JP2650567B2 - High voltage generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage generating circuit for boosting a collector pulse and applying the boosted output to an anode of a cathode ray tube.

[0002]

2. Description of the Related Art In recent television receivers and display devices, high-definition and high-definition screens have been developed, and there is a demand for minimizing the influence of high-voltage output voltage on screen bending. Further, with the spread of computers, multi-scan type display devices that can be connected to all types of computers having different horizontal oscillation frequencies have become common. In order to increase the definition of the screen, a recent television receiver or display device is provided with a correction means for increasing the high-voltage output voltage by the drop when the high-voltage output voltage drops. The correction of the high output voltage is usually performed by controlling the peak value of the collector pulse generated on the low voltage coil side of the flyback transformer.

FIG. 9 shows a conventional high-voltage generating circuit (Japanese Patent Laid-Open No. 2-222374) provided with such a high-voltage correcting means. This circuit controls the on-period of the transistor 1 in accordance with the drop amount of the high-voltage output voltage by performing signal processing of a signal applied from the horizontal drive circuit side and a detection signal of the high-voltage output voltage. The larger the amount of drop, the larger the pulse width of the pulse control signal applied to the base of the transistor 1 (FIG. 10 (b)), and the greater the collector current (FIG. 10 (c)).
This is intended to increase the peak value of the collector pulse generated by the OFF operation of FIG. In other words, when the pulse width of the on period of the transistor 1 is increased, when the transistor 1 is turned off, the diodes 2 and
The magnitude of the collector current circulating in the closed loop returning to the diode 2 through the low-voltage coil 3 and the output transistor 4 in order increases, and the peak value of the collector pulse inevitably increases. As described above, by controlling the width of the ON period of the transistor 1, that is, the OFF time of the transistor 1, the peak value of the collector pulse is changed and the high-voltage output voltage is stabilized.

[0004]

However, in this type of high-voltage generating circuit, the collector current flowing from the diode 2 to the closed loop returning to the diode 2 through the low-voltage coil 3 and the output transistor 4 during the period in which the transistor 1 is turned off, Since a large amount of energy is required for the flyback operation, a large current flows in a closed loop, and the circulation of the current causes a loss when passing through each circuit element, resulting in a problem that circuit efficiency is deteriorated.

In the conventional high voltage generating circuit, it is difficult to turn on or off the switch when the voltage applied to the transistor 1 is zero (hereinafter referred to as zero cross switching operation).
The switching operation is performed in a state where the applied voltage is not zero voltage, so that a power loss occurs during the switching operation, and particularly when the switching operation is performed at a high frequency, the power loss of the switching becomes so large that it cannot be ignored. Occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to eliminate a loss caused by circulating a large current after turning off the transistor 1 and to improve circuit efficiency. An object of the present invention is to provide a high-voltage generating circuit that can effectively solve the problem of power loss during the switching operation of the transistor 1.

[0007]

The present invention is configured as follows to achieve the above object. That is, the present invention includes a first damper diode that is connected to the first switching element and second switching elements connected in series to the low pressure coil of the flyback transformer, the first switching element in parallel , The low-pressure carp
A first resonance capacitor forming a resonance circuit between the first resonance capacitor and the high-voltage output voltage applied to the cathode ray tube from the high-voltage coil of the flyback transformer.
A switch control circuit for controlling the on-period of the switching element to be longer.
With the switching element is connected in parallel a second damper diode, a second resonance capacitor are connected in parallel, the second switching element, the switch control circuit, at the latest in the first switching element It is configured to be controlled to turn on at the on start point and to turn off during the on period of the first switching element.

