright control terminal 28 is lowered than the voltage determined by the contrast adjustment volume 14 and the flight adjustment volume 20.

As described in 1- below, the average brightness decreases and the anode current 111
to ensure that the standards are not exceeded. The waveform at the cathode of the cathode ray tube 5 is as shown in FIG.

In FIG. 7, ``A'' indicates a case where the ABL circuit and ACL circuit are working, and ``A'' indicates a case where there is no ABL circuit and ACL circuit.

When a television receiver having, for example, a 5:3 wide aspect cathode ray tube as shown in FIG. 8 receives an RF multiplied signal or a video signal of the current broadcasting system, a screen as shown in FIG. 9 is displayed. A is the part where the current broadcasting system is displayed. In other words, changing the horizontal amplitude (-) to limit the horizontal amplitude to only the period l in Figure 9 would complicate the equipment, so it is necessary to shorten the video time of the 4=3 aspect during the period l. During periods m and n, a mask signal or the like is used to cut off the video output transistor of the video output circuit so that the screen becomes black.

Therefore, when a wide aspect signal is received and when a current broadcast signal is received, the waveforms transferred to the cathode are as shown in FIG. 10 and FIG. 11, respectively. When the input signal amplitude 111 is small as shown in FIGS. 10(a) and 11(a), the cathode transfer amplitude 11+ of both signals does not change, and the brightness of the portion where the image is present does not change.

As shown in Figures 10 (b) and 11 (b), if the input signal amplitude 1 [1 is large (when using the current ABL circuit or ACL circuit), the current broadcasting signal When a wide aspect signal is received, the black level is higher and the contrast is higher than when a wide aspect signal is received.

When various video signals are input, the contrast is suppressed in the video in which the peak ACL circuit operates, so an increase in the black level is visually observed, and the signal of the small amplitude 111 becomes brighter. Images in which the peak ACL circuit does not operate will have a whitish appearance, and viewers will have to adjust the brightness with the brightness adjustment volume, contrast adjustment volume, etc. when receiving a wide aspect signal or when receiving a current broadcast signal. It is inconvenient to have to make adjustments.

Furthermore, when a picture with a large amount of white is received, the beam is concentrated in the center, so that the shadow mask is more likely to deform than when a wide aspect signal is received, causing color unevenness.

(Problems to be Solved by the Invention) As mentioned above, if a wide aspect receiver is configured with conventional ABL circuits and ACL circuits, the black level and contrast will change when receiving wide aspect signals and current broadcasting. There was a problem. Therefore, the present invention is intended to eliminate the above-mentioned problems, and allows the same brightness to be obtained with any level of human effort, whether the entire CRT is used to project an image or only a portion of the CRT is used. The purpose is to provide a brightness:A adjustment circuit.

[Structure of the Invention] (Means for Solving the Problems) The present invention includes a discriminating means capable of discriminating between a wide aspect signal and a current broadcasting signal and outputting a discriminating signal, and an ABL circuit that can be opened and closed by the discriminating signal. It consists of a switching means provided in series with a direct current transmission line that determines the function of the ACL circuit, and a resistor connected to both ends of this switching means.

(Function) In the present invention, the switching means opens when receiving a current broadcast,
The direct current that determines the operation of the ABL and ACL circuits is limited by a resistor, and even if the display screen becomes smaller, the ABL and ACL circuits operate with the same brightness as if they were larger, so the brightness is the same for all input levels. can be obtained.

(Example) The present invention will be described below based on the example shown in the drawings.

FIG. 1 is a circuit diagram showing a brightness adjustment circuit according to an embodiment of the present invention. In FIG. 1, the same parts as in FIG. 3 are given the same reference numerals and explained.

In Fig. 1, the high voltage output of the flyback transformer 1 is connected to the anode of the cathode ray tube 5, and the return of the flyback transformer 1 is connected to a DC power supply +82 (for example, 150V) via resistors 2, 31, and 3. It is connected. This DC power supply +8. is connected to ground via a capacitor 4. The resistor 31 is provided with a switching device such as a switch 32 for shorting and opening! This switch 32 is controlled by a control signal from a control signal generating circuit, such as a wide aspect signal detector 33. Connection point 2 between resistor 31 and switch 32
3 is connected to the base of the NPN buffer transistor 7, and is also connected to the DC power supply +83 (
For example, it is connected to 12V).

