JP3045047B2 - Dynamic focus circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a dynamic focus circuit in a television receiver or the like, in which a parabolic waveform for dynamic focus does not affect the operation of high voltage control. It is.

[0002]

2. Description of the Related Art Dynamic focus is a technique in which a parabolic waveform is added to a DC voltage applied to a focus electrode of a picture tube so that the scanning periphery is high and the center portion is low in a deflection cycle, and the entire image of the picture tube is provided. This is a technique for obtaining an optimal focus state. FIG. 2 is a circuit diagram showing an example of a conventional dynamic focus circuit, which will be described below according to the reference numerals in the figure. First,
1 corresponds to an excitation pulse Vd from a preceding stage (not shown),
This is a horizontal deflection high voltage output circuit for generating a horizontal retrace pulse Vc. This horizontal retrace pulse Vc is guided to one end of the primary winding 2a of the next flyback transformer 2, and is boosted to the secondary winding groups 2b-1, 2b-2, 2b-3. Further, each boosted pulse is supplied to a high voltage rectifier diode group 3-1, 3-2, 3
The current is rectified by -3 and becomes a DC high voltage Ehv (DC high voltage line), which is applied to the anode a of the picture tube.

Here, the secondary winding groups 2b-1, 2b-2, 2b-
3 and the high-voltage rectifier diode groups 3-1, 3-2 and 3-3 each show three examples, but the number of sets may be other numbers depending on design conditions. It does not matter. This is the same for the circuits shown in FIGS. 1 and 3 described below.

[0004] The DC high voltage Ehv is also applied to a voltage dividing resistor 4 and a lower voltage (focus voltage) Ef on its first tap (or adjustable slider arm) T1.
And applied to the focus electrode f of the picture tube. Also,
The voltage dividing resistor 4 has a second tap T2, and the obtained reference voltage Er is applied to one of the input terminals of the next operational amplifier 6. Reference numeral 5 denotes a capacitor for removing ripples.

The reference voltage Er applied to the operational amplifier 6 is compared with a reference voltage Es applied to another input,
A control voltage E0 is generated at the output of the operational amplifier 6. Further, there is a voltage regulator 7 for exchanging the DC power supply voltage Eb for Eb0. This output voltage Eb0 is applied to the other end of the primary winding 2a of the flyback transformer 2 and the high voltage output circuit 1 of the horizontal deflection high voltage output circuit 1 is provided. Acts as a power supply voltage for operation. The output voltage Eb0 changes its value according to the control voltage E0 from the operational amplifier 6.

A circuit including the capacitor 5, the operational amplifier 6, and the voltage regulator 7 forms a high-voltage control circuit 8 as a whole. That is, in such a circuit, if the DC high voltage Ehv rises and the reference voltage Er tries to rise above the reference voltage Es, the operation of the voltage regulator 7 by the operational amplifier 6 and the control voltage E0 as its output will It is assumed that the polarity and the like are configured to decrease the value of the voltage Eb0. Then, the DC high voltage Ehv is always stabilized in such a manner that the reference voltage Er, which is the result of voltage division, matches the reference voltage Es. That is, the voltage is constant regardless of the fluctuation of the anode current Ia, which is the load current of the DC high voltage Ehv, and the fluctuation of the power supply voltage Eb.

By the way, reference numerals 9, 10, 1 described below
Even if there is no portion 1, the operation of supplying the operating voltage to the picture tube is performed, but in this case, the focus voltage Ef
Becomes a constant value of DC. In general, the optimal focus voltage of the picture tube is higher in the peripheral part than in the central part of the image, so even if a good focus is obtained in the central part, a focus shift occurs in the peripheral part and the sharpness of the image is reduced. Will drop.

Therefore, a parabolic waveform is superimposed so that the focus voltage Ef rises from the center at the left and right ends of the screen. Reference numeral 9 denotes a horizontal parabolic wave generation circuit which generates a parabolic waveform Vpb1 synchronized with horizontal deflection. The parabolic waveform Vpb1 may be a ship bottom type waveform in which the inclination of the central portion is made gentler than the original parabolic wave so that more accurate dynamic focus can be obtained depending on the form of the picture tube. This parabolic waveform Vpb1 is applied to the primary winding 10a side of the next focus transformer 10, and the second
On the side of the next winding 10b, a parabolic waveform Vpb2 which is boosted with a polarity such that the voltage becomes higher at the left and right ends of the horizontal deflection is obtained. The parabolic waveform Vpb2 is further superimposed on the focus voltage Ef through the coupling capacitor 11 as a parabolic waveform Vpb3.

