JPH06153004A - High voltage generating circuit - Google Patents

Abstract

PURPOSE:To obtain a high voltage generating circuit whose device constitution is simple. CONSTITUTION:A horizontal output transistor 4, a damper diode 2 and a resonance capacitor 3 are respectively juxtaposed on the primary-side of a flyback transformer 1. A switch control circuit 14 is connected to the horizontal output transistor 4. The switch control circuit 14 generates a switch control signal which pulse-modulates the drop amount of the high voltage output voltage and quickens timing for switching-on the horizontal output transistor 4 as the drop amount of high voltage output voltage is enlarged by the waveform shaping of a horizontal output driving signal, controls the switch operation of the horizontal output transistor 4 and stabilizes high voltage output voltage.

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 flyback pulse and applying the boosted output to the anode of a cathode ray tube.

[0002]

2. Description of the Related Art A high voltage generating circuit for applying a high voltage of several tens of KV to a cathode ray tube of a television receiver or a display device is usually provided with a high voltage stabilizing circuit for stabilizing a high voltage output voltage. As this high-voltage stabilizing circuit, there is also a method of controlling to increase the power supply voltage when the high-voltage output voltage decreases, but this method has a large power loss in the circuit element for voltage control, and There is a problem that the response of the high voltage stabilization control deteriorates due to the time constant of the large capacity capacitor used in the voltage control circuit.Recently, due to the switch operation, the flyback pulse generated on the primary side of the flyback transformer has A switch control method is used to control the magnitude of the peak value.

An example of a high voltage generating circuit based on this general switch control method is shown in FIG. In each of these circuits, a damper diode 2, a resonance capacitor 3, a horizontal output transistor 4 as a horizontal output switch element, a second switch element 5, and a drive power source 8 are provided on the primary side of the flyback transformer 1. The horizontal output transistor 4 is turned off to generate a flyback pulse by LC series resonance between the primary coil 6 of the flyback pulse 1 and the resonance capacitor 3, and the flyback pulse is boosted by the flyback transformer 1. And add it to the anode (not shown) of the cathode ray tube.

A high voltage output voltage applied to the cathode ray tube from the secondary coil 7 of the flyback transformer 1 is detected by a high voltage detecting means (not shown). Then, as the amount of drop of the high voltage output voltage increases, the timing of turning off,
That is, the control signal with the widened ON period is added to the second switch element 5 to perform the switch control of the second switch element 5.

In this type of circuit, during the period in which both the horizontal output transistor 4 and the second switch element 5 are on, the drive power source 8 side switches the second switch element 5, the primary coil 6 and the horizontal output transistor 4 from the drive power source 8 side. A current flows toward the primary coil 6, and electromagnetic energy is stored in the primary coil 6 due to the current flow. Therefore, in the ON period of the horizontal output transistor 4, as the amount of drop of the high voltage output voltage increases, delaying the OFF timing of the second switch element 5 increases the electromagnetic energy stored in the primary coil 6 and The peak value of the flyback pulse generated when the output transistor 4 is turned off also increases. Thus, as the amount of drop in the high voltage output voltage increases,
The high output voltage is stabilized by controlling the peak value of the flyback pulse generated on the primary side of the flyback transformer 1 to be large.

[0006]

However, in the conventional high voltage generation circuit, in addition to the horizontal output transistor 4 for generating the flyback pulse, the second switch element 5 for stabilizing the high output voltage is indispensable. Since it is necessary, there is a problem that the number of switch elements is increased and a plurality of input signals of these switch elements are also required, which complicates the circuit configuration.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to eliminate the need for a dedicated switch element for stabilizing a high output voltage in addition to a horizontal output switch element. An object of the present invention is to provide a high voltage generation circuit capable of stabilizing a high voltage output voltage with a simple circuit configuration.

[0008]

In order to achieve the above object, the present invention is constructed as follows. That is, according to the present invention, on the primary side of the flyback transformer, the drive power source, the horizontal output switch element, and the primary coil of the flyback transformer when the horizontal output switch element is off are set to L.
A high voltage generation circuit provided with a resonance capacitor for generating a flyback pulse by C resonance,
A switch control circuit for variably controlling the switch-on timing according to the amount of drop in the high-voltage output voltage is connected to the horizontal output switch element.

[0009]

In the present invention having the above-mentioned structure, the switch control circuit produces the switch control signal in which the switch-on timing is advanced according to the amount of drop of the high-voltage output voltage.
The horizontal output switch element is controlled by this switch control.

