JPH0537579Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of a color television (hereinafter also referred to as "TV") receiver.

[Conventional technology]

When the power to a color TV receiver is turned off, a bright spot shines on the CRT (cathode ray tube), which is the display device, or a
Sometimes the book becomes a bright line and shines (hereinafter this development will be referred to as the "CRT spot phenomenon"). Due to such development, an electron beam exceeding the rating of the CRT is concentrated on a part of the phosphor, causing damage to the phosphor. As a result, when the power is turned on again, the damaged phosphor will no longer emit light even when a regular electron beam is projected on it, causing damage to the image.

By reducing the occurrence of such CRT spot phenomenon,
Regarding the countermeasures taken in conventional color TV receivers to protect CRTs from damage.
This will be explained with reference to FIG. Figure 2 shows a color signal output circuit 3, which is a part of the circuit of a color TV receiver, and a CRT 4 that displays the reproduced color signal.
A spot phenomenon reduction circuit (hereinafter also simply referred to as a "reduction circuit") 5 that reduces the CRT spot phenomenon is shown. Terminal In ₁ is a color signal regeneration circuit (not shown)
An input terminal for the color difference signal (RY signal) obtained in
Similarly, terminals In ₂ and In ₃ are input terminals for the G-Y signal and the BY signal, respectively. Each color difference signal is applied to the bases of color signal output NPN transistors Q ₁ , Q ₂ , Q ₃ via current limiting resistors R ₁ , R ₂ , R _{3 ,} respectively. R ₄ , R ₅ , R ₆ are transistors Q ₁ , Q ₂ , Q ₃ respectively
load resistance, R ₇ , R ₈ , R ₉ are each transistor
These are the emitter resistances of Q ₁ , Q ₂ , and Q ₃ . Also, Vcc
is a constant power supply for the color signal output circuit 3, _C1 is a smoothing capacitor for suppressing the voltage fluctuation of the constant power supply, and terminal _In4 is the R-Y, G-Y, B-Y color difference signal. , G, and B color signals. The −Y signal supplied from the input terminal In ₄ is connected to the resistors R ₁₀ and
It is applied to the emitters of transistors Q ₁ , Q ₂ and Q ₃ via R ₁₁ and R ₁₂ , respectively. As a result, R, G, and B amplified by transistors Q ₁ , Q ₂ , and Q ₃
The respective color signals are applied to the cathode electrode of the CRT 4 through current limiting resistors R ₁₃ , R ₁₄ , and R ₁₅ , respectively.
It is played as a video screen.

On the other hand, the reduction circuit 5 includes a polar capacitor C ₂ ,
It consists of a resistor R ₁₆ and a diode D ₁ . Capacitor C ₂ and resistor R ₁₆ are internal DC power supply (hereinafter also simply referred to as "power supply") Vcc - ground (earth)
The + side of the capacitor _C2 is connected to the power supply Vcc, the - side is connected to the ground via the diode _D1 (connected in the forward direction), and is also connected to the first grid _g1 of the CRT4. . In such a configuration, when the power switch of the color TV receiver is closed (0N) and the screen is displayed, the power is turned off.
Since a bias is applied to the anode side of diode D ₁ from Vcc through resistor R ₁₆ , diode D ₁ is conductive (ON), and this diode D ₁
The voltage of the first grid g ₁ connected to the anode of the diode D 1 becomes the saturation voltage (offset voltage) V _D of the diode D ₁ . Further, a constant voltage Vc is applied to both ends of the capacitor _C2 , and the capacitor C2 operates in a stable state.

Next, the conditions for CRT4 to emit light are as follows:
A high voltage (20-odd KV) is applied to the anode of 4,
6.3V voltage to CRT heater (neither shown),
The CRT heater is heated by a current of several hundred mA, a voltage of several hundred V is applied to the screen (second grid) _g2 , and a voltage _VD close to ground potential is applied to the first grid _g1 . With a voltage of several tens to hundreds of volts applied to the cathode, after fixing the screen voltage and first grid voltage to certain values, the cathode voltage is set to a certain value (supposed to be ν ₁ V). The CRT 4 will not emit light at a voltage higher than that. Also,
Below ν ₁ V, the emission intensity of the CRT 4 changes depending on the voltage value, and the lower the voltage, the greater the emission intensity.
On the other hand, when the cathode potential is constant and the screen voltage is changed by changing the first grid voltage, the relationship is such that the higher the voltage is raised, the more the emission intensity increases. Therefore, the reason why the CRT emits light in dots or in a single line immediately after the power switch on the receiver is turned off (opened) is because the dots emit light while the CRT's light emission conditions are met. This occurs when both the horizontal and vertical polarization circuits of the receiver stop working, and the case of linear light emission occurs when either the horizontal or vertical polarization circuit of the receiver stops working.

