JPH0864444A - High-pressure control circuit - Google Patents

Abstract

PURPOSE: To provide a high-voltage control circuit which can control a high- voltage at a rapid response, has a small size and a low cost, high reliability even in the case of discharge in a tube, can constitute a circuit having small unevenness and drift, and has small danger of unnecessary oscillation of the circuit. CONSTITUTION: A reference voltage Eref generated from the tap point (d) of a voltage dividing resistor 11 provided in parallel with a focusing voltage dividing resistor 4 is compared with a reference voltage Es. The result is applied to a voltage control circuit 7. In this case, a DC feedback resistor 12 is provided between the inverting input voltage and the output terminal of an operational amplifier 6, and the gain as a comparator is intentionally lowered. When the resistance value Rn of the resistor 12 is set to the low value of the degree of Rn<10Ri with respect to the equivalent resistance value Ri in which the resistor 11 side is seen from the point (d), the constant operation of the intermediate voltage EV is weakened, and the characteristics have a negative gradient, while the high voltage HV has no positive gradient, and can be substantially constant.

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 stabilizing the anode voltage of a picture tube in a television receiver, etc.
The present invention relates to a high-voltage control circuit that is low in cost, highly reliable with respect to discharge in a tube, can be configured with less variation and drift, and has less risk of unnecessary oscillation of the circuit.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional high voltage control circuit. In FIG. 3, reference numeral 1 denotes a horizontal output circuit, which generates a pulse Vp having a horizontal deflection period at its output by adding an excitation waveform Vh having a horizontal deflection period from a preceding stage (not shown). Next, 2 is a flyback transformer, to which the above-mentioned pulse Vp is applied to one end of the primary winding 2a, and the DC voltage Ebo is applied to the other end.

On the secondary side of the flyback transformer 2, a plurality of secondary winding groups 2b-1, 2b-2, 2b-3, 2b- are provided.
4, 2b-5 are wound, and high voltage rectifying diodes 3-1, 3-2, 3-3, 3-4, 3-5 are connected in series with each of these winding groups. Since the primary pulse Vp is generated by being boosted in each secondary winding, a high voltage H is applied to one end of the hottest end of the group of these winding groups and the high voltage rectifying diode.
V is generated and guided to a point a which is an anode of a picture tube not shown.

Further, from one end of several sets on the cold end side of the set of the secondary winding and the high voltage diode, a high voltage H
An intermediate voltage FV with a voltage value lower than V is obtained, from which an adjustable voltage is obtained through the voltage dividing resistor 4. For example, in the circuit shown in FIG. 3, one of them is added to the focus electrode f of the above-mentioned picture tube and the other one is added to the screen electrode g to be its operating voltage.

On the other hand, the high voltage HV is connected to a voltage dividing resistor 5, and at the voltage dividing point b, a reference voltage Ere proportional to the high voltage HV.
f occurs. This reference voltage Eref is applied to one of the inputs of the next operational amplifier 6 and compared with the reference voltage Es applied to the other input.

[0006] Further, 1 of the flyback transformer 2
The circuit on the secondary side has a DC power supply voltage Eb from which the aforementioned DC voltage Ebo is obtained via a voltage control circuit 7, which is the primary winding 2a of the flyback transformer 2.
Is applied to one end of the horizontal output circuit 1 and becomes a power supply voltage for operating the horizontal output circuit 1. The DC voltage Ebo is controlled by the value of the control terminal c of the voltage control circuit 7, and the output of the operational amplifier 6 is connected to the point c. Note that, here, the set of the secondary winding and the high voltage diode is drawn in a state of five sets, but the number is arbitrary as long as it is a plurality of sets, and the following figures are the same.

In the circuit configuration shown in FIG. 3, let us consider a case where the picture tube displays a bright image and the anode current Ia thereof increases. If the series of circuits including the second voltage dividing resistor 5, the operational amplifier 6, and the voltage control circuit 7 is not provided, the high impedance value will decrease due to the internal impedance of the flyback transformer 2. Since this is not desirable from the viewpoint of image stability, it must be compensated by the circuit and the value of the high voltage HV should be kept as constant as possible regardless of the value of the anode current Ia. In the circuit shown in FIG. 3, if the high voltage HV is reduced, the reference voltage Eref resulting from the voltage division is reduced, which is below the reference voltage Es. Then
The output of the operational amplifier 6 is supplied to the voltage control circuit 7 by the voltage E
Change to raise bo.

