JPS6127245Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in horizontal hold-down circuits for television receivers.

It is well known that in general television receivers, when the high output voltage rises abnormally, X-rays are generated from the picture tube. Therefore, a horizontal hold-down circuit is used to stop the operation of the horizontal output circuit in such cases, but most conventional hold-down circuits detect a rise in the high-voltage output voltage as a rise in the power supply voltage. I was doing it.

However, an increase in high output voltage is caused not only by an increase in the power supply voltage but also by destruction or deterioration of the resonant capacitor in the horizontal output circuit, so the above method for detecting a rise in power supply voltage does not detect the increase in high voltage caused by this resonant capacitor. cannot be dealt with.

In addition, in order to eliminate the drawbacks of such a method of detecting power supply voltage, a tertiary winding for detection is provided in the flyback transformer in the horizontal output circuit, and as the output voltage of this tertiary winding increases, high voltage is generated. Horizontal hold-down circuits that detect increases in output voltage have also been proposed.

However, even with this method of detecting the voltage rise of the tertiary winding, the relationship between the high voltage output voltage of the flyback transformer and the output voltage of the tertiary winding is different when the power supply voltage rises and when the capacitance of the resonant capacitor changes. It's on. That is, FIG. 2 shows the high voltage output voltage V _h and the output voltage of the tertiary winding V _d in case A when the power supply voltage increases and case B when the capacitance of the resonant capacitor changes.
Each represents the relationship between As can be seen from this figure, even if the hold-down operation is set to a certain fixed tertiary winding detection voltage V _dp ,
In the case of straight lines A and B, the hold-down operation will not start at the same high output voltage value. This means that, for example, assuming that X-rays are generated when V _h > V _h1 , the hold-down operation will be performed normally in case A, but in case B, V _h = V _h2 . Otherwise, the hold-down operation will not be performed, and conversely, when V _h > V _h2 ,
Assuming that X-rays are generated, the hold-down operation will be performed normally in case B, but in case A, the hold-down operation will be performed at V _h = V _h1 , where X-rays are not generated. .

Furthermore, the high-voltage output voltage also changes depending on the picture tube beam current, and the generation of X-rays is not simply related to the magnitude of the high-voltage output voltage V _h but also to the magnitude of the beam current I _b at that time. There is. That is, curve A in FIG. 3 indicates the boundary line of the X-ray generation area,
Curve B shows the actual I _b - V _h characteristic of the receiver, and when detecting a rise in the high output voltage with the tertiary winding as described above, the hold-down characteristic is It becomes approximately constant as shown by straight line C in the figure. Therefore, when designing a hold-down circuit, it is necessary to ensure that the straight line C does not intersect with the curves A and B, but this means that the design is extremely difficult. This is because straight line C has an intersection with curve A, which means that hold-down operation is not performed in a normal region, and having an intersection with curve B means that the generation of X-rays is a region where X-ray generation is not a problem. This is because the hold-down operation will be started due to a change in the beam current.

Therefore, the present invention proposes a horizontal hold-down circuit that eliminates these drawbacks of the conventional example, and its details will be explained below.

Figure 1 shows an embodiment of the hold-down circuit of the present invention, where 1 is a horizontal oscillation circuit, 2 is a horizontal drive transistor, 3 is a horizontal output transistor, 4 is a horizontal deflection circuit, 5 is a flyback transformer, and 6 is for detection. Transistor 7 is a switching transistor, and this circuit basically produces a DC voltage obtained by rectifying and smoothing the pulse voltage obtained at the tertiary winding 5c of the flyback transformer 5 using a diode _D5 and a capacitor _C5 . V _d is applied to the base of the detection transistor 6 through the resistors R ₁₂ and R ₁₃ , and when this transistor is turned on by the increase in the voltage V _d , the switching transistor 7 is turned on, thereby By supplying a positive voltage to the horizontal drive transistor 2 through its base resistor R ₁ and diode D ₁ , the horizontal drive transistor 2 is saturated and the operation of the horizontal output transistor 3 is stopped. The power supply voltage + _B1 is divided by the voltage dividing resistors _R7 and _R9 and applied to the emitter of the detection transistor 6 via the resistor R8, and the flyback transformer ₅ is applied to the emitter of the detection transistor 6.
The connection point a between the low potential side of the secondary winding 5b for high voltage and the series circuit consisting of a Zener diode Z ₂ for automatic brightness limiting, a diode D ₃ and a resistor R ₁₄ is connected to a diode D ₂ and a resistor R ₁₀ , R This point is connected to the emitter of the transistor 6 through ₁₁ series-parallel circuits.

