JP2773633B2 - Focus voltage variable circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable focus voltage circuit used in a television receiver, a display device and the like using a cathode ray tube (CRT).

[0003]

[0002]

[0004]

2. Description of the Related Art FIG. 6 is a circuit diagram showing an example of a conventional focus voltage variable circuit. In FIG. 6, the primary winding L
A rectifying / smoothing circuit including a rectifying diode D1 and a smoothing capacitor C1 is connected to a high voltage (secondary winding L2) side of the high voltage transformer 1 having the primary and secondary windings L2, and a DC voltage Va
Is obtained. A series circuit including resistors R1, R2, R3, and R4 is connected between the high voltage terminal from which the DC voltage Va is extracted and the ground. The connection terminal of the resistors R2 and R3 is NP
Connected to the collector of the N-transistor Q1,
The connection terminal of R4 is connected to the non-inverting input terminal of the operational amplifier OP1.

[0005]

A reference voltage Vz is applied to the inverting input terminal of the operational amplifier OP1, and the output terminal is connected to the base of the transistor Q1. The emitter of the transistor Q1 is grounded via the resistor R6. The resistor R3, the operational amplifier OP1, and the transistor Q1 form a closed loop. And in such a configuration,
The voltage at the connection point between the resistors R1 and R2 is extracted as a focus voltage Vf as described later.

[0006]

Here, a description will be given of how the focus voltage Vf is controlled by varying the reference voltage Vz.
When the voltage V1 at the connection terminals of the resistors R3 and R4 is higher than the reference voltage Vz, the voltage at the base of the transistor Q1 increases, the collector voltage Vc decreases, and the voltage V1 decreases. Conversely, when the voltage V1 is smaller than the reference voltage Vz, the voltage at the base of the transistor Q1 decreases, the collector voltage Vc increases, and the voltage V1 increases. Therefore, the voltage V1 is stabilized so as to be equal to the reference voltage Vz.

[0007]

That is, Vc × R4 / (R4 + R3) = Vz
Vf = Va × R2 / (R1 + R2) + Vc × R1 / (R1 + R2) (1) Since Vf = Va × R2 / (R1 + R2) + (R3 + R4) × R1 × Vz / ｛(R1 + R2) / R4｝ (2), and the focus voltage Vf is controlled by varying the reference voltage Vz. The conventional focus voltage variable circuit shown in FIG. 6 is the one described in “Focus Voltage Variable Circuit” filed on Feb. 22, 1994 by the applicant of the present invention (reference number 405012267).

[0008]

FIG. 7 is a circuit diagram showing another example of a conventional focus voltage variable circuit. This conventional example is configured to take out a voltage from the middle of a high voltage winding. Winding L
In a high-voltage winding (corresponding to the secondary winding L2 in FIG. 6) in which 21 to L24 and diodes D21 to D23 are alternately connected in series, the resistors R1 to R4 are connected between the connection point between the winding L22 and the diode D22 and ground. Connected in series. Then, similarly to FIG. 6, the focus voltage Vf is variably extracted from the connection point of the resistors R1 and R2.

[0009]

[0007]

[0010]

FIG. 6 and FIG. 7 described above.
The focus voltage variable circuit shown in (1) can control the focus voltage Vf with a low DC voltage compared to a circuit in which the focus voltage Vf is varied by adjusting a mechanical variable resistor, and the focus voltage Vf can be automatically adjusted. Although it has features such as being easy and excellent in reliability, it has the following problems.

[0011]

In the above-described conventional focus voltage variable circuit shown in FIG. 6, when the transistor Q1 is off, the collector voltage Vc becomes: Vc = Va × (R3 + R4) / (R1 + R2 + R3 + R
4) It becomes the maximum. Since the focus voltage Vf is represented by the above equation (1), it is necessary to increase the collector voltage Vc in order to increase the variable range of the focus voltage Vf. However, the maximum withstand voltage of the transistor is 2 kV even if it is large, and the collector voltage Vc is 2 kV.
Even if it varies up to V, it is the focus voltage Vf
Does not become the variable range. Since the center voltage of the focus voltage Vf is 20 to 30% of the DC voltage Va, R1 /
The value of (R1 + R2) is 0.8 to 0.7, and 1.5 k
About V is a variable range. Therefore, what is shown in FIG.
There is a problem that the variable range of the focus voltage Vf cannot be made large.

[0012]

Also, in the conventional focus voltage variable circuit shown in FIG. 7, the value of R1 / (R1 + R2) is 0.25 when the center voltage is 40% of the DC voltage Va.
Even if the collector voltage Vc varies up to 2 kV, the variable range is about 500 V. Therefore, the one shown in FIG. 7 also has a problem that the variable range of the focus voltage Vf cannot be made large.

[0013]

The present invention has been made in view of the above problems, and has as its object to provide a focus voltage variable circuit capable of increasing a variable range of a focus voltage.