[0008]

In the present invention having the above structure, when both the first switching element and the second switching element are turned on, the second switching element, the low-voltage coil and the first switching element are connected from the driving power supply side. The passing current flows,
Energy is stored in the low voltage coil. In this state, the second
When the first switching element is turned off, a reverse voltage (negative pulse) is generated in the second capacitor, and as a result, the voltage of the driving power supply is canceled by the reverse voltage, and the second switching element turns off the first switching element. The peak value of the flyback pulse generated by the resonance operation between the first resonance capacitor and the low-voltage coil is reduced. The reverse voltage generated in the second capacitor increases as the width of the ON period of the second switching element decreases. The switch control circuit controls the ON period of the second switching element to increase as the drop amount of the high-voltage output voltage increases. As a result, the peak value of the flyback pulse increases as the drop amount of the high-voltage output voltage increases. Controlled in the direction,
The stabilization of the high output voltage is performed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a basic circuit of a high-voltage generating circuit according to the present invention, and FIG. 2 shows a circuit configuration of a first embodiment of the high-voltage generating circuit according to the present invention, which is a more concrete example of this basic circuit. It is shown. In FIG. 2, a dummy yoke 10 is connected in parallel to a low-voltage coil 12 of a flyback transformer 11. One end of a parallel circuit of the dummy yoke 10 and the low-voltage coil 12 has a transistor 13 as a first switching element. Are connected in series. A first damper diode 14 and a first resonance capacitor 15 are connected to the transistor 13 in parallel. The emitter of the transistor 13 is connected to a ground line (in this figure, an earth line). A horizontal output circuit (not shown) as shown in FIG.
Horizontal drive signal (HD)
Pulse) signal).

The other end of the parallel circuit of the dummy yoke 10 and the low-voltage coil 12 has an M functioning as a second switching element.
The source side of the OS FET (field effect transistor) 17 is connected. The drive power supply 18 is connected to the drain side of the MOS FET 17. MOS FET17
A second diode 20 and a second resonance capacitor 21 are respectively connected in parallel between the drain and the source. The second diode 20 may be externally connected to the MOS FET 17, but since the MOS FET 17 originally has a built-in diode in an equivalent circuit, the second diode 20 is not externally connected but built-in. A device using a diode may be used.

The high voltage end of the high voltage coil 24 of the flyback transformer 11 is connected via a high voltage rectifier diode 25 to the anode of a cathode ray tube (not shown). A bleeder resistor 26 is connected to the high voltage end of the high voltage coil 24, and a high voltage output voltage is detected by resistance division between the bleeder resistor 26 and the resistor 22. In this embodiment, a switch control circuit 16 generates a drive pulse signal for a MOS FET 17 using a detection signal of a high output voltage and a horizontal drive signal of a horizontal drive circuit (not shown).

The switch control circuit 16 includes a transistor 27 functioning as a third switching element,
28, a comparator 30, a buffer amplifier 31, and a switch drive circuit 32. The transistor 27 performs a switching operation upon receiving an inverted signal (-HD signal) of the horizontal drive signal as shown in FIG. 3A, and applies the switching signal to the differentiating circuit 28. The differentiating circuit 28 differentiates the switching signal to obtain a signal shown in FIG.
Is applied to the positive terminal of the comparator 30.

On the other hand, the buffer amplifier 31 amplifies the detection signal of the high output voltage and applies it to the negative terminal of the comparator 30. The comparator 30 compares the differential output applied from the differentiating circuit 28 with the detection signal of the high-voltage output voltage applied from the buffer amplifier 31 ((c) in FIG. 3), and as shown in (d) of FIG. And outputs a pulse signal that falls at the intersection of the lower right curve of the differential waveform and the detection signal of the high voltage output voltage. In other words, the comparator 30 generates a pulse signal with a wider pulse width as the amount of drop of the high-voltage output voltage increases,
This is added to the switch drive circuit 32.

The switch drive circuit 32 determines the rising position of the pulse signal by the transistor 13 shown in FIG.
In synchronization with the rising position of the drive pulse at or slightly after the drive pulse, the drive pulse signal shown in FIG. 3D, that is, the pulse width decreases as the drop amount of the high-voltage output voltage decreases, The drive pulse signal whose pulse width increases as the drop amount of the high-voltage output voltage increases becomes M
Applied to the gate of OS FET17.

This embodiment is configured as described above. Next, the stabilization operation of the high-voltage output voltage will be described with reference to the circuit of FIG. 2 and the time chart of FIG. First, when both the transistor 13 and the MOS FET 17 are on,
The collector current _ic of the transistor 13 flows from the driving power supply 18 through the MOS FET 17 and further from the dummy yoke 10 and the low voltage coil 12 through the transistor 13 to the ground line. At this time, assuming that the voltage of the drive power supply 18 is E _B and the inductance of the parallel circuit of the dummy yoke 10 and the low-voltage coil 12 is L, _ic increases with a linear slope determined by E _B / L. FIG. 3G shows a current waveform of _ic . Thus, the electric current flows through the dummy yoke 10 and the low-voltage coil.
By flowing through the coil 12, energy is stored in these coils 10, 12.

