JPS60145777A - Television receiver - Google Patents

Abstract

PURPOSE:To prevent saturation of the core of a switching transformer and to prevent malfunction of an excess current protection circuit by synchronizing to the timing of channel switching and by lowering the image load by lowering brightness and contrast. CONSTITUTION:The luminance control signal outputted from a terminal 33 is inversed and amplified by resistances 35, 37 and 38, and a transistor 39, and it is smoothed by a resistance 41, a diode 40 and a capacitor 42. The signal becomes the luminance control voltage and is added to a luminance control circuit 17. On the other hand, the contrast control signal outputted from a terminal 34 is inverted and amplified by resistances 43, 45 and 47 and a transistor 46, is smoothed by a resistance 49, a diode 48 and a capacitor 50, and becomes the contrast control voltage. At the time of channel switching, the positive mute pulse which synchronized to channel switching occurs from a terminal 32 of a microcomputer 31, is inverted and amplified by the transistors 39 and 46 through diodes 36 and 44, and lowers the contrast control voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television receiver that performs brightness control and contrast control using a microprocessor such as a microcomputer and is equipped with a switching regulator power supply.

Conventional configurations and their problems In recent years, television receivers have come to have control functions such as brightness control and contrast control using microcomputers, and have come to use switching regulator power supplies.

An example of a conventional television receiver will be described below with reference to the drawings. FIG. 1 shows a block diagram of a conventional television receiver.

In the figure, 1 to 4 are rectifier diodes, and 5 is a smoothing capacitor. 6 is a switching transformer, 7 is a switching control circuit, 8 is an overcurrent protection circuit, 9 is a switching transistor, and 10 is an overcurrent detection resistor.

These 1 to 1o constitute a switching power supply. 11 is a rectifier diode, and 12 is a smoothing capacitor. A predetermined 10B power source is obtained by these. 13 is a synchronization, deflection, and video circuit block. 14 is a cathode ray tube (C
RT). 16 is a channel selection control circuit, 16 is a control microcomputer, and 17 is a tertiary near 7
) roll circuit, 1st is the contrast control circuit. 19 is a television receiver including 1 to 18;

FIG. 2 shows the ABL circuit extracted from the synchronization, deflection, and video circuit block 13 shown in FIG. 21
．． 22.24 is a resistor, 23-digit die shaved, 26 is a capacitor, 26 is a neon tube, 27 is a flyback transformer,
28 is a horizontal output transistor.

Regarding the television receiver configured as above,
The operation will be explained below. First, in Figure 1, diodes 1 to
4 and capacitor 5 rectify and smooth the AC power supply to generate a negative side voltage. Next, j.lance 6 to capacitor 1
A switching regulator power supply configured by 2 supplies 10B power to the secondary side. The 101 B power supply operates the 101 deflection and video circuit 13, and the CRT
The video will be displayed on 14. A video amplification circuit is controlled by a brightness control circuit 17 and a contrast control circuit 18 from among the channel selection control circuit 15.

When the video load becomes large, the collector current of the switching transistor 9 increases, and a voltage above a certain level is generated across the overcurrent detection resistor 1o, which activates the overcurrent protection 8. , stop the switching operation. In FIG. 2, a horizontal output transistor 28 causes a flyback transformer (FBT) 27 to generate high voltage.

In this circuit, when a signal with a low C1 average luminance level (APL) is being received, the beam current is small, so the potential at point a due to the voltage drop across resistor 24 is
．． 22, the diode 23 becomes conductive. Further, the capacitor 26 connected to point a is charged with positive polarity, and the ground side is charged with negative polarity. However, when receiving a signal with a high APL,
Since the beam current is large, the potential at point a due to the voltage drop across resistor 24 is 7L at point b, which is set by resistor 21.22.
The diode 23 is cut off because the voltage becomes lower than the current level. When the diode 23 is cut off, the potential 1-j at point a:
When the APL is low, the AP remains almost constant.
As L becomes higher, it falls. Finally, the potential at point a drops to negative polarity 3, thereby controlling the brightness control circuit 17 and the contrast control circuit 18 to lower the brightness and contrast and reduce the beam current. Capacitor 25 starts discharging at the same time as the potential at point a falls, and a
At the same time that the potential at the point becomes negative, the ground side of the capacitor 5 becomes positive.

However, in the above configuration, when the channel is switched from receiving a low APL signal to a high APL signal, the 11ABL circuit does not operate during the discharge time constant of the capacitor 26, and the beam Excessive current flows.