In order to reduce this CRT spot phenomenon, conventional color TV receivers are equipped with a reduction circuit 5 shown in the second figure.
was supported. Its operation is as follows. In other words, the power switch on the receiver body is opened (OFF).
As a result, the voltage of the power supply Vcc of the color output circuit 3 naturally decreases with a certain time function. Since the color output circuit 3 is connected to the first grid _g1 through the capacitor _C2 , a current i flows through the circuit of the capacitor _C2 and the resistor _R16 in response to a voltage drop in the power supply Vcc.
As a result, the diode _D1 becomes non-conductive, and the first grid _g1 is biased to the negative side, which makes it difficult for the CRT to emit light compared to when it is fixed to ground (potential 0). This is what we are using.

[The problem that the idea attempts to solve]

In order to increase the effectiveness of the reduction circuitry of such conventional devices, it is necessary to reduce the voltage of the power supply Vcc more rapidly. However, when the voltage of the power supply Vcc decreases, the collector voltages of the color output transistors _Q1 to _Q3 also decrease, which in turn means that the cathode potential of the CRT 4 decreases. Therefore, the CRT4 will have a stronger emission intensity, which is contradictory due to the relationship between the cathode and the first grid _g1.Due to the constraints from the emission conditions of the CRT4, no improvement beyond a certain level can be expected, and the CRT spot The drawback was that the phenomenon could not be completely eliminated.

[Means to solve the problem]

The present invention provides a color TV receiver equipped with at least a color signal output circuit and horizontal and vertical blanking circuits, which includes a capacitor charged by a DC power supply for the horizontal and vertical blanking circuits during power input operation, and a DC power supply. means for electrically disconnecting the capacitor from the DC power supply due to a voltage drop in the capacitor;
A spot phenomenon removal circuit having at least a resistor that cooperates with the capacitor to set its discharge time constant to a desired value is provided, and after the power to the receiver body is turned off, the charge stored in the capacitor is removed from the spot. The above problem has been solved by arranging that the color signal is supplied to the color signal output transistor of the color signal output circuit through the switching means of the phenomenon removal circuit and the horizontal and vertical blanking circuits.

〔Example〕

An embodiment of the color television receiver of the present invention will be described with reference to FIG. 1st
The figure is a circuit diagram of the main parts of the color television receiver 1 of the present invention, including a luminance signal amplification circuit 6 (block display only), horizontal and vertical blanking circuits 7, and a circuit for eliminating CRT spot phenomenon. A spot phenomenon removal circuit (hereinafter also simply referred to as "removal circuit") 8 is illustrated. In this figure, the same components as those in FIG. 2 are denoted by the same reference numerals, and detailed explanation thereof will be omitted. Also, in Figure 1,
Illustrations of CRTs, etc. are also omitted.

Next, the operation will be explained. The output of the luminance signal amplification circuit 6 is supplied to the base of the buffer transistor _Q4 . Terminal In ₅ is a blanking input terminal from which horizontal blanking pulses and vertical blanking pulses are supplied to the base of NPN transistor Q ₇ . Since the blanking pulse BP has a level higher than the offset voltage V _BE of the transistor _Q7 , the transistor _Q7 conducts (ON) every time the blanking pulse BP enters, and the resistor _R22 (PNP transistor Q 1 of ₈ bias resistors
ground). This allows transistor Q ₈
It also conducts. Here, if the saturation voltage of the transistor Q ₈ is V _CES8 and the voltage of the power supply Vcc is V _CC , then the collector voltage of the transistor Q ₈ is V _CC −V _CES8 .
R ₂₃ is the collector resistance of transistor Q ₈ , and since the collector of transistor Q ₈ is connected to the base of blanking transistor Q ₅ , the period during which blanking pulse BP exceeds the offset voltage V _BE of transistor Q ₇ has transistor Q ₅
becomes conductive and transistor _Q4 becomes non-conductive. Therefore, the common emitter resistance R ₂₄ of transistors Q ₄ and Q ₅
Assuming that the offset voltage of transistor _Q5 is _VBE5 , a potential difference of V _CC -V _CES8 -V _BE5 will occur across the terminals of the transistor Q5.

While the blanking pulse BP does not exceed the offset voltage _VBE of the transistor _Q7 , the voltage across the resistor _R24 is Vy- _VBE4 ( _VBE4 : the offset voltage of the transistor _Q4 , Vy: the output of the brightness signal amplification circuit 6). voltage is applied. The connection point between resistor R ₂₄ and both transistors Q ₄ and Q ₅ is connected to the base of PNP transistor Q ₆ , whose collector is grounded and whose emitter is connected to the resistor.
Connected to power supply Vcc via _R25 . moreover,
The connection point between the emitter of the transistor _Q6 and the resistor _R25 is connected to the input terminal _In4 , and is supplied with the -Y signal.

