JPH0526854Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a circuit that stabilizes high voltage in a monitor to which horizontal synchronizing signals of various frequencies are input, and in particular relates to a circuit that stabilizes high voltage in a high voltage stabilization control section. This invention relates to an overheat prevention high-voltage voltage stabilization circuit that prevents overheating due to heat generated by the vehicle.

(Prior Art) A conventional high voltage stabilizing circuit will be explained with reference to FIG. A horizontal oscillation section 2, a horizontal drive section 3, and a horizontal output section 4 are connected in series to a horizontal synchronization signal terminal 1. One end of the primary coil of the flyback transformer FBT ₁ and a boost up circuit 5 are connected to the horizontal output section 4, respectively. A power source B ₀ ⁺ is connected to the other end of the primary coil. One end of the secondary coil of the flyback transformer _FBT1 is connected to the high voltage terminal H/V through a diode.
The cathode of the diode is grounded through the internal resistance of the flyback transformer FBT ₁ and the external resistance R ₀ . A midpoint between the internal resistance and the external resistance is connected to a boost up circuit 5 via an amplifier section 6.

The operation of the high voltage stabilizing circuit configured in this way will be explained.

The power source B ₀ ⁺ is supplied to the primary coil of the flyback transformer FBT ₁ . The horizontal synchronizing signal applied to the horizontal synchronizing signal terminal 1 undergoes self-oscillation in the horizontal oscillating section 2, and then is applied to the horizontal output section 4 via the horizontal driving section 3. Therefore, the flyback transformer
A large impulse voltage generated by turning on and off the horizontal output transistor in the horizontal output section 4 is released to the secondary coil of the FBT ₁ , and a constant high voltage is output to the high voltage end HV.

At this time, when a horizontal synchronizing signal having a higher frequency than the signal applied to the horizontal synchronizing signal end 1 earlier is input to the signal end 1, the voltage at the high voltage end HV becomes low. This lowers the voltage at point (a). Therefore, in the amplifier section 6, in order to amplify this lowered voltage and deepen the bias of the transistor in the boost up section 5, the collector pulse of the horizontal output transistor in the horizontal output section 4 is made higher to increase the voltage. Stabilize the voltage. Furthermore, when a horizontal synchronizing signal having a higher frequency than that described above is input to the horizontal synchronizing signal terminal 1, the voltage at point (A) decreases more than that described above. In this case,
The amplifier section 6 and the boost up circuit 5 further increase the collector voltage of the horizontal output transistor and apply it to the flyback transformer _FBT1 . This results in
The high voltage on the secondary side of the transformer FBT ₁ becomes stable.

(Problem to be solved by the invention) As is clear from the above description, the difference in the bias of the boost-up transistor becomes significantly large due to the difference in the frequency of the horizontal synchronization signal applied to the horizontal synchronization signal end 1. Become. Therefore, there was a problem that the boost-up transistor overheated.

That is, conventionally, when horizontal synchronizing signals of various frequencies are input, the bias difference between the boost-up transistors becomes extremely large, resulting in the transistors generating considerable heat. Therefore, there is a problem in that the reliability of the boost-up transistor is reduced. Moreover, in order to solve this problem, it is sufficient to increase the area of the heat sink. However, in this case, various new problems arise, such as the overall size of the product.

The present invention attempts to solve the above-mentioned problems by changing the voltage of the power supply supplied to the primary coil of the flyback transformer in accordance with changes in the frequency of the horizontal synchronizing signal, thereby increasing the voltage at the secondary coil of the transformer. It is possible to stabilize the high-voltage voltage of , improve the high-voltage stability with changes in frequency, and prevent overheating of the transistor by reducing the bias change of the boost-up transistor. The purpose is to provide an integrated circuit.

(Example) An example of the present invention will be described with reference to FIG.
A horizontal oscillation section 8 and a horizontal drive section 9 are connected to the horizontal synchronization signal end 7.
and the horizontal output section 13 are sequentially connected in series.
One end of the primary coil of the flyback transformer FBT ₂ and the boost up circuit 14 are connected via the horizontal output section 13. Above flyback transformer
One end of the secondary coil of FBT ₂ is grounded, and the other end is connected to the high voltage end HV through a diode.
The cathode of that diode is connected to the internal resistance and external resistance.
Grounded via _R11 . The middle point (point (a)) between the internal resistance and the external resistance is connected to the boost up circuit 14 via the amplifier section 15.
On the other hand, a frequency change detector 10 is connected to the output end of the horizontal oscillation section 8. A resistor R ₆ of the power switching circuit 11 is connected to one output terminal O ₀₁ of this detector 10.
is connected to the base of transistor _Q4 with its emitter grounded through. The collector of this transistor _Q4 is connected to the bias resistor _R4 and the base of the transistor _Q3 via a resistor _R5 . Further, the other output terminal O ₀₂ of the frequency change detector 10 is connected to the base of a common emitter transistor Q ₂ via a resistor R ₃ of the power switching circuit 12.
The collector of this transistor _Q2 is connected to the bias resistor _R1 and _the base of the transistor _Q1 via a resistor R2.