When the amount of drop of the high-voltage output voltage becomes large, the ON period of the horizontal output transistor 4 becomes long, so that the time during which the current flows from the driving power source side to the horizontal output switch element side through the primary coil becomes large, and the primary coil The electromagnetic energy stored in is also large. As described above, when the electromagnetic energy stored in the primary coil increases, the peak value of the flyback pulse generated by the LC series resonance between the primary coil and the resonance capacitor also increases when the horizontal output transistor 4 is turned off. High voltage output voltage stabilization is achieved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of a high voltage generating circuit according to the present invention. In the figure, a drive power source 8 is connected to one end side of the primary coil 6 of the flyback transformer 1, for example, a winding start side, and a horizontal output switch is connected in parallel with a series circuit of the primary coil 6 and the drive power source 8. The horizontal output transistor 4 as an element, the damper diode 2, and the resonance capacitor 3 are connected to each other, and the negative side of the drive power source 8, the anode side of the damper diode 2, and the emitter side of the horizontal output transistor 4 are respectively connected. It is connected to the ground side (ground side).

The high voltage end side of the secondary coil 7 of the flyback transformer 1 is connected to the anode of a cathode ray tube 11 via a high voltage rectifying diode 10. A series circuit of voltage dividing resistors 12 and 13 is connected to the high voltage side of the secondary coil 7, and the high voltage output voltage E _H is detected by the voltage dividing resistors 12 and 13.

A feature of this embodiment is that a switch control circuit 14 for variably controlling the switch-on timing according to the amount of drop of the high voltage output voltage is connected to the horizontal output transistor 4. This switch control circuit
Reference numeral 14 includes a comparison amplifier 15 such as an operational amplifier and a waveform shaping circuit 16. The comparison amplifier 15 compares the detected voltage of the high voltage output voltage with the reference voltage applied from the reference power supply 17, amplifies a signal corresponding to the difference, and a waveform shaping circuit 16
Add to.

A horizontal drive signal (HD signal) as shown in FIG. 2A is applied to the waveform shaping circuit 16 from a horizontal drive circuit (not shown). A switch control signal as shown in FIG. 2A that is pulse-modulated according to the amount of drop is created. In other words, the waveform shaping circuit 16 falls synchronously when the horizontal drive signal is turned off, rises within the on period of the horizontal drive signal, and the on timing is accelerated as the amount of drop of the high-voltage output voltage increases. That is, a switch control signal having a wider pulse width is generated and added to the base of the horizontal output transistor 4.

Next, the operation of this embodiment will be described with reference to the time chart of FIG. 2 and each operation circuit diagram of FIG. First,
In t ₁ ~t ₂ interval, at time t _1, by turning off the horizontal output transistor 4 in synchronism with the HD signal, the resonant capacitor 3 and the primary coil 6 starts series LC resonance, the driving power source 8 The current flowing through the primary coil 6 flows through the resonance capacitor 3, and the electromagnetic energy stored in the primary coil 6 is converted into the electrostatic energy of the resonance capacitor 3. At time t ₂ , all the electromagnetic energy on the primary coil 6 side is converted into electrostatic energy of the resonance capacitor 3, and at this time, as shown in FIG. 2C, the flyback pulse (collector pulse) has a peak. Become.

In the section from t _{2 to} t ₃ , the LC resonance between the resonance capacitor and the primary coil 6 causes the electrostatic energy of the resonance capacitor 3 to be converted back to the electromagnetic energy of the primary coil 6 and the horizontal output transistor. The collector voltage of 4 gradually decreases, and the collector voltage becomes zero at time t ₃ .

Then, the damper diode 2 is turned on for the damper period t _{3 to} t ₄ , a damper current flows from the ground side to the primary coil 6 side through the damper diode 2, and at the point of t ₄ , the damper diode 2 is turned on. When off, becomes free resonance period of the resonant capacitor 3 and the primary coil 6 in the interval t ₄ ~t _5.

FIG. 4 shows the relationship between the primary coil current and the collector voltage in the section from t _{4 to} t ₅ . Here, the collector voltage V _C is the power supply voltage of the drive power supply 8 E
_{When B} , V _C = E _B {1-cos t / √ (L
₁ C ₁ )}. Here, L ₁ is the inductance of the primary coil 6, C ₁ is the capacitance of the resonance capacitor 3, and t is time. The current I flowing through the primary coil 6 is I
= {E _B / √ (L ₁ / C ₁ )} sin {1 / √ (L
₁ C ₁ )} t. The current value It _{5 at} which the curve of the current I shown in FIG. 4B intersects the axis line of t ₅ is the initial value of the current I in the next transistor period t _{5 to} t ₆ . However, when the value of I is negative, the current value at the end of the damper period becomes the initial value of the current during the transistor period.