The above is an explanation of the main structure and normal display operation of the color TV receiver 1 of the present invention. Next, the operation for removing the CRT spot phenomenon will be explained. The main cause of the CRT spot phenomenon that occurs when the power to the receiver is turned off is that the CRT cathode voltage drops earlier than the voltage applied to the other electrodes of the CRT. One reason for this is that, as mentioned above, the power supply Vcc shown in the second diagram drops first. This point can be solved by increasing the capacitance of capacitor _C1 . Another cause is when the voltage of the color difference signal supplied to the bases of the color output transistors _Q1 to _Q3 falls slower than the voltage of the luminance signal -Y supplied to each emitter, or This is a case where there is a specific peak.

Such a case will be described using the transistor _Q1 , which is one of the color output transistors, as an example, with reference to FIGS. 3 to 5. 3 to 5 are characteristic diagrams showing fluctuations in the base voltage and emitter voltage of the transistor _Q1 when the power is turned off. That is, in FIG. 3, and FIGS. 4 and 5,
The relationships between base and emitter voltage fluctuations are shown when the CRT spot phenomenon does not occur and when it does occur, respectively. As shown in the third figure, when the base voltage becomes lower voltage faster than the emitter voltage, the CRT spot phenomenon does not occur, but the fourth
If the base voltage remains higher as shown in the figure, or
As shown in FIG. 5, if the base voltage becomes higher in the middle, a CRT spot phenomenon occurs. In particular, in the case of voltage fluctuations as shown in Figure 5, the emitter voltage of transistor Q ₁ becomes higher than the base voltage immediately after the power switch of the receiver body is turned off, and transistor Q ₁ becomes non-conducting. Therefore, the collector or cathode potential of the transistor _Q1 is approximately equal to the power supply voltage of the color signal output circuit 3, and the CRT beam does not flow. Therefore, the CRT anode voltage has not decreased much either. By the way, at time t ₁ after the power is turned off, the emitter voltage and the base voltage have the same value, and at the next time t ₂ , the base voltage becomes higher than the emitter voltage, making the transistor Q ₁ conductive. in this case,
If the deflection circuit has already become inoperable after the power is turned off and before time _t2 , the period _t2 to _t3 during which the base voltage is higher than the emitter voltage by more than the offset voltage _VBE of transistor _Q1 . and intense
CRT spot phenomenon occurs.

In the color television receiver of the present invention, the occurrence of such a phenomenon is eliminated by providing a removal circuit 8, and the configuration and operation of the removal circuit 8 will be explained below with reference to FIG. 3 and subsequent figures. . The removal circuit 8 is a PNP transistor Q ₉ ,
It consists of diodes _D2 to _D4 , resistors _R26 to _R28 , and capacitor _C3 , and is constructed by connecting these as shown in the first figure. During normal display operation of a color TV receiver, the internal DC power supply Vcc is at a predetermined positive voltage.
V _CC is maintained, and transistor Q ₉ is non-conducting (OFF) because its base is connected to power supply V CC through resistor R ₂₆ and is reverse biased.
Also, capacitor _C3 is a forward connected diode
It is connected to the power supply Vcc through _D4 , and the voltage across capacitor _C3 increases the saturation voltage of diode _D4 to V _D4.
Then, it becomes V _CC −V _D4 .

Here, when the power switch of the receiver is turned off, the voltage of the power supply Vcc is changed to the capacitor C ₁ (see Figure 2).
Attenuates as the discharge occurs. If the offset voltage of transistor _Q9 is _VBE9 , the voltage of power supply Vcc is
When the voltage drops below V _CC −V _D4 −V _BE9 , transistor Q ₉ becomes conductive. On the other hand, the diode _D4 is cut off by reverse bias, and the electric charge charged in the capacitor _C3 is discharged through the transistor _Q9 and the resistor _R27 . Further, the collector of the transistor _Q9 is connected to the base of the transistor _Q5 via a diode _D2 , and is also connected to the emitter of the transistor _Q6 via a diode _D3 and a resistor _R28 . In this state diode _D4 is non-conducting;
Most of the charge on capacitor C ₃ is transferred to transistor Q ₉
The emitter flows through the collector. The discharge time constant determined by the capacitance of capacitor C ₃ and the resistance value of resistor R ₂₇ is set to be sufficiently larger than the voltage drop time constant of power supply Vcc, so that even after the voltage of power supply Vcc decreases, the charge of capacitor C ₃ is maintained. Diode D ₂ and
It can be supplied via D ₃ to the base of transistor Q ₅ and the emitter of transistor Q ₆ , respectively. By supplying the charge to the transistor _Q5 , the charge of the capacitor _C3 is also supplied to the luminance signal amplification circuit 6.