In addition, D ₄ is a diode for reverse bias protection between the base and emitter of transistor 6, C ₄ is a capacitor to prevent this transistor 6 from malfunctioning due to noise, etc., and R ₁₅ is a screen voltage extraction It is a variable resistor for

In a horizontal hold-down circuit with such a configuration,
Now, for example, the resonant capacitor of horizontal deflection circuit 4
If one or both of C ₁ and C ₂ is destroyed or deteriorated and its capacity decreases, the width of the horizontal blanking period decreases, and as is well known, the high voltage output voltage V of the secondary winding 5b of the flyback transformer 5. _h increases, and at this time, the DC output voltage V _d from the tertiary winding 5c of the flyback transformer 5 also increases, but this increase in V _d is based on straight line B in FIG. V
_d exceeds V _dp which is higher than the emitter potential of the detection transistor 6 by V _BE when V _h becomes more than V _h2 , and this transistor 6 is turned on and held as described above. A down operation is performed. On the other hand, when the power supply voltage +B ₁ increases, the high-voltage output voltage V _h naturally increases, but at this time, the emitter potential of the detection transistor 6 increases in accordance with the increase in the power supply voltage +B ₁ , so V _h = The detection transistor 6 does not turn on even when the voltage reaches V _h1 , and turns on only when V _h reaches V _h2 or more. Therefore, in this case, it means that straight line A corresponds equivalently to straight line A', that is, straight line B. This means that the hold-down operation starts at a certain high output voltage, that is, V _h2 , whether due to a decrease in the capacitance of the resonant capacitor or due to an increase in the power supply voltage.

This operation is performed when the high voltage output voltage V _h increases regardless of the beam current I _b , but as mentioned above, in reality, when I _b changes, I _b - V _h
The characteristics and X-ray generation characteristics change. By the way, a
The voltage at the point changes according to _Ib , and since the Zener diode _Z2 , diode _D3 , etc. are connected there, the voltage changes as shown in FIG.
Therefore, as mentioned above, diode D ₂ and resistor R ₁₀ ,
When R ₁₁ is connected, when the Zener diode Z ₂ and diode D ₃ are off, the diode D ₂ is turned on, and the voltage change ΔV _E of the emitter voltage of the detection transistor 6 at this time is Assuming the voltage change at point a as ΔV _a , ΔV _E =(ΔV _a −V _Z −V _D )×R ₈ +R ₉ /R ₁₀ +R
₈ +R ₉ However, V _Z is the Zener voltage of Zener diode Z ₁ , V _D is the forward rising voltage of diode D ₂ , and when Zener diode Z ₂ and diode D ₃ are on, diode D ₂ is off. Then, ΔV _E at this time is ΔV _E =(ΔV _a -V _Z )×R ₈ +R ₉ /R ₁₁ +R ₁₀
+R ₈ +R _9. Therefore, if the values of resistors R ₁₀ and R ₁₁ are appropriately selected, even if ΔV _a changes in a polygonal manner as shown in FIG. This means that it is possible to transmit a voltage ΔV _E that decreases approximately linearly as the beam current I _b increases. and,
The fact that ΔV _E is transmitted in this way means that the value of the tertiary winding output voltage V _dp that turns on the detection transistor 6, that is, the high voltage output voltage V _h2, changes as shown by the curve C' in FIG. means, therefore, this curve
Since C' is less likely to intersect with curves A and B, hold-down operation is always achieved in a stable region.

Note that if the Zener diode Z ₂ and diode D ₃ for automatic brightness limitation are not connected to point a, the voltage change ΔV a at point _a is equal to the beam current I _b
In this case, it is not necessary to provide the diode _D2 and turn it on and off, since it changes approximately linearly with respect to the change in .

As described above, the horizontal hold-down circuit of the present invention has a detection transistor that detects a rise in the output voltage of the tertiary winding of a flyback transformer, and a voltage that changes in response to a rise in power supply voltage and an increase in the picture tube beam current. A voltage that changes according to the voltage is applied to offset the output voltage of the tertiary winding, thereby correcting the detection operation of the detection transistor according to the fluctuations in the power supply voltage and the beam current. Therefore, it is possible to perform a hold-down operation faithfully to changes in the high-voltage output voltage and always stable, which is effective.

Furthermore, in a preferred embodiment of the present invention, since the voltage that changes in accordance with the increase in the beam current is created by correcting the voltage for automatic brightness limiting, the influence of the operation of the automatic brightness limiting circuit without receiving
Another advantage is that the voltage can be created relatively easily.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the horizontal hold-down circuit of the present invention, and FIGS. 2 to 4 are characteristic diagrams for explaining its operation. 6...Detection transistor, 5c...Tertiary winding of flyback transformer, _R7 , _R9 , _R10 , _R11 ...
…Voltage dividing resistor, D ₂ …Switching diode,
Z ₂ , D ₃ . . . Zener diode and diode for automatic brightness limiting, 2 . . . horizontal drive transistor.

Claims (1)

[Claims for Utility Model Registration] (1) A DC voltage obtained by rectifying and smoothing the output pulse of the tertiary winding of a flyback transformer is applied to the base of a detection transistor, and at the same time, the emitter of this transistor is subjected to fluctuations in the power supply voltage. A voltage that changes in the same direction as the voltage change in response to a change in the voltage and a voltage taken out from the low potential end of the high voltage secondary winding of the flyback transformer in the same direction as the beam current change in response to a change in the picture tube beam current. A horizontal hold-down circuit that applies varying voltages and stops the operation of the horizontal output circuit by turning on the detection transistor. (2) The voltage that changes according to changes in the picture tube beam current is a voltage for automatic brightness limiting, and this voltage connects a switching diode that turns on and off depending on the magnitude of this voltage, and a switching diode connected in series with this diode. and a resistor connected in parallel to the connection point between the emitter of the detection transistor and the resistor connected to the emitter.
Horizontal hold-down circuit as described in section.