As a result, even if the anode current Ia increases and the high voltage HV lowers, the voltage Ebo increases correspondingly and the peak value of the primary pulse Vp increases. It cannot be lowered, it is constant. This time,
The divided reference voltage Eref matches the reference voltage Es.

[0009]

While the circuit shown in FIG. 3 serves the purpose of stabilizing high voltage well, it also has some problems. One of them is that the second voltage dividing resistor 5 is connected between the high voltage HV and the ground, so that the structure becomes large and expensive due to the problem of withstand voltage. Further, since the reference voltage Eref is guided from the second voltage dividing resistor 5, which is a component directly connected to the high voltage HV, to the operational amplifier 6, the transient voltage oscillation when the picture tube causes an in-tube discharge occurs. There is also a problem in that the voltage is added to the operational amplifier 6 through the distributed capacitance associated with the voltage dividing resistor 5 and is damaged.

FIG. 4 shows another example of a conventional circuit for solving these problems. The difference from FIG. 3 is that
By eliminating the second voltage dividing resistor 5 directly connected to the high voltage HV,
Instead, the voltage dividing resistor 8 connected to the intermediate voltage FV is provided with a tap b for extracting the reference voltage Eref.
By doing this, the medium pressure FV is 20 to 30% of the high pressure HV.
Since a low value is enough, a large and expensive resistor is unnecessary. Further, since the voltage dividing resistor 8 is not directly connected to the high voltage HV, the reference voltage Eref is rarely affected by the discharge in the tube.

However, the circuit shown in FIG. 4 has a problem in response characteristics when the brightness of the picture tube image changes suddenly.
That is, even if the high voltage HV, and thus the intermediate voltage FV, changes rapidly due to the change in the anode current Ia, the reference voltage Eref at the tap b point cannot immediately follow. It is the capacitance 9 of the focus electrode f of the picture tube and the capacitance 1 of the screen electrode g.
Because there is 0, it is integrated by this. The values of the capacitors 9 and 10 are small, about several pF, but the influence cannot be ignored because the resistance value of the voltage dividing resistor 8 is as large as 100 MΩ or more.

As a result, the movement of the voltage Ebo is delayed, the high voltage HV fluctuates temporarily, and the image is distorted.
In particular, in order to avoid the influence of the ripple waveform induced here, the screen electrode g may be positively added with an external capacitance having a large value. Further, one end of the focus electrode f may be connected to the waveform generating circuit instead of being grounded to add a capacitor for superimposing the parabolic waveform of the deflection period on the focus electrode. The delay is so large that it becomes almost impractical.

Further, even during discharge in the picture tube, a large transient voltage may be generated due to the induction of the voltage of the focus electrode f, which appears at the point b connected to the same voltage dividing resistor 8 as the point f. As a result, the operational amplifier 6 may be damaged. This is an improvement over the circuit shown in FIG. 3 because it is not directly connected to the high voltage HV, but it is still insufficient in reliability.

Further, in FIG. 4, the movement of the medium pressure FV is detected to correct the movement of the high pressure HV. However, the medium pressure FV is not always proportional to the high pressure HV, and the high pressure HV is not constant at that time. In particular, there is a case where the value of the high voltage HV rises conversely as the current Ia increases. In such a case, the positive feedback is applied to the entire circuit to cause an oscillation state, and the value of the high voltage HV is It may vibrate in a unit cycle. Of course, in such a case, the size of the image changes drastically and it becomes impractical.

Further, a current If flows through the focus electrode f of the picture tube, although only slightly. This current If may or may not flow toward the electrodes, and is not constant depending on the picture tube. There is also a change over time. Therefore, the value of the reference voltage Eref is naturally influenced by the current If, which is a problem in terms of variation and drift.