Furthermore, the power supply B ₃ ⁺ is connected to the emitter of transistor Q ₁ . A power supply B ₂ ⁺ is connected through a diode D ₂ to the midpoint between the collector of the transistor Q ₁ and the emitter of the transistor Q ₃ .
Power supply B ₁ ⁺ through diode D ₁ transistor Q ₃
It is connected to the midpoint between the emitter and the primary coil of flyback transformer FBT ₂ .

The operation of the circuit of the above embodiment configured in this manner will be explained.

First, it is assumed that the magnitude relationship between the voltage of the power supply and the frequency of the horizontal synchronizing signal used in the above embodiment is as follows. That is, the frequency of the horizontal synchronization signal is A(KHz)<
There is a relationship of B (KHz) < C (KHz) < D (KHz),
It is assumed that the power supply voltage has a relationship of B ₁ ⁺ (V) < B ₂ ⁺ (V) < B ₃ ⁺ (V).

When a horizontal synchronization signal of A (KHz) is applied to the horizontal synchronization signal terminal 7, the horizontal oscillation section 8 supplies a horizontal deflection pulse to the horizontal output section 13 via the horizontal drive section 9 to the base of the horizontal output transistor _Q5 . Since the base voltage of the transistor _Q6 in the boost up circuit 14 is constant, the horizontal output section 13 outputs a horizontal pulse from the collector of the horizontal output transistor _Q5 . Two output terminals Q ₁ and Q ₂ of the frequency change detector 10 connected to the output terminal of the horizontal oscillation section 8 each output an L level signal. As a result, transistors Q ₄ and Q ₂ of power switching circuits 11 and 12 are in an off state. Therefore, transistors Q ₃ and Q ₁ are also each in an off state.

Therefore, only the power supply B ₁ ⁺ is supplied to the primary coil of the flyback transformer FBT ₂ , and a constant voltage is maintained at the high voltage end by turning on and off the transistor Q ₅ in the horizontal output section 13. Output to HV.

At this time, when a horizontal frequency of B (KHz) is applied to the horizontal synchronizing signal terminal 7, the frequency change detector 10
One output terminal _O1 outputs an H level signal, and the other output terminal _O2 outputs an L level signal. Since the output terminal O ₂ outputs an L level signal, the transistors Q ₂ and Q ₁ of the power switching circuit 12 maintain the off state. However, the output end O ₁
Since the transistors Q 4 and Q 3 of the power switching circuit 11 are sequentially turned on, the transistors Q ₄ and Q ₃ of the power supply switching circuit 11 are turned on. Turning on transistor Q ₃ connects power supply B ₂ ⁺ , which has a higher voltage than power supply B ₁ ⁺ , to transformer FBT ₂ . That is, when the frequency of the horizontal synchronizing signal changes from the low frequency A (KHz) to the high frequency B (KHz) as described above, the flyback transformer FBT ₂
Although a drop in the high voltage of the high voltage end HV on the secondary side of HV occurs, a power source B ₂ ⁺ higher than the power source B ₁ ⁺ is supplied to the primary side of the flyback transformer FBT ₂ through the transistor Q ₃ of the power switching circuit 11. . Therefore, a constant high voltage is continuously output at the high voltage end HV.

On the other hand, when a horizontal synchronization signal with a frequency of C (KHz) higher than B (KHz) is input to the horizontal synchronization signal terminal 7, both output terminals O ₁ and O ₂ of the frequency change detector 10
Both output H level signals. As a result, the transistors of each power switching circuit 11, 12
Q ₄ , Q ₃ , Q ₂ , and Q ₁ are turned on in substantially the same manner as above. Therefore, the power supply B ₃ ⁺ is a transistor
It is supplied to flyback transformer FBT ₂ through Q ₁ and Q ₃ . Since the power supply B ₃ ⁺ has a higher voltage than the power supplies B ₁ ⁺ and B ₂ ⁺ , at the high voltage end HV, even though the frequency of the input signal to the horizontal synchronization signal input terminal 7 changes high, the high voltage remains constant. Output voltage.

Furthermore, when a signal with a frequency of D (KHz) higher than C (KHz) is input to the horizontal synchronization signal terminal 7, the two output terminals O ₁ and O ₂ of the frequency change detector 10 become H.
Maintain the level and do not change. Therefore, the power switching circuits 11 and 12 continue to operate, and power B ₃ ⁺ is supplied to the flyback transformer FBT ₂ . Therefore, the high voltage at the high voltage end HV decreases. Therefore, the potential at point (a) also decreases at the same time. Therefore, the voltage applied to the negative input terminal of the operational amplifier _OP1 constituting the differential amplifier in the amplifier section 15 also decreases. Since the reference voltage V _ref is applied to the +input terminal of the operational amplifier, a signal obtained by inverting and amplifying the difference between the two input signals is sent to the operational amplifier OP ₁ .
is output from the output terminal. The output increases the base potential of transistor _Q6 in the boost up circuit 14 at the next stage. Therefore, this transistor Q ₆ is grounded, and the emitter of the transistor Q ₅ in the horizontal output section 13 is also grounded. As a result, the maximum value P-P of the collector voltage of the horizontal output transistor _Q5 increases, and the flyback transformer
The high voltage on the secondary side of FBT ₂ is stabilized.

