JP2001157077A - High voltage control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high voltage control circuit, which executes high voltage control, free of giving influence to a horizontal deflection amplitude, nearly eliminates power loss at high voltage control, executes the correction of image distortion, such as the correction of right/left pin cushion distortion effectively and is realized, using a very simple constitution. SOLUTION: Two serially connected return resonance capacitors 9 and 10 are connected in parallel to a horizontal output transistor (switching element) 2. A diode 17 clamps the base part of a partial pressure pulse Vc0, generated at the connecting point of the capacitors 9 and 10 to a controlled voltage (second DC voltage) Ec3. A diode 18 is connected between the connecting point and a DC power voltage (first DC voltage) Eb and is made continuous in the partial period of the tip part of the pulse Vc0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage control circuit for controlling a high DC voltage supplied to a cathode of a picture tube, and more particularly to a high voltage control circuit capable of efficiently controlling only a DC high voltage with little effect on a horizontal deflection operation. It relates to a control circuit.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing a conventional horizontal deflection circuit. In FIG. 5, an excitation pulse Vdr from a horizontal excitation circuit in a preceding stage (not shown) is supplied to a primary winding of an excitation transformer 1, and a horizontal output transistor is supplied from a secondary winding thereof.
(Switching element) 2 supplies the base current Ib. In this case, the horizontal output transistor 2 performs a switching operation in cooperation with the damper diode 3 according to a well-known principle. During the off period of the switching operation, a collector pulse Vc of a half sine wave is generated at the collector terminal of the horizontal output transistor 2. The retrace resonance capacitor 4 is for determining the pulse width (return time) of the collector pulse Vc.

[0003] A series circuit of a horizontal deflection coil 5 and an S-shaped correction capacitor 6 is connected between the collector terminal of the horizontal output transistor 2 and the ground, and this series circuit has a sawtooth-shaped deflection having a horizontal deflection cycle. The current Iy flows and deflects the electron beam of the picture tube (not shown) in the horizontal direction.
The collector pulse Vc is supplied to one end of a primary winding 7a of the flyback transformer 7, and a boosted high-voltage pulse Vhv is generated in the secondary winding 7b. The other end of the primary winding 7a is connected to a DC power supply voltage Eb0, from which power is supplied to the circuit. The capacitor 16 is for smoothing the ripple current of the circuit. The high-voltage pulse Vhv is supplied to the high-voltage rectifier diode 8 and rectified to produce a DC high-voltage HV.
And supplied to the anode of a picture tube (not shown).

In FIG. 5, the DC power supply voltage Eb0 is
It is obtained from another DC power supply voltage (first DC voltage) Eb via the voltage control circuit 9. And this voltage control circuit 9
The value of the DC power supply voltage Eb0 which is the output voltage is controlled by the control voltage Ec1. For example, when the value of the DC power supply voltage Eb0 is increased, the value of the DC high voltage HV is also increased in proportion thereto.

FIG. 6 is a circuit diagram showing another conventional example, and FIG. 7 is a waveform diagram for explaining the operation of FIG. 6, which will be described together. 6, the same parts as those in FIG. 5 are denoted by the same reference numerals, and the description thereof will be omitted. 6 differs from FIG. 5 mainly in that an intermediate tap p is provided in the primary winding 7a1 of the flyback transformer 71, and the retrace time control circuit 10 is connected to the intermediate tap p. The other end of the primary winding is directly connected to the DC power supply E without passing through the voltage control circuit.
b. Flyback transformer 7
The retrace time control circuit 10 connected in parallel to a part of the primary winding 1 includes a rectifying diode 11, a capacitor 12,
It comprises a resistor 13, a transistor 14, a base resistor 15, and a control voltage Ec2.

Here, for example, when the control voltage Ec2 is low and the collector current Ic1 of the transistor 14 hardly flows, the pulse Vp generated at the tap p is substantially in proportion to the collector pulse Vc of the horizontal output transistor 2. That is, the voltage of the capacitor 12 once charged to the peak value of the pulse Vp hardly decreases due to discharging until the next pulse Vp comes. Accordingly, as shown in FIG. 7A, the conduction period of the diode 11 (that is, the charging period of the capacitor 12) ton1 is extremely short even at the subsequent peak of the pulse Vp, and the pulse shape is almost the same as the collector pulse Vc.