The collector of the NPN buffer transistor 7 is connected to the DC power supply +83, and the emitter is connected to the resistor 8.9.
is connected to ground via a diode 10,
It is connected to a contrast control terminal 27 of a video signal control circuit 22 via a resistor 11. This video signal control circuit 22 receives the video signal from the detection circuit 30, for example,
The signal is decoded into a R-Y signal and a B-Y signal, subjected to various video processing, and sent to the cathode of the cathode ray tube 5 via the video output circuit 29. Further, the contrast control terminal 27 is connected to the sliding end of the contrast adjustment volume 14 via the resistor 12, and both ends of the volume 14 are connected to the constant voltage power supply element 83 via the resistor 13 and to the ground via the resistor 15, respectively. It is connected to the.

The connection point 24 between the resistor 8 and the resistor 9 is a diode 16,
It is connected to the bright control terminal 28 of the video signal control circuit 22 via the resistor 17, and this terminal 28 is further connected to the resistor 1.
8 to the sliding end of the brightness adjustment volume 20. Both ends of the brightness adjustment volume 20 are connected to a constant voltage power source B3 via a resistor 19 and to ground via a resistor 21, respectively.

Next, the operation of the brightness adjustment circuit will be explained. That is,
The current flowing from the DC power supply element B2 to the cathode of the diode 6, the resistor 2, and the NPN buffer transistor 7 is equal to the voltage obtained by subtracting the voltage drop across the diode 6 from the potential difference between +82 and +83, and the value of the resistor 3 or , is determined by the total value of resistor 3 and resistor 31, and is constant when the state of switch 32 is constant.

When the cathode ray tube 5 is performing wide aspect display, the switch 32 is closed by the control signal sent from the wide aspect signal detector 33, and the current flowing into the return of the flyback transformer 1 is determined by the value of the resistor 3, The current flowing into the anode of the cathode ray tube 5 is made not to exceed the standard value of the cathode ray tube 5.

Let this value be Ia.

When a current broadcast signal is received, the switch 32 is opened by a control signal from the wide aspect signal detector 33. Therefore, the current flowing into the return of flyback transformer 1 is determined by the total value of resistor 3 and resistor 31, and if more current tries to flow, the ABL circuit,
ACL circuit works and limits. Now, if the screen area ratio of the wide aspect signal and the current broadcasting signal is 5=4, in order to operate the ABL circuit and ACL circuit so as to obtain the same brightness per unit area, the anode current of the cathode ray tube during current broadcasting must be 415) Ia. Therefore, resistor 3
The value of 1 may be set to approximately 0.25 times the value of resistor 3.

FIGS. 10(e) and 11(c) show the case where the input signal amplitude is large (the ABL circuit according to the present invention, the AC
[Effects of the Invention] As described above, according to the present invention, even if the size of the display screen changes, the same unit can be used for all input signal levels. The brightness per area can be kept constant, and there is no need to perform any brightness adjustment or contrast adjustment when switching display screens. In other words, the same brightness can be obtained with any level of human effort whether an image is projected using the entire cathode ray tube or a portion thereof, and a natural-looking image can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a pulse-shaped input waveform with a large amplitude and a display screen that operates a conventional peak ACL circuit, and FIG. 3 is a diagram showing a conventional peak ACL circuit. Circuit diagrams showing examples of brightness adjustment circuits, Figures 4, 5, and 6.
Figure 7 is a diagram explaining the circuit operation of the conventional ABL circuit and ACL circuit, respectively. Figure 8 is a perspective view showing a wide aspect cathode ray tube. Figure 9 is a screen using wide aspect signals and the display of the current broadcasting system. Diagram showing the screen, 1st
0 is a cathode waveform diagram when a wide aspect signal is received by a wide aspect cathode ray tube, and FIG. 11 is a cathode waveform diagram when a current broadcasting signal is received by a wide aspect cathode ray tube. 1...Flyback transformer, 5...Brown shield'
, 7...NPN type buffer transistor, 14...
Contrast adjustment volume, 20... Brightness adjustment volume, 22... Video signal control circuit, 27...
Contrast control terminal, 28...Bright control terminal,
29... Video output circuit, 30... Detection circuit, 31...
-Resistor, 32...Switch, 33...Wide aspect signal detector. Applicant's agent Patent attorney Suzue Takehiko (a) (1)) Artist (a) Mizuhikata Nyo (b) Takata v Fig. Fig. Fig. Fig. Δ Fig. Fig. Wide adversary Toshi issue No. 1゜ Diagram of the number of transmission issues

Claims (1)

[Claims] In a brightness adjustment circuit in a circuit used in a television receiver, one end is connected to a first DC power supply via a resistor, and the other end is connected to a voltage from the first DC power supply via a diode. A first resistor connected to a second DC power supply with a low current and a return terminal of the flyback transformer via a resistor, and a short-circuit, open-circuit 1. A brightness adjustment circuit comprising: a switching device for controlling the switching device; and a control signal generating circuit for generating a signal for controlling the switching device.