When a television receiver is used in a high ambient temperature and reduced voltage state, this excessive beam current saturates the core of the switching transformer 6, causing the overcurrent detection circuit 8 to operate and stop the switching regulator operation. There was a problem.

OBJECT OF THE INVENTION The present invention solves the above-mentioned conventional problems, and the switching transformer does not operate even when a signal with a low APL is switched to a signal with a high APL by channel switching in a state where the ambient temperature is high and the voltage is reduced. It is an object of the present invention to provide a television receiver in which the core does not become saturated and, as a result, an overcurrent protection circuit does not operate.

Structure of the Invention The television receiver according to the present invention generates a mute pulse having a time width greater than the time constant of the ABL circuit in synchronization with the timing of channel switching, and applies the mute pulse to the brightness control circuit and the contrast control circuit. At the time of channel switching, the video load is lowered by lowering the brightness and contrast ratio, thereby preventing the core of the switching transformer from becoming saturated, thereby preventing the protection circuit from malfunctioning. This is how it was done.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will now be described with reference to FIG. 3 of the drawings.

FIG. 3 shows a circuit diagram of a contrast control circuit and a degree control circuit in a television receiver according to an embodiment of the present invention. The circuit shown in FIG. 3 is applied to a part of the channel selection control circuit 16 of the television receiver shown in FIG.

In the figure, 31 is a microcomputer for channel selection control, and 32 is a microcomputer that synchronizes with channel switching and
The output terminal of the mute pulse whose time width is 4', '+ is longer than the time constant of the BLl path, and 33 is a PW for brightness control.
The M signal output terminal 34 is a PWM signal output terminal for contrast control. The brightness control signal output from the terminal 33 is inverted and amplified by the resistors 35, 3γ, 3B and the transistor 39, smoothed by the resistor 41, diode 40, and capacitor 42, and is made into a brightness control voltage and applied to the brightness control circuit 1T. On the other hand, the contrast control signal output from the terminal 34 is inverted and amplified by the resistor 43.
and is smoothed by a capacitor 60 to form a contrast control voltage, which is applied to the contrast control circuit 18.

Further, in this circuit, a mute pulse is applied from the terminal 32 to the base of the transistor 390 via the diode 36, and a mute pulse is applied from the terminal 32 to the base of the transistor 460 via the diode 44.

With this configuration, when switching channels, a positive mute pulse with a width greater than the time constant of the ABL circuit synchronized with channel switching is generated from the terminal 32 of the microcomputer 31 for channel selection control, and the diode 36
and 44, and are inverted and amplified by transistors 39 and 46 to reduce the brightness control voltage and contrast control voltage, respectively, to lower the image load.

As a result, under conditions of high ambient temperature and reduced voltage, A
Even when switching from a low PL signal to a high APL signal, the core of the switching transformer 6 will not be saturated during the time constant when the ABLN path does not operate, and the overcurrent protection circuit 8 will not malfunction. be.

Effects of the Invention As described above, according to the present invention, when the ambient temperature is high and the voltage is reduced and the core tolerance of the switching transformer is small, the APL can be changed from a low APL signal by channel switching.
Even when switched to a high PL signal, the core of the switching transformer does not saturate during the time constant when the ABI and circuit do not operate, and the overcurrent protection circuit does not malfunction. It is something that can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional television receiver, FIG. 2 is a circuit diagram of an ABL circuit diagram of the receiver in FIG. 1, and FIG. 3 is a brightness diagram of a television receiver according to an embodiment of the present invention. FIG. 3 is a circuit diagram of a control section and a contrast control section. -6...Converter transformer, 7...Switching control circuit, 8...Overcurrent protection circuit, 9...Switching transistor, 1
3...Synchronization. Deflection, video circuit, 14...Cathode ray tube, 17...
...Brightness control circuit, 18...mark Contrast control circuit jL31...Microcomputer, 32...Mute pulse output terminal, 33.
River: Output terminal for brightness control signal, 34. River: Output terminal for contrast control signal, 36.44.
...Diode, 39.46...Transistor, 40.48...Tiode, 42,6o
・River/Condenser.

Claims (1)

[Claims] A means for controlling the brightness and contrast by a microprocessor, an ABL circuit, and a switching regulator for stabilizing the power supply, and a means for controlling the brightness and contrast by generating a mute halse of the ABL circuit when switching channels. In addition, the television receiver reduces the brightness and contrast when switching channels to prevent excessive beam current from flowing and saturate the core of the switching transformer of the switching regulator.