[0016]

In order to solve the above-mentioned problems of the prior art, the present invention is connected to one end on the primary side of a flyback transformer and controls a DC voltage according to the voltage of a control terminal. Is supplied to the flyback transformer, a horizontal output circuit connected to the other end on the primary side of the flyback transformer to apply a pulse of a horizontal cycle, and a horizontal output circuit wound on the secondary side of the flyback transformer. A series circuit of a plurality of sets of secondary windings and a high-voltage rectifying diode, an anode of a picture tube connected to one end of the plurality of sets of secondary windings and a high-voltage rectifying diode on the high voltage side, and a plurality of sets of the plurality of sets. A first voltage dividing resistor, which is connected to a part of the secondary winding and a part of the high voltage rectifying diode on the low voltage side and obtains a focus voltage and a screen voltage, and is connected in parallel with the first voltage dividing resistor. And a second voltage divider resistor, One of the terminals is connected to a tap on the second voltage dividing resistor, the other of the input terminals is connected to a reference voltage, and an operational amplifier that supplies a control voltage to a control terminal of the voltage control circuit; Between the inverting input and the output of the amplifier, a direct current feedback circuit having its resistance value set so as to make the change of the anode voltage with respect to the change of the current flowing in the anode of the picture tube substantially constant is provided. The present invention provides a high voltage control circuit.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high voltage control circuit according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram for explaining the operation of the present invention. In FIG. 1, the same parts as those in FIGS. 3 and 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, a horizontal output circuit 1 receives an excitation signal Vh and generates a horizontal output pulse Vp, which is a secondary winding 2b-1 and 2b of a flyback transformer 2.
The voltage is boosted to b-2, 2b-3, 2b-4, 2b-5, and DC high voltage H is generated by the high voltage rectifier diode group 3-1, 3-2, 3-3, 3-4, 3-5.
What is V and is guided to the cathode ray tube a is basically the same as the conventional circuit shown in FIG. Further, by passing the DC power supply voltage Eb through the voltage control circuit 7, the control terminal c
It is also the same as obtaining the DC voltage Ebo which changes in accordance with the voltage of, and adding this to one end of the primary winding 2a of the flyback transformer 2 to use it as the power supply for operating the horizontal output circuit 1.

A characteristic point of the circuit shown in FIG. 1 is that a reference voltage Eref is newly provided in parallel with a voltage dividing resistor (first voltage dividing resistor) 4 for focusing (second voltage dividing resistor (second voltage dividing resistor)). It is obtained from the tap d point of the voltage dividing resistor 11). That is, in this case, the reference voltage Eref is generated not by the voltage division from the high voltage HV as in FIG. 3, but by the voltage division of the intermediate voltage FV for supplying the focus voltage. Therefore, the circuit of FIG. 1 applied to the voltage control circuit 7 as a result of comparing the reference voltage Eref with the reference voltage Es is essentially a stabilizing circuit of the medium voltage FV.

By the way, in the conventional circuit of FIG. 3, it is assumed that the high voltage HV is constant with respect to the change of the anode current Ia. At this time, the change of the intermediate pressure FV with respect to the anode current Ia is
Depending on the design method of the flyback transformer 2,
In general, as shown in FIG. 2 (A), the current Ia is often made to slightly decrease as the current Ia increases, and in this way, the focusing characteristics of the picture tube are kept good over the entire area of the current Ia. Be done.

When the flyback transformer 2 having such characteristics is used to obtain the reference voltage Eref by dividing the intermediate voltage FV as in the circuit shown in FIG. 1 or FIG. As shown in (B), the medium pressure FV is constant, but the high pressure HV increases with the increase of the anode current Ia. This is also a problem in that it appears as a change in image size, but the so-called negative resistance characteristic that the high voltage HV, that is, the anode voltage, also increases with the increase in the anode current Ia in this way is an oscillation phenomenon of the entire circuit. May occur, and the size of the screen may change oscillatingly and become unstable.

Therefore, in the circuit of the present invention shown in FIG. 1, a DC feedback resistor (DC feedback circuit) 12 is provided between the inverting input terminal and the output terminal of the operational amplifier 6 to intentionally increase the gain as a comparator. I am trying to lower it. In the conventional circuit as well, in order to maintain the stability of the circuit, the resistance value Rn of the DC feedback resistor 12 may be set to a very high value within a range that does not impair the characteristics of constant high voltage, and this may be inserted. At 1, the value is positively set to a lower value that deteriorates the constant voltage characteristic.