In this state, when the MOS FET 17 is turned off, a current flows from the second resonance capacitor 21 side to the transistor 13 side through the dummy yoke 10 and the low-voltage coil 12, and the electric charge is stored in the second resonance capacitor 21. As a result, D
The voltage between the portion indicated by the symbol and the ground is the second resonance capacitor 21 and the coil 1 as shown in FIG.
It decreases along the resonance curves of 0 and 12. In this state, when the transistor 13 is turned off, the current from the dummy yoke 10 and the low voltage coil 12 side is supplied to the first resonance capacitor 15.
And the energy stored in the coils 10 and 12 is transferred to the first and second resonance capacitors 15 and 21, and
The voltage of the second resonance capacitors 15 and 21 increased, and as shown in FIG. 3F, all the energy of the coils 10 and 12 was transferred to the first and second resonance capacitors 15 and 21. Sometimes flyback pulse (collector pulse)
At this time, the voltage of the second resonance capacitor 21 also reaches the peak.

Then, the energy of the first and second resonance capacitors 15 and 21 is returned to the dummy yoke 10 and the low-voltage coil 12 side, so that the voltages of the first and second resonance capacitors 15 and 21 are reduced. As the voltage decreases, the voltage between the portion indicated by the symbol D and the ground increases along the resonance curve between the coils 10 and 12 and the second resonance capacitor 21. Then, all the energy of the first resonance capacitor 15 is transferred to the coils 10 and 12, and after the flyback pulse shown in FIG. 3 (f) is created, the voltage across the second resonance capacitor 21 is gradually reduced to zero. The voltage is returned to the voltage level (when the voltage is about to be further reduced, the reverse current is returned to the drive power supply 18 through the second diode 20, so that the voltage across the second resonance capacitor 21 becomes smaller than the zero level. No). As described above, after the applied voltage of the MOS FET 17 is returned to zero voltage, the ON operation of the MOS FET 17 is performed, and at the same time or shortly before that, the transistor 13 is turned on.
Is turned on, the MOS FET 17 and the transistor 13
Are both turned on and the state described first is obtained, and the above operation is repeatedly performed.

As described above, in this embodiment, when the drop amount of the high-voltage output voltage is small, the width of the drive pulse of the MOS FET 17 becomes narrow, and as a result,
Since the ON period of 17 is short, the energy stored in the coils 10 and 12 is also small, and as the width of the drive pulse becomes narrower, the voltage of the reverse pulse when the MOS FET 17 is turned off increases, and the power supply voltage of the drive power supply 18 is reversed. Since the state is canceled by the pulse voltage, the amount of energy input to the LC series resonance circuit including the dummy yoke 10, the low-voltage coil 12 of the flyback transformer, and the first resonance capacitor 15 is reduced. The peak value of the flyback pulse generated when the switch is turned off becomes small. On the other hand, when the drop amount of the high-voltage output voltage is large, the width of the drive pulse of the MOSFET becomes wide, so that the energy stored in the coils 10 and 12 also becomes large,
Since the reverse pulse voltage generated by turning off the FET 17 decreases, the peak value of the flyback pulse generated when the transistor 13 turns off increases.

As described above, since the peak value of the flyback pulse generated as the drop amount of the high-voltage output voltage increases is controlled, the high-voltage output voltage is controlled to be constant, and the high-voltage output voltage is controlled to be stable. Is achieved.

In this embodiment, the MOS FET 17
Is turned on when the applied voltage is at the zero voltage level, and similarly turned off when the applied voltage is at the zero voltage level. At the time of this off driving, the drain-source voltage of the MOS FET 17 is Since it gradually rises along the resonance curves of the coils 10 and 12, the MOS FE
The drain-source voltage does not rise sharply by turning off T17. Therefore,
The MOS FET 17 can be reliably operated as a zero-cross switching operation. This zero-cross operation can eliminate switching power loss, and can further prevent generation of switching noise.