However, when the control voltage Ec2 increases and a large amount of the collector current Ic1 of the transistor 14 flows, the voltage stored in the capacitor 12 discharges through the resistor 13 and the transistor 14 until the next pulse and drops. . Therefore, as shown in FIG. 7B, in order to compensate for this discharge, the conduction period ton2 of the diode 11 is longer than in the case of FIG. 7A. During this conduction period, the capacitor 12
Charging period. Therefore, during the conduction period ton, the capacitor 12 is connected in parallel between a part of the primary winding 7a1 of the flyback transformer 7 and the part of the primary winding 7a1, which is equivalently impedance-converted and the capacitor 12 is connected. This means that the flyback resonance capacitor 4 is connected in parallel. As a result, during the conduction period ton, the resonance period of the collector pulse Vc becomes longer, so that the branch height value decreases.

From the above, when the collector voltage Ic1 of the transistor 14 increases by increasing the control voltage Ec2 and the conduction period ton becomes longer, the peak value of the collector pulse Vc of the horizontal output transistor 2 decreases. The value of the DC high voltage HV obtained by boosting and rectifying this decreases. That is, the DC high voltage value can be freely adjusted by the value of the control voltage Ec2. As the ton period becomes longer, the length of the pulse width (retrace time) tr of the collector pulse Vc becomes longer. That is, the circuit shown in FIG. 6 is a circuit that changes the high voltage by adjusting the length of the retrace time tr. On the other hand, the circuit shown in FIG. 5 described above can be said to be a circuit that changes the high voltage by adjusting the power supply voltage Eb0.

[0009]

In the conventional circuit shown in FIG. 5, when the DC power supply voltage Eb0 is changed in order to change the DC high voltage HV, the deflection current Iy flowing through the horizontal deflection coil 5 is also changed. There is a problem of doing it. Therefore, when trying to adjust the DC high voltage HV, the horizontal amplitude of the raster on the picture tube changes. In order to avoid this problem, the horizontal deflection coil 5 of FIG. 5 is not used as a dummy coil for horizontal deflection, but another set of similar circuits is provided for horizontal deflection. It is conceivable to use a horizontal deflection coil. However, in this case, there is a problem that the circuit scale increases and the cost increases.

In addition, it is not possible to incorporate a dedicated horizontal deflection amplitude control circuit, for example, a known saturable reactor or a diode modulator, and control the horizontal deflection coil current so as to cancel the change in the DC power supply voltage Eb0. is there. However, this also increases the DC power supply voltage Eb0 as the circuit scale increases.
Irrespective of the value of, it is very difficult to accurately keep the horizontal amplitude constant.

In the case of another conventional circuit shown in FIG.
In adjusting the high voltage, the DC power supply voltage Eb does not change and only the retrace time tr changes, so that the value of the current Iy flowing through the horizontal deflection coil 5 hardly changes. However, in order to adjust the high voltage HV, a large current Ic1 must flow, so that the resistor 13 and the transistor 1
4 is very large. Since this generates heat, the reliability of peripheral circuit elements may be impaired.
Since the current consumption Ib of the circuit from the power supply voltage Eb also increases, there is a problem that the power efficiency of the entire circuit also deteriorates. The present invention has been made to solve the above-described problems, and can perform high-pressure control without affecting the horizontal deflection amplitude, has almost no power loss during high-pressure control, and has image distortion such as left and right pincushion distortion correction. Correction can be performed effectively,
Moreover, an object of the present invention is to provide a high-voltage control circuit that can be realized with a very simple configuration.

[0012]

In order to achieve the above object, a switching element for performing an on / off operation in a horizontal deflection cycle, and a series circuit of a horizontal deflection coil and an S-shaped correction capacitor connected in parallel to the switching element. A return resonance capacitor group connected in parallel to the switching element and configured by a plurality of return resonance capacitors connected in series, and one end of a primary winding thereof is connected to one end of the switching element; A flyback transformer having an end connected to the first DC voltage, a high-voltage rectifier diode connected to one end of a secondary winding of the flyback transformer to output a DC high voltage, and the plurality of return resonance capacitors And a second DC voltage which is connected between the second DC voltage and a base point of a divided pulse generated at the connection point. And diode, said first and said connection point
And a second diode connected between the DC power supply and a second diode, the second diode being conductive during a partial period of the leading end of the voltage division pulse.