Here, only the superimposition of a parabolic waveform relating to horizontal deflection, which has a high contribution to the focus improvement effect, is described. Of course, the parabolic waveform relating to vertical deflection can be superimposed together. Even better results are obtained. For this purpose, various measures are conceivable. For example, the capacitance of the coupling capacitor 11 is made large enough to have a low impedance with respect to the vertical frequency, and an appropriate vertical capacitor is connected in series with the secondary winding 10b of the focus transformer 10. What is necessary is just to insert a parabolic wave generation circuit.

FIG. 3 is a circuit diagram showing another conventional example. Since the same operation as that of FIG. 2 is performed in the same manner, detailed description thereof will be omitted. In FIG. 3A,
Reference numerals 12 and 13 denote voltage-dividing resistors provided in place of the voltage-dividing resistor 4 in FIG. 2. Reference numeral 12 denotes a voltage-dividing resistor exclusively for extracting the reference voltage Er from the second tap T4. This is a dedicated voltage-dividing resistor for extracting the focus voltage Ef from the first tap T3. Here, one end of the voltage dividing resistor 13 is connected to the cathode of the high voltage rectifier diode 3-3. This is because the required focus voltage Ef is sufficiently lower than one third of the DC high voltage Ehv. This is because the voltage Emv generated at this point (hereinafter referred to as DC medium pressure Emv) is often sufficient. Therefore, depending on the specifications of the picture tube used and the characteristics of the flyback transformer 2, the voltage dividing resistor 1
The connection point 3 may be located at another rectification stage, or may be directly connected to the DC high voltage Ehv similarly to the voltage dividing resistor 12.
In the circuit of FIG. 3B, one end of the voltage dividing resistor 14 for obtaining the reference voltage Er is also connected to the DC medium voltage Emv. 3 (a) and 3 (b) both compare the reference voltage Er generated at the tap T4 with the reference voltage Es.
The operation of finally fixing the DC high voltage Ehv and the application of the focus voltage Ef on which the parabolic waveform Vpb3 is superimposed to the focus electrode f are the same as those in the circuit of FIG.

[0011]

By the way, in the case of the circuit of FIG. 2, when the parabolic waveform Vpb3 is superimposed, this waveform is divided and the parabolic waveform Vpb4 appears at the tap T2. Then, the comparison operation with the DC reference voltage Es is not performed well, and the output (control voltage E0) of the operational amplifier 6 becomes a square wave reciprocating around the power supply voltage E of the operational amplifier 6 near zero level. Control becomes difficult. Further, if the parabolic waveform Vpb4 is large, the peak value may exceed the power supply voltage E of the operational amplifier 6. In such a case, the operation of the high-pressure control cannot be performed at all. In particular, the voltage value of the necessary parabolic waveform Vpb3 has increased with the recent trend toward a flat face and a wide picture tube,
At the same time, the parabola-shaped waveform Vpb4 also becomes large, causing a problem.

This is because the value of the capacitor 5 is increased and the parabolic waveform Vpb
It is also possible to solve by making 4 smaller. But,
This means that the response of the reference voltage Er when the DC high voltage Ehv fluctuates is delayed, and there are many problems in performance. Further, the existence of the coupling capacitor 11 itself is also due to the integration effect between this and the tap T1 of the voltage dividing resistor 4 and the high voltage side. The voltage response at the tap T1 has already delayed the actual DC high voltage Ehv movement. Since this naturally delays the reference voltage Er, this is also a problem.