Further, since the second resonance capacitor 21 connected in parallel to the MOS FET 17 performs charging and discharging for each horizontal cycle, the power supply voltage of the driving power supply 18 is newly renewed for each cycle. becomes set are possible synonymous, moreover, the detection value of the high output voltage of the scanning period is under actual load is fed back during the scan period,
Since the MOS FET 17 is turned on / off without delay, the response speed becomes extremely fast, and the screen bending can be minimized.

Further, theoretically, the correction range of the high voltage is set to 10K.
Since it can be variably set in a wide range of V or more, it can sufficiently cope with a multi-scan display device that needs to secure a correction width of about 10 KV,
This is optimal for the multi-scan method.

FIG. 4 shows a second embodiment of the present invention. This embodiment is also provided with a switch control circuit for driving a second switching element such as a MOS FET, but this switch control circuit is omitted because it is the same as in the first embodiment. In this embodiment, a first circuit block 33 forms a parallel circuit of a first resonance capacitor 15, a first damper diode 14, and a first switching element, and a second resonance capacitor 21 and a second A second circuit block 34 constitutes a parallel circuit of the damper diode 20 and the second switching element, and the first circuit block 33 is provided between the winding start end of the low-voltage coil 12 and the ground. This is provided with a series circuit of a first circuit block 33 and a second circuit block 34, and stabilization control of a high-voltage output voltage is performed by a circuit operation similar to that of the first embodiment.

FIG. 5 shows a third embodiment of the present invention. In this embodiment, a series circuit of a first circuit block 33 and a second circuit block 34 is provided between the winding start end of the low-voltage coil 12 and the ground as in the second embodiment. The difference from the second embodiment is that the connection order of the first circuit block 33 and the second circuit block 34 is reversed,
The second circuit block 34 is connected to the ground side, and the other configuration is the same as that of the second embodiment, and performs the same circuit operations as those of the first and second embodiments. The same effect can be obtained.

FIG. 6 shows a fourth embodiment of the present invention. In this embodiment, one end of a dummy yoke 10 functioning as an inductance element is connected to the drive power supply 18 side, that is, the end of winding of the low-voltage coil 12, and the other end is connected to the first circuit block 33 and the second circuit block 33. This is because it is connected to the connection with the circuit block 34, and the other configuration is the same as that of the second embodiment. As described above, by interposing the choke coil 10 between the power supply connection side of the low-voltage coil 12 and the connection portion of the circuit blocks 33 and 34, the leakage flux of the low-voltage coil 12 of the flyback transformer 11 can be reduced. Thus, heat generation of the low-voltage coil 12 can be reduced.

FIG. 7 shows a fifth embodiment of the present invention. In this embodiment, a series circuit of a deflection yoke 35 and an S-shaped correction capacitor 36 is interposed between the series connection of the circuit blocks 33 and 34 and the ground. Thus, by providing the series circuit of the deflection yoke 35 and the S-shaped correction capacitor 36, a circuit configuration of a type in which the high voltage side circuit and the deflection side circuit are integrated can be obtained. In this embodiment, a switch control circuit 16 for controlling the driving of the second switching element is provided similarly to the above embodiments.

FIG. 8 shows a sixth embodiment of the present invention. In this embodiment, a second circuit block 34 is constituted by a parallel circuit of a second resonance capacitor 21, a second damper diode 20, and a second switching element.
A first circuit block 33 is configured by a parallel circuit of the first damper diode 14 and the first switching element, and the second circuit block 34 is set to the low voltage coil 12 side and the first circuit block 33 and the second circuit block 33 are connected to each other. A series circuit of the circuit block 34 is interposed between the low-voltage coil 12 and the ground, and furthermore, the circuit block 3
The first resonance capacitor 15 is connected in parallel to the series circuit of 3, 34. With such a circuit configuration, when the circuit of this embodiment is compared with the circuit of the second embodiment of FIG. 4, the circuit of FIG.
The electrostatic capacitance C _1, when the capacitance of the second resonant capacitor 21 and a C _2, a first resonance capacitor of the circuit of Figure 4
The capacitance C ₁ ′ of 15 is C ₁ ′ = C ₁ , the second resonance capacitor
By setting the capacitance C ₂ ′ of C 21 to C ₂ ′ = C ₁ + C ₂ , the circuit of FIG. 2 and the circuit of FIG. 8 have exactly the same circuit characteristics, which means that the circuit of FIG. Circuit block 33
The same circuit operation can be performed by setting the capacitance of the capacitor in the above-described relationship even when the connection order between the second circuit block 34 and the second circuit block 34 is reversed, which is very convenient in handling. Become.