[0013]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG.
Is a characteristic diagram for explaining the operation of FIG. 1 and will be described together. In FIG. 1, the same parts as those in FIGS. 5 and 6 of the conventional example are denoted by the same reference numerals, and description thereof will be omitted.
In FIG. 1, the main differences from FIGS. 5 and 6 of the conventional example are as follows.
A point corresponding to the retrace resonance capacitor 4 of the conventional example is constituted by a retrace resonance capacitor group including two retrace resonance capacitors connected in series of the retrace resonance capacitor 9 and the retrace resonance capacitor 10; And a new control voltage Ec3
And a point where the diode 17 is connected so that the forward direction from the control voltage (second DC voltage) Ec3 toward the connection point c of the two retrace resonance capacitors 9 and 10 is established. The point is that the diode 18 is connected from the connection point c to the DC power supply voltage (first DC voltage) Eb for operation.

In FIG. 1, when the control voltage Ec3 is zero, the divided pulse Vc0 generated at the connection point c has a similar shape to the collector pulse Vc. The peak value is determined by the voltage division ratio of the two capacitors 9 and 10, which are set so that the peak value does not slightly reach the DC power supply voltage Eb as shown in FIG. Therefore, the diode 18 is off. The base of the time division pulse Vc0 is clamped to zero potential by the diode 17.

Next, when the control voltage Ec3 rises to a positive voltage as shown in FIG. 2 (B), the pulse base is also clamped by the control voltage Ec3, so that the pulse top is partially DC. The power supply voltage Eb will be exceeded. Then, during that time, the diode 18 conducts, and the current Id2 flows to charge the capacitor 16 on the DC power supply voltage Eb. This is equivalent to a short circuit of the capacitor 10 in terms of AC, and only the capacitor 9 operates as a retrace resonance capacitor during this period.

Accordingly, the capacitance of the retrace resonance capacitor is increased only during the conduction period ton1, so that the retrace time increases from tr in FIG. 2A to tr1 in FIG. The peak value of the pulse Vc also decreases. As a result, the DC high voltage HV also decreases substantially in proportion thereto. When the control voltage Ec3 is further increased,
As shown in FIG. 2C, the conduction period of the diode 12 is ton.
2 and the retrace time also extends to tr2. As a result,
According to the same principle, the DC high voltage HV is further reduced.

As described above, the circuit shown in FIG. 1 can freely adjust the value of the DC high voltage HV by moving the value of the control voltage Ec3. At this time, since the value of the DC power supply voltage Eb of the circuit does not change, the value of the deflection current Iy flowing through the horizontal deflection coil 5 hardly changes. Another feature of this circuit is that there is no extra power consumption associated with the high voltage control in the conventional example shown in FIG. That is, the current Id2 flowing during the conduction period of the diode 18 charges the smoothing capacitor 16, and the energy is used for the operation of the circuit through the primary winding 7a of the flyback transformer 7.

Therefore, when the control voltage Ec3 is increased to lower the DC high voltage HV, the current consumption Ib of the circuit from the DC power supply voltage Eb tends to decrease as shown in FIG. This is significantly different from the conventional example of FIG. 6 in which the circuit consumption current increases when the DC high voltage HV is lowered. However, as the control voltage Ec3 increases, the inflow current Id1 from the control voltage Ec3 also increases, so that the total power consumption of the entire circuit hardly changes as a result.

FIG. 4 is a circuit diagram showing another embodiment of the present invention. 4, the main difference from FIG. 1 is that resistors 19 and 20, a comparator 21, a voltage control circuit 22, and an amplitude modulation circuit 23 are added. Here, the DC high voltage HV is divided by the resistors 19 and 20 to obtain a small voltage Ehv proportional to the DC high voltage HV. The small voltage Ehv is supplied to the comparator 21 together with the DC reference voltage Es. The voltage Erf of the comparison result is output from the comparator 21 and supplied to the voltage control circuit 22. The voltage control circuit 22 converts the DC power supply voltage Ec0 according to the value of the voltage Erf to obtain a control voltage Ec3,
It is supplied as a clamp voltage for the diode 17.

In this way, for example, when the high voltage load current Ihv flowing through the picture tube anode increases and the DC high voltage HV tries to decrease, the control voltage Ec3 decreases to compensate for this and the pulse width of the collector pulse Vc (Return time) tr is shortened, and an operation of increasing the DC high voltage HV is performed. After all, the voltage Ehv obtained by dividing the DC high voltage HV is always equal to the DC reference voltage E.
The feedback circuit operates so as to match s, and the DC high voltage HV is stabilized.