Now, when there is no voltage applied to the base of transistor _Q5 via diode _D2 , the base voltage of transistor _Q4 decreases as the voltage of power supply Vcc decreases. Therefore, the emitter voltage of transistor _Q4 and the base voltage of transistor _Q6 also decrease. As a result, even if the charge of capacitor C _{3 is supplied to the emitter of transistor Q 6 via} diode D ₃ and resistor R ₂₈ , since transistor Q ₆ is forward biased, the emitter voltage of transistor Q ₆ is The voltage drops almost the same as the voltage drop of the internal DC power supply Vcc. Therefore, in order to avoid this, a voltage is supplied to the base of the blanking transistor Q ₅ via the diode D ₂ to make the transistor Q ₄ non-conductive. Here, the transistor
If the collector voltage of Q ₉ is V _9t , then the transistor
The emitter voltage of Q ₅ , that is, the base voltage of transistor Q ₆ is V _9t −V _D2 −V _BE5 . If the current flowing through the resistor R ₂₈ is i ₃ , the emitter voltage of the transistor Q ₆ is V _9t −V _D3 −R ₂₈ i ₃ , and the following formula: V _9t −V _D3 −R ₂₈ i ₃ −(V _9t −V _D2 -V _BE5 ) <V _BE6 By selecting the value of resistor _R28 , transistor _Q6 becomes non-conductive.

Therefore, the emitter voltage of transistor Q ₆ (V _9t −
V _D3 −R ₂₈ i ₃ ) to the luminance signal input terminal In ₄ in Figure 2.
Transistor via resistors R ₁₀ , R ₁₁ , R ₁₂
When supplied to the emitters of Q ₁ , Q ₂ , and R ₃ , the result (this example is only for transistor Q ₁ , but the same applies to transistors Q ₂ and Q ₃ ) is as shown by the broken line in Figure 5. , even between time t ₂ and _{t 3} after the power supply Vcc is turned off, the base voltage of transistor Q ₁ remains constant.
It is possible to set it so that it does not exceed the emitter voltage of _Q1 . As a result, in the color television receiver of this invention, when the power is turned off, the CRT
It is possible to completely prevent the occurrence of the spot phenomenon, and it is possible to prevent damage to the CRT's phosphor due to electron beams exceeding the rating, which occurred when the power was turned off in conventional color television receivers. It is possible to eliminate scratches on the displayed image.

〔effect〕

Since the color television receiver of the present invention is configured as described above, it is possible to completely prevent the occurrence of the CRT spot phenomenon when the power is turned off, and it is possible to completely prevent the CRT spotting phenomenon that occurs when the power is turned off in conventional color television receivers. It is possible to prevent damage to the CRT phosphor caused by the electron beam as described above, and it is possible to eliminate damage to the displayed image when the power is turned on again. In addition, the residual charge of the capacitor is supplied to constant voltage horizontal and vertical blanking circuits, etc., instead of the horizontal and vertical deflection circuits that require high voltages, as seen in, for example, Japanese Utility Model Application Publication No. 57-182973. A small capacitor with low withstand voltage characteristics is sufficient, and since a sufficiently long time constant can be set with this capacitor C ₃ and resistor R ₂₇ , the capacitance of the spot killer can be set sufficiently long, etc. Has practical features.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit configuration diagrams of the main parts of the color television receiver of the present invention and the conventional color television receiver, respectively, and Figures 3 to 5 show variations in the base voltage and emitter voltage of the color output transistor when the power is turned off. It is a characteristic diagram showing the situation. 4...CRT, 6...Brightness signal amplification circuit, 7...
...Horizontal and vertical blanking circuits, 8...Spot phenomenon removal circuits, _C1 to _C3 ...Capacitors, _D1 to _D4
...Diode, Q ₁ to Q ₉ ...Transistor, R ₁
~R ₂₈ ...Resistor, Vcc...Internal DC power supply.

Claims (1)

[Claim for Utility Model Registration] A color television receiver equipped with at least a color signal output circuit and horizontal and vertical blanking circuits, which is charged by a DC power source for the horizontal and vertical blanking circuits during power input operation. a capacitor, a means for electrically disconnecting the capacitor from the DC power supply due to a voltage drop in the DC power supply, a switch means operating by being brought into continuity by the electrical disconnection, and a switch means that cooperates with the capacitor to discharge the capacitor. A spot phenomenon eliminating circuit having at least a resistor for setting a time constant to a desired value is provided, and after the power to the receiver body is cut off, the electric charge stored in the capacitor is transferred to the spot phenomenon eliminating circuit and the spot phenomenon eliminating circuit. A color television receiver characterized in that the color signal is supplied to the color signal output transistor of the color signal output circuit through horizontal and vertical blanking circuits.