Specifically, with respect to the equivalent resistance when the voltage dividing resistor 11 side is viewed from the point d, that is, the resistance value Ri between the point d and the ground, Rn is conventionally a considerably large value with respect to Ri. However, the circuit shown in FIG. 1 has a low value of about Rn <10Ri. By doing so, as shown in FIG. 2 (C), the function of stabilizing the intermediate pressure FV is weakened and the characteristic has a negative slope, while the high pressure HV has no positive slope. It can be made almost flat, and characteristics similar to those of the conventional FIG. 2A can be maintained.

In the circuit shown in FIG. 1, only the stray capacitance of the transformer indicated by reference numeral 13 corresponds to the smoothing capacitor when the DC intermediate voltage FV is produced. Therefore, the medium pressure FV has a faster response than the high pressure HV side, which has a large response delay with respect to the change in the current Ia, due to the capacity of the aqua duck between the anode of the picture tube and the ground. . As a result, the movement of the reference voltage Eref is good and it corresponds to the change of the current Ia, resulting in less distortion of the image.

Further, the capacitance 9 of the focus electrode f and the capacitance 1 of the screen electrode g which have been problems in the conventional circuit shown in FIG.
In the present invention, 0 is also generated by the voltage dividing resistor 4 different from the voltage dividing resistor 11 for generating the reference voltage, so that it hardly affects the response characteristic. Therefore, in FIG. 1, it is possible to insert the capacitor 14 for removing ripples between the screen electrode g and the ground, and the focus electrode f.
It is also possible to connect a condenser 15 to and to add a parabola wave Vpb having a deflection period to one end of the condenser 15 to improve the focus quality around the picture tube.

Further, during the discharge of the picture tube, in FIG. 1 according to the present invention, the waveform of the excessive vibration is directly generated from both the anode a side and the focus electrode f side, and both the reference voltage Eref side and the focus electrode f side. Since the waveform of the excessive vibration does not directly appear on the reference voltage Eref side, the operational amplifier 6 is not endangered. At the same time, the focus current value also changes to the reference voltage E.
It does not affect ref directly and is advantageous in terms of drift and dispersion.

[0027]

As described in detail above, according to the high-voltage control circuit of the present invention, not only can high-voltage control with a quick response be performed, but it is also small in size, low in cost, and highly reliable against discharge in a tube. In addition, it is possible to form a circuit with less variation and drift, and there is also a lesser risk of unnecessary oscillation of the circuit.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram for explaining the operation of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional high voltage control circuit.

FIG. 4 is a circuit diagram showing another example of a conventional high voltage control circuit.

[Explanation of symbols]

 1 Horizontal output circuit 2 Flyback transformer 2b-1, 2b-2, 2b-3, 2b-4, 2b-5 High voltage winding 3-1, 3-2, 3-3, 3-4, 3-5 High voltage Rectifier diode 4 voltage dividing resistor (first voltage dividing resistor) 6 operational amplifier 7 voltage control circuit 11 voltage dividing resistor (second voltage dividing resistor) 12 DC feedback resistor (DC feedback circuit)

Claims (1)

[Claims] 1. A voltage control circuit connected to one end on the primary side of a flyback transformer to control and supply a DC voltage according to the voltage of a control terminal, and another voltage control circuit on the primary side of the flyback transformer. A horizontal output circuit connected to one end for applying a pulse of a horizontal cycle; a series circuit of a plurality of sets of secondary windings wound around the secondary side of the flyback transformer and a high-voltage rectifying diode; A pair of secondary windings and an anode of a picture tube connected to one end of the high-voltage rectifier diode on the high-voltage side, and a plurality of sets of secondary windings and a part of the low-voltage side of the high-voltage rectifier diode connected to the anode. , A first voltage dividing resistor for obtaining a focus voltage and a screen voltage, a second voltage dividing resistor connected in parallel with the first voltage dividing resistor, and one of the input terminals of the second voltage dividing resistor. Connected to the tap on the piezoresistor, The other of the terminals is connected to a reference voltage and an operational amplifier that supplies a control voltage to the control terminal of the voltage control circuit, and a change in current flowing through the anode of the picture tube between the inverting input and the output of the operational amplifier. A high-voltage control circuit, comprising: a DC feedback circuit whose resistance value is set so as to make the change of the anode voltage substantially constant.