The feature of the present invention shown in FIG. 4 is that the result of the high pressure adjustment does not affect the horizontal deflection. But,
In the conventional example, on the contrary, there is a problem that the adjustment of the horizontal deflection affects the high voltage value. For example, there is a case where the deflection current Iy of the horizontal deflection coil 5 is modulated by the amplitude modulation circuit 23 of FIG. For example, it is common practice to modulate the envelope of the deflection current Iy with a parabolic waveform Vpb having a vertical deflection period by using a saturable reactor, a diode modulator, or the like to correct the so-called left and right pincushion distortion of the image receiving screen. At this time, not only the deflection current Iy but also the DC high voltage HV is modulated, so that the right and left pincushion distortion correction effect may be reduced or the correction may not be performed accurately.

If the capacitor 24 shown in FIG. 4 is added to the high voltage section, this phenomenon will be reduced. However, since a capacitor that can withstand such a high voltage is large and extremely expensive, the present invention instead uses such a circuit as shown in FIG. Then, a waveform Vcl is applied to the voltage control circuit 22 so as to cancel the high voltage fluctuation caused by the amplitude modulation circuit 24. Then, the control voltage Ec3 output from the voltage control circuit 22 is similarly modulated, and the DC high voltage HV changes accordingly.
V is fixed. Of course, the operation of the voltage control circuit 22 at this time does not affect the modulation operation of the deflection current Iy by the amplitude modulation circuit 23.

[0023]

The high-voltage control circuit of the present invention can perform high-voltage control without affecting the horizontal deflection amplitude, has little power loss during high-voltage control, and is effective in correcting image distortion such as left and right pincushion distortion. This is an extremely excellent effect, for example, it can be realized with a very simple configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a characteristic diagram for explaining the operation of FIG. 1;

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

FIG. 5 is a circuit diagram showing a conventional horizontal deflection circuit.

FIG. 6 is a circuit diagram showing another conventional horizontal deflection circuit.

FIG. 7 is a waveform chart for explaining the operation of FIG. 6;

[Explanation of symbols]

 Reference Signs List 1 horizontal excitation transformer 2 horizontal output transistor (switching element) 3 damper diode 4, 9, 10 retrace resonance capacitor 5 horizontal deflection coil 6 S-shaped correction capacitor 7 flyback transformer 8 high voltage rectifier diode 16, 24 capacitor 17 diode (first 18 Diode (second diode) 19, 20 Resistance 21 Comparator 22 Voltage control circuit 23 Amplitude modulation circuit Vc Collector pulse Vc0 Dividing pulse Vpb Distortion correction waveform Eb DC power supply voltage (first DC voltage) Ec3 control Voltage (third DC voltage) Ec0 DC power supply voltage (second DC voltage) Es DC reference voltage Iy Deflection current Ib DC power supply current Id1, Id2 Current HV DC high voltage tr, tr1, tr2, tr3 Return time ton, ton1 , ton2 diode conduction period

Claims (3)

[Claims] A switching element for performing an on / off operation in a horizontal deflection cycle; a series circuit of a horizontal deflection coil and an S-shaped correction capacitor connected in parallel to the switching element; and a serial circuit connected in parallel to the switching element and connected in series. A flyback resonance capacitor group including a plurality of flyback resonance capacitors, wherein one end of a primary winding is connected to one end of the switching element, and the other end is connected to a first DC voltage. A high-voltage rectifier diode that is connected to one end of a secondary winding of the flyback transformer and outputs a high DC voltage; and a second DC voltage between a connection point between the plurality of retrace resonance capacitors and a second DC voltage. A first diode that is connected and clamps a base of a divided pulse generated at the connection point to the second DC voltage; Is connected between the source, the high voltage control circuit, characterized in that a second diode which conducts at some period of the distal end portion of the divided pulse. 2. A comparator for comparing a voltage proportional to the DC high voltage with a DC reference voltage and a third DC voltage, and the second DC voltage supplied to the first diode by the output of the comparator. The high-voltage control circuit according to claim 1, further comprising: a voltage control circuit that controls a value of the DC voltage and operates so that the DC high voltage is constant. 3. An amplitude modulation circuit for modulating a deflection current flowing through the horizontal deflection coil, and a modulation waveform for canceling the DC high voltage modulation effect generated by the amplitude modulation circuit is input to the second DC voltage to control the second DC voltage. The high-voltage control circuit according to claim 2, further comprising the voltage control circuit for controlling a value.