In the transistor period from t ₅ to t ₆ when the horizontal output transistor 4 is turned on at t ₅ , the horizontal output transistor 4 passes from the drive power source 8 side through the primary coil 6.
Current flows to the side, and electromagnetic energy is stored in the primary coil 6. The magnitude of the electromagnetic energy stored in the primary coil 6 increases as the horizontal output transistor 4 is turned on for a longer period, that is, the horizontal output transistor 4 is turned on earlier. Horizontal output transistor 4
Is turned off, the operation is returned to the initial operation of t ₁ to t ₂ , and the operation of the circuit is continued.

The peak value V _{CP of the} flyback pulse generated when the horizontal output transistor 4 is turned off.
Is represented by _{V CP = 2πf r L 1 I} P + V BE. Here, V _BE is the base-emitter voltage of the horizontal output transistor 4, f _r is f _r = 1 / 2π {√ (L ₁ C ₁ )}, and I _P is I _P = (E _B / L ₁ ) (t ₆ −
t ₅ ) + It ₅ . However, It ₅ is an initial value current when the horizontal output transistor 4 is turned on. When the number of coil turns of the primary coil 6 is N ₁ and the number of coil turns of the secondary coil 7 is N _H , the collector peak value V _CP generated on the primary side of the flyback transformer 1 is (N _H / N ₁ ) =
The high voltage output voltage is boosted n times. From this,
By varying V _CP , the high voltage output voltage can be varied, and in this embodiment, as the high voltage output voltage drops, the timing t _{5 at} which the horizontal output transistor 4 is turned on is advanced to increase the collector peak value V _CP. When the drop amount of the high-voltage output voltage is small, the timing of turning on the horizontal output transistor 4 is delayed to reduce the magnitude of the collector peak value V _CP generated on the primary side.
High voltage output voltage is stabilized.

As described above, in this embodiment, the switching of the horizontal output transistor 4 is controlled, whereby the stabilization of the high voltage output voltage is achieved, and the stabilization of the high voltage output voltage is achieved as in the conventional example. Since another dedicated switch element for performing the operation is not required at all, the circuit configuration becomes extremely simple and the circuit cost can be reduced.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, although the circuit of the above embodiment has a circuit configuration separated from the deflection system circuit, as shown in FIG. 5, a series circuit of a deflection yoke D _Y and an S-shaped correction capacitor C _S in parallel with the resonance capacitor 3 is provided. Can also be connected to form a deflection high voltage integrated type circuit configuration.

Further, as shown in FIG. 6, the resonance capacitor is composed of a series circuit of capacitors 3a and 3b, and the size of the resonance capacitance is varied by controlling the on / off of the switch 18, thereby making it possible to adjust the resonance capacitance in a wide range of frequencies. It can support multi-scan type.

Further, in the above embodiment, the horizontal output switch element is composed of a transistor, but this is a MOS.
It can be configured using other switching elements such as FET (field effect transistor).

[0025]

According to the present invention, the high output voltage is stabilized by controlling the on-timing of the horizontal output switch element for generating the flyback pulse by the switch-off operation. Unlike the conventional example, it is not necessary to use a dedicated switch element for stabilizing the high voltage output voltage, and the high voltage output voltage can be stabilized by controlling only one horizontal output switch element. As described above, it is not necessary to supply an input signal of a different system to each of the plurality of switches, and the circuit configuration is extremely simple, and accordingly, the circuit cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a high voltage generating circuit according to the present invention.

FIG. 2 is a time chart showing the operation of the circuit of the embodiment.

FIG. 3 is an explanatory diagram of operation timing of the circuit of the same embodiment.

FIG. 4 is an explanatory diagram showing a relationship between a collector voltage and a current during an ON period of a switch element.

FIG. 5 is a circuit diagram of another embodiment of the deflection and high voltage integrated type.

FIG. 6 is a circuit diagram of still another embodiment of the multi-scan type.

FIG. 7 is an explanatory diagram showing various circuit examples of a conventional high voltage generation circuit.

[Explanation of symbols]

 1 Flyback transformer 2 Damper diode 3 Resonant capacitor 4 Horizontal output transistor 6 Primary coil 8 Drive power supply 14 Switch control circuit

Claims (1)

[Claims] 1. A resonance capacitor for generating a flyback pulse by LC resonance of a drive power supply, a horizontal output switch element, and a primary coil of the flyback transformer when the horizontal output switch element is off, on the primary side of the flyback transformer. And a switch control circuit for variably controlling the switch-on timing according to the amount of drop in the high-voltage output voltage is connected to the horizontal output switch element. High voltage generator circuit.