On the other hand, in the circuit of FIG.
Since the tap T4 for obtaining r and the tap T3 for obtaining the focus voltage Ef are on different voltage-dividing resistors 12 and 13, respectively, the reference voltage Er is hardly affected by the parabolic waveform Vpb1. Absent. The coupling capacitor 1
The integration effect of 1 does not affect the response characteristics of the high-pressure control. However, in order to cope with a high voltage, the use of two large and expensive voltage dividing resistors (12, 13) is disadvantageous in cost. Naturally, the voltage dividing resistors 12,
The power consumed by the power supply 13 also increases.

Further, in the circuit of FIG. 3B, although the effect of stabilizing the high voltage is slightly reduced, the problems of cost and power are reduced.
This is more advantageous than the circuit of FIG. However, during the horizontal scanning period, since the rectifier 3-1 is in the cutoff state, the impedance of this portion is high, and the parabolic waveform Vpb3 superimposed on the focus voltage Ef appears at the DC medium pressure Emv.
Therefore, the parabolic waveform Vpb6 is also superimposed on the reference voltage Er at the second tap T5 of the voltage dividing resistor 14, and the same problem as in the circuit of FIG. 2 occurs.

[0015]

Therefore, in order to solve the above-mentioned problems, the present invention raises the parabolic waveform of the horizontal deflection period applied to the primary winding by the secondary winding and then applies it to the focus electrode. A focus transformer, connected between a DC high-voltage line for supplying a DC high voltage to the anode of the picture tube and ground, a first tap, and a second tap provided on the ground side of the first tap. A first resistor is connected to the focus electrode and supplies a focus voltage, and the second tap is connected to a high voltage control circuit and supplies a voltage for controlling the DC high voltage. In the dynamic focus circuit, a voltage waveform having a polarity opposite to that of the parabolic waveform applied to the focus electrode is generated in the focus transformer and applied to the second tap.
A dynamic focus circuit provided with a secondary winding is provided.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dynamic focus circuit according to an embodiment of the present invention will be described below with reference to FIG.
The same parts as those of the conventional circuits of FIGS. 2 and 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. As in the conventional circuits shown in FIGS. 2 and 3, a horizontal deflection high voltage output circuit 1, a flyback transformer 2, and a high voltage rectifier diode 3 are used to form a picture tube anode a.
The DC high voltage Ehv is applied thereto, and the DC high voltage Ehv is made constant by the action of a high voltage control circuit 8 composed of a capacitor 5, an operational amplifier 6, and a voltage regulator 7. The parabolic wave generating circuit 9 attached to the horizontal deflection high voltage output circuit 1 generates a parabolic waveform Vpb1 having a horizontal deflection period, which is boosted by a focus transformer 16, and then a DC focus voltage Ef by a coupling capacitor 11. Is superimposed as a parabola-shaped waveform Vpb3 on the same manner. Here, 15 is also a voltage dividing resistor, which has two taps T6 and T7 thereon. First tap (may be an adjustable slider arm) T
6 is connected to the focus electrode f of the picture tube and supplies a focus voltage. The reference voltage Er generated here is led from the second tap T7 to the input of the high voltage control circuit 8.

The focus transformer 16 applies a parabolic waveform Vpb1 to its primary winding 16a, and adds a secondary winding 16b
Obtaining the parabolic waveform Vpb2 which is stepped up and guiding it to the coupling capacitor 11 is the same as the conventional focus transformer 10. Here, a new point is that a tertiary winding 16c is newly provided. In the tertiary winding 16c, a parabolic waveform Vpb5 having a polarity opposite to that of the parabolic waveform Vpb2 appearing in the secondary winding 16b is generated. This parabolic waveform Vpb5 is applied to the reference voltage Er at the tap T7 via the capacitor 17 and the resistor 18.

Thus, in the circuits of FIGS. 2 and 3, the parabolic waveform Vpb superimposed on the reference voltage Er
4 can be canceled by adding a parabolic waveform Vpb5 of opposite polarity. That is, if the winding ratio between the secondary winding 16b and the tertiary winding 16c and the voltage dividing ratio by the capacitor 17 and the capacitor 5 are appropriately determined, the parabolic wave component is almost cancelled at the tap T7 and almost occurs. Disappears.