As described above, according to the embodiment of the present invention, it is possible not only to improve the high voltage stability against changes in the frequency of the input horizontal synchronizing signal, but also to actively respond to minute changes in the high voltage due to the screen condition. The high voltage can be quickly stabilized, and a stable high voltage can always be output regardless of changes in the frequency or brightness of the playback screen.
Moreover, overheating of the boost-up transistor is also eliminated as the bias change of the transistor is reduced, which is effective in preventing overheating.

[Effect of idea]

According to the present invention, as the frequency of the horizontal synchronizing signal applied to the horizontal synchronizing signal end increases, a power supply voltage that increases step by step is applied to the primary side of the flyback transformer, so that the frequency of the horizontal synchronizing signal increases. Even if the frequency increases, the output voltage on the secondary side of the flyback transformer can be stabilized, and when the frequency of the horizontal synchronizing signal becomes higher, the increase in frequency is detected as a voltage drop on the secondary side of the flyback transformer. Then, the switching element in the boost up circuit is turned on, and one end of the primary side of the flyback transformer is grounded.
Even in such a case, the output on the secondary side of the flyback transformer can be stabilized, and overheating of the switching element in the boost up circuit can be prevented. Furthermore, although low, medium, and high voltage power supplies are connected to the primary side of the flyback transformer, these three power supply potentials can be selected in advance as arbitrary values, which allows the flyback transformer to Stability on the output side can be made more reliable. Furthermore, if the frequency of the horizontal synchronizing signal increases further after applying the high-voltage power supply to the primary side of the flyback transformer as described above, this can be amplified by amplifying the output of the secondary side of the flyback transformer as a feedback signal. Since the primary side of the flyback transformer is grounded via the switching element in the boost up circuit, the increase in the frequency of the horizontal synchronization signal can be applied to low voltage, medium voltage, and high voltage. Even when the range of stabilization by the power supply is exceeded, the stabilization can be ensured, and the output of the flyback transformer can be stabilized over a wide frequency range of the horizontal synchronizing signal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional high voltage stabilizing circuit. 1, 7...Horizontal synchronization signal end, 2, 8...Horizontal oscillation section, 3, 4...Horizontal drive section, 4, 13...Horizontal output section, 5, 14...Boost up circuit, 6,
15...Amplification unit, 10...Frequency change detector, 1
1, 12...Power switching circuit, B ₀ ⁺ ~ B ₃ ⁺
...Power supply, _D1 to _D3 ...Diode, _Q1 to _Q6 ...
Transistor, R ₁ ~ R ₆ ... Resistor, FBT ₁ , FBT ₂
...Flyback transformer.

Claims (1)

[Claims for Utility Model Registration] One end of the primary side of the flyback transformer FBT2 is connected to the first switching element Q in the horizontal output section 13.
5 and the second switching element Q6 in the boost up circuit 14, and the control terminal of the first switching element Q5 is connected to the horizontal synchronizing signal terminal via the horizontal drive section a and the horizontal oscillation section 8. A low voltage power source B1 ⁺ , a medium voltage power source B2 ⁺ and a high voltage power source B3 ⁺ are connected in parallel to the other end of the primary side of the flyback transformer FBT2, and the low voltage power source B1 ⁺ is directly connected to the other end of the primary side of the flyback transformer FBT2, the medium voltage power source B2 ⁺ is connected to the other end via the first switching circuit 11, and the high voltage power source B3 ⁺ is connected to the other end of the primary side of the flyback transformer FBT2. 2 switching circuits 12 and the first switching circuit 11, the first and second switching circuits 11, 12
The control terminal is the output terminal 01 of the frequency change detector 10,
02, and the frequency change detection circuit 10 is connected to the first and second switching circuits 11 and 12 to turn off both the first and second switching circuits 11 and 12 as the frequency of the horizontal synchronization signal applied to the horizontal synchronization signal terminal increases. a second state in which only the first switching circuit 11 is turned on, and a second state in which only the first switching circuit 11 is turned on; and a second state in which only the first switching circuit 11 is turned on;
The control terminal of the second switching element Q6 of the boost up circuit 14 is connected to the output terminal of the amplifier section 15. The amplifying section 15 is connected to the flyback transformer.
The output voltage on the secondary side of the FBT 2 is detected, and when the frequency of the horizontal synchronizing signal becomes higher in the third state and the output voltage falls below a predetermined value, the output voltage in the boost up circuit 14 is detected. Second
An overheat prevention high-voltage voltage stabilization circuit configured to output a control signal to turn on a switching element Q6 and ground one end of the primary side of the flyback transformer FBT2.