JPH0448066Y2 - - Google Patents

Description

[Detailed description of the invention] <Technical field> The present invention is a beam protector malfunction that prevents malfunction of the beam protector circuit that turns off the power supply circuit and protects the circuit elements in color television when beam current flows excessively. Regarding the prevention circuit.

<Prior art> In conventional color televisions, if excessive beam current flows through the secondary side of the flyback transformer, each circuit element including the flyback transformer will malfunction. Some devices are equipped with a beam protector circuit BP as shown in a. In other words, if a beam current of more than a certain value flows through the flyback transformer FBT,
Since the voltage at point E in the figure decreases, diode _D1
becomes conductive, and then the first and second transistors Q ₁ and Q ₂ constituting the beam protector circuit BP are sequentially turned on. Then, the collector voltage of the second transistor _Q2 decreases, so the power supply circuit is turned off with this voltage drop and the flyback transformer is turned off.
I am trying to stop FBT from working.

On the other hand, in a conventional color television, a color control circuit CC for color saturation control as shown in FIG. can be adjusted. In other words, when the resistance value of the color volume VR is increased to increase the voltage at point F in the figure, the color control circuit CC increases the color saturation, and conversely, by decreasing the resistance value of the color volume VR, the voltage at point F is increased. It is configured so that the lower the color saturation, the lower the color saturation.

By the way, depending on the content of the broadcast program, a signal of only one color among R, G, and B may be transmitted. When such a monochromatic color signal is received by a color television with the above configuration, if the resistance value of the color volume VR is set to a large value (that is, the color saturation is large), the cathode current waveform shown in Figure 3 will appear. As shown, the luminance signal component Y increases more than when receiving a color signal that is a mixture of R, G, and B, and the beam current flows beyond a preset value. As a result, the beam protector circuit BP may operate and the power supply circuit may be turned off.

In this way, if the power supply circuit is suddenly turned off in the normal operating state, it is not preferable because it not only makes the reception state unstable, but also creates the illusion that the color television has malfunctioned.

<Purpose of the invention> The present invention was devised in view of the above-mentioned problems, and is intended to prevent malfunctions of the beam protector circuit that occur when the color saturation is set high when receiving monochromatic color signals. The purpose is to effectively prevent.

<Configuration of the invention> The beam protector malfunction prevention circuit of the invention has the following features:
In order to achieve the above purpose, a zener is installed between the beam protector circuit, which turns off the power supply circuit when the beam current exceeds a set value flows to the secondary side of the flyback transformer, and the color control circuit, which controls color saturation. The configuration is such that they are connected via a diode.

<Example> Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

Fig. 1 is a circuit configuration diagram including a beam protector malfunction prevention circuit and its peripheral circuits in a color television showing an embodiment of the present invention, and parts corresponding to the circuit configuration in Fig. 2 are given the same reference numerals. are doing.

The feature of this invention is the flyback transformer FBT.
A Zener diode ZD is connected between the beam protector circuit BP, which turns off the power supply circuit (not shown) when the beam current flows to the secondary side of the The beam protector malfunction prevention circuit ES was constructed by connecting the Note that the Zener voltage of the Zener diode ZD is set by taking into consideration in advance the optimal conditions for turning off the power supply circuit.

In the above configuration, when the color monochromatic signal is received, if the resistance value of the color volume VR is set to a large value, the voltage at point C in FIG. 1 becomes high.
Color saturation has increased. When a color monochromatic signal is received in this state, the luminance signal component Y increases and a beam current of more than a certain value flows through the flyback transformer FBT, causing the voltage at point A in the figure to drop. Then, when the voltage between point A and point B reaches the Zener voltage of Zener diode ZD, this Zener diode ZD becomes conductive, and a current flows between point A and point B. As a result, the voltage at point C also decreases, so the color saturation controlled by the color control circuit CC decreases and an increase in beam current is suppressed. Therefore, even if the color saturation level is set high when receiving a color monochromatic signal, the beam protector circuit will not operate.

Note that if an abnormality occurs in the color television and the beam current flows excessively, the voltage at point E in the figure will further drop, and only then will the beam protector circuit BP operate and turn off the power supply circuit. Become.

<Effects of the invention> As described above, according to the invention, malfunctions of the beam protector circuit that conventionally occur when the color saturation level is set high when receiving monochromatic color signals can be effectively prevented. be able to. This eliminates the inconvenience that occurs when the power supply circuit is turned off in the normal operating state and reception is suddenly interrupted.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram including a beam protector malfunction prevention circuit and its peripheral circuits in a color television showing an embodiment of the present invention; FIG. 2 is a circuit diagram of a beam protector malfunction prevention circuit in a conventional color television; FIG. 3 is a waveform diagram of the cathode current when a color monochromatic signal is received. FIG. 3a shows the case when the color saturation is lowered, and FIG. ES...beam protector malfunction prevention circuit, ZD
... Zener diode, FBT ... flyback transformer, BP ... beam protector circuit, CC
...Color control circuit, VR...Color volume.

Claims (1)

[Scope of utility model registration request] A Zener diode is used to connect the beam protector circuit, which turns off the power supply circuit when the beam current exceeds the set value, to the secondary side of the flyback transformer, and the color control circuit, which controls color saturation. Features a beam protector malfunction prevention circuit for color television.