Here, even if the resistor 18 is omitted and the capacitor 17 is directly connected to the tap T7, the parabolic wave component on the tap T7 is greatly reduced, and this is often sufficient. However, the parabolic waveform Vpb4 originally contains a sawtooth wave voltage component corresponding to the voltage drop at the resistor 15 due to the charging / discharging current of the capacitor 5. Therefore, in order to cancel even the sawtooth wave component, it is better to insert the resistor 18 also on the parabola-shaped waveform Vpb5 side to generate a sawtooth wave voltage here. The resistor 18 can also be expected to have an effect of preventing a transient waveform at the time of discharge in the picture tube from being applied to the operational amplifier 6 through the focus transformer 16 and leading to damage.

As described above, in the circuit according to the present invention, a parabolic wave component does not appear in the reference voltage Er input to the high-voltage control circuit 8, so that the high-voltage control operation is ensured, and at the same time, the parabola having a sufficient voltage value is required. Since the waveform Vpb3 can be applied to the focus electrode f, the quality of the image on the picture tube is improved. Also, the brightness of the picture of the picture tube changes rapidly, and as a result, the DC high voltage Ehv or the DC medium pressure Emv
2 and FIG. 3, the charge / discharge current flows through the coupling capacitor 11 in the conventional circuits of FIGS. 2 and 3, and the response of the reference voltage Er is delayed by that amount, and the stability of the image may be significantly impaired. However, in the case of the circuit of FIG. 1 according to the present invention, the influence on the reference voltage Er due to the flow of the charge / discharge current of the coupling capacitor 11 is small. It is the secondary windings 16b and 3
This is because the current from the capacitor 17 flows into the capacitor 5 in a direction to cancel the influence of the charging / discharging current of the coupling capacitor 11 because the polarity of the secondary winding 16c is reversed. For this reason, when the image brightness is largely changed at the time of switching the screen, the time required for the DC high voltage Ehv and, consequently, the image amplitude to settle to a steady value is greatly reduced.

The circuit shown in FIG. 1 according to the present invention is different from the conventional circuit shown in FIG.
Since only one is used, there is an advantage that not only the cost and volume can be reduced but also the power consumption can be reduced. In addition, one end of the voltage dividing resistor 15 is of course connected to a DC high voltage E.
You can connect to hv. In this case, although the cost and the power are slightly increased, more accurate high-pressure stabilization becomes possible. Further, the voltage dividing resistor 15 is constructed like the voltage dividing resistors 13 and 14 of the circuit of FIG. 3B, and a parabolic waveform which cancels the parabolic waveform Vpb6 is added to the tap T5. You may comprise.

[0022]

As described in detail above, the dynamic focus circuit of the present invention ensures the operation of the high voltage control circuit, further increases the response speed, and has a sufficiently large value without obstructing the operation of the high voltage control. Can be superimposed on the focus electrode, which is useful for improving image quality. Further, if one voltage dividing resistor is formed, cost and power consumption can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing an example of a conventional dynamic focus circuit.

FIG. 3 is a circuit diagram showing another example of a conventional dynamic focus circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Horizontal deflection high voltage output circuit 2 Flyback transformer 4, 12, 13, 14, 15 Voltage dividing resistor 6 Operational amplifier 7 Voltage regulator 8 High voltage control circuit 9 Parabolic waveform generation circuit 10, 16 Focus transformer 11 Coupling capacitor T1, T3 , T6 First tap T2, T4, T5, T7 Second tap f Focus electrode a Anode of picture tube

Claims (1)

(57) [Claims] 1. A focus transformer applied to a focus electrode after boosting a parabolic waveform of a horizontal deflection period applied to a primary winding by a secondary winding, and a DC high voltage for supplying a DC high voltage to an anode of a picture tube. A voltage dividing resistor connected between the line and ground and having a first tap, and a second tap provided on the ground side with respect to the first tap, wherein the first tap has the focus Connected to the electrodes,
In a dynamic focus circuit that supplies a focus voltage and the second tap is connected to a high-voltage control circuit and supplies a voltage that controls the DC high voltage, the focus transformer includes an inverse of a parabolic waveform applied to the focus electrode. And a tertiary winding for generating a voltage waveform having a polarity of the second tap and applying the generated voltage waveform to the second tap.