[0014]

[0011]

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention provides: (1) a high-voltage transformer, and a variable focus voltage which is obtained by changing a focus voltage from a high-voltage terminal of the high-voltage transformer. In the circuit, a high-voltage terminal of the high-voltage transformer is connected to a series circuit including first to third resistors, a focus voltage is taken out from a connection point between the first and second resistors, and the second and third resistors are connected.
The collector of the first transistor is connected to the connection point of the first resistor and the emitter of the first transistor is connected to the other terminal of the third resistor and the collector of the second transistor via the fourth resistor. A power supply is connected to a base via a fifth resistor, a collector of the second transistor is connected to a base of the first transistor via a sixth resistor, and an emitter is connected to a seventh resistor. And an output terminal of an operational amplifier for comparing the reference voltage with a collector voltage of the first transistor or a voltage obtained by dividing the collector voltage of the second transistor by a resistor, and connecting the output terminal of the operational amplifier to the base of the second transistor. A focus voltage variable circuit configured to vary the focus voltage by varying the reference voltage; In a focus voltage variable circuit provided with a lance and variably extracting a focus voltage from a high voltage winding or a high voltage terminal of the high voltage transformer, a first transistor is provided by extracting a voltage from an intermediate point or a high voltage terminal of the high voltage winding of the high voltage transformer. Connected to the collector of
The emitter of the first transistor is connected to the collector via a first resistor, and the base is connected to one terminal of one winding of a transformer via a second resistor, and the other end of the transformer is connected to the other end of the transformer. Is connected to the emitter of the first transistor, the other terminal of the other winding of the transformer is connected to the emitter of the second transistor, and the other terminal is grounded via a third resistor. Connecting the base of the second transistor to the anode of a diode, connecting the output terminal of an operational amplifier for comparing a voltage obtained by dividing the emitter voltage of the first transistor by resistance with a reference voltage to the cathode of the diode, A pulse obtained from another winding of the high-voltage transformer is applied to the base of the second transistor via a fourth resistor, and The it is to provide a focus voltage varying circuit, characterized by varying the focus voltage by varying.

[0016]

[0012]

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a variable focus voltage circuit according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing a first embodiment of a focus voltage variable circuit according to the present invention, and FIG.
FIG. 3 is a circuit diagram showing a second embodiment of the focus voltage variable circuit of the present invention, and FIG.
FIG. 4 is a circuit diagram showing a fourth embodiment of the focus voltage variable circuit of the present invention, and FIG. 5 is a diagram for explaining the operation of the third embodiment of the focus voltage variable circuit of the present invention. It is. 1 to 4, the same parts as those in FIGS. 6 and 7 are denoted by the same reference numerals, and the description of the same parts may be omitted.

[0018]

First, a first embodiment will be described. FIG.
A rectifying / smoothing circuit including a rectifying diode D1 and a smoothing capacitor C1 is connected to the high voltage (secondary winding L2) side of the high voltage transformer 1 having the primary winding L1 and the secondary winding L2, and the DC voltage Va Is obtained. Resistances R1, R2, R
3, a series circuit composed of R4 and R5 is connected. The connection terminals of the resistors R2 and R3 are connected to the collector of the NPN transistor Q2, and the connection terminals of the resistors R3 and R4 are connected to the NPN transistor Q2.
The resistor R8 is connected to the collector of the transistor Q1 and to the emitter of the transistor Q2 via the resistor R7.
Is connected to the base of the transistor Q2.
The base of the transistor Q2 is connected via a resistor R9 to another winding L3 on the secondary side of the high voltage transformer 1 and a diode D2.
It is connected to a DC power supply composed of a capacitor C2.

[0019]

Further, the emitter of the transistor Q1 is grounded via the resistor R6, and the base is connected to the output terminal of the operational amplifier OP1. A reference voltage Vz is applied to the inverting input terminal of the operational amplifier OP1, a voltage obtained by dividing the collector voltage Vc1 of the transistor Q1 by the resistors R4 and R5 is applied to the non-inverting input terminal. Vz is compared with a voltage obtained by dividing the collector voltage Vc1. Note that the resistor R4 and the operational amplifier OP
1. The transistor Q1 forms a closed loop. In such a configuration, the voltage at the connection point between the resistors R1 and R2 is extracted as a focus voltage Vf as described later.

[0020]

Here, a description will be given of how the focus voltage Vf is controlled by varying the reference voltage Vz.
The operations of the operational amplifier OP1 and the transistor Q1 are the same as those in FIG. Since the above-described closed loop operates so that the reference voltage Vz and the voltage obtained by dividing the collector voltage Vc1 of the transistor Q1 by resistance are equal, Vc1 = Vz × (R4 + R5) / R5 (3) Separate winding L3, diode D2, capacitor C2
Assuming that the voltage obtained from the DC power supply is Vo and the current flowing through the base of the transistor Q2 is sufficiently small,
The current IR9 flowing through the resistor R9 is as follows: IR9 = (Vo−Vc1) / (R8 + R9) (4)

[0021]

The collector current I of the transistor Q2 is
Q2 is the base-emitter voltage Vbe of transistor Q2
Is IQ2 × R7 + Vbe = IR9 × R8, IQ2 × R7 >> V
In the case of be, IQ2 = IR9 × R8 / R7 (5)

[0022]

Here, the resistors R7 and R8 are connected to the transistor Q
When the collector voltage Vc1 of 1 becomes 0, the transistor Q
2 is set so that the collector voltage Vc2 becomes zero. When the collector voltage Vc1 of the transistor Q1 is 0, the resistance R1,
The current flowing through R2 is Va / (R1 + R2). When the current becomes equal to the current IQ2, the current flowing through the resistor R3 becomes 0, and the voltage