It should be noted that the present invention is not limited to the above embodiments, but can take various embodiments. For example, in each of the above embodiments, the first switching element is a transistor
13 and the second switching element is MOS F
Although the ET17 is used, both the first and second switching elements may be formed by transistors or MOSFETs. Also, contrary to this embodiment, the first switching element can be formed by a MOSFET and the second switching element can be formed by a transistor. When the switching element is configured by a MOS FET, the built-in diode of the MOS FET can be replaced without externally connecting the first and second damper diodes because the MOSFET itself has a built-in diode in an equivalent circuit. Can be used as

A parallel switch circuit including the second switching element, the second damper diode, and the second resonance capacitor may be provided at an arbitrary position on a path from the driving power supply 8 to the ground line via the low-voltage coil 12. It is possible, and the interposition position is not limited to the embodiment.

Further, the switch control circuit constituting the present invention is not necessarily limited to the circuit of the embodiment.
Other configurations may be used as long as the length of time during which the second switch element is turned off after the first switch element is turned off can be controlled.

[0031]

According to the present invention, a second resonance capacitor is connected in parallel with the second switching element, and the second resonance capacitor and the inductance of the low-voltage coil perform resonance operation. Furthermore, the on-operation of the second switching element is operated at the same time as the on-operation of the first switching element at the latest, and the off operation of the second switching element is performed during the on-period of the first switching element. Therefore, the on / off switch operation of the first and second switching elements can be performed in a state where the applied voltage is zero voltage. In addition, when the second switching element is turned off, the voltage gradually decreases along the resonance curve of the second resonance capacitor, so that the voltage does not drop sharply when the switch is turned off. In addition, the zero cross operation of the second switching element can be reliably performed, the switching power loss can be eliminated, and the generation of switching noise can be prevented.

Further, according to the present invention, the peak value of the flyback pulse (collector pulse) is controlled by subtracting the voltage of the drive power supply by the back electromotive force when the second switching element is turned off. Therefore, unlike the conventional example, when the second switching element (transistor 1 of the conventional example) is turned off, a large amount of current is not circulated on the closed loop of the circuit to store energy in the coil. There is no power loss that occurs when circulating a large amount of current, and the circuit efficiency of circuit operation can be greatly increased.

[Brief description of the drawings]

FIG. 1 is a basic circuit diagram of a high voltage generation circuit according to the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of a high voltage generation circuit according to the present invention.

FIG. 3 is a time chart showing waveforms at various parts in a circuit according to the embodiment of the present invention.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 8 is a circuit diagram showing a sixth embodiment of the present invention.

FIG. 9 is a circuit diagram of a conventional high voltage generation circuit including a high voltage stabilization circuit.

10 is an operation explanatory diagram of the circuit in FIG. 9;

[Explanation of symbols]

 10 Dummy yoke 11 Flyback transformer 12 Low voltage coil 13 Transistor 14 First damper diode 15 First resonance capacitor 16 Switch control circuit 17 MOS FET 18 Drive power supply 20 Second damper diode 21 Second resonance capacitor

Claims (1)

(57) [Claims] 1. A a first switching element and second switching elements connected in series to the low pressure coil of the flyback transformer, the first switching element
A first damper diode connected in parallel, the low
The on-period of the second switching element is controlled to be longer as the amount of drop of the high-voltage output voltage applied from the high-voltage coil of the flyback transformer to the cathode ray tube increases, and the first resonance capacitor forming a resonance circuit with the pressure coil. in the high voltage generating circuit and a switch control circuit for the the second switching element together with the second damper diode connected in parallel, a second resonance capacitor are connected in parallel, the second A high-voltage generating circuit, wherein the switching element is controlled by a switch control circuit to turn on at the latest at the on-start point of the first switching element and to turn off during the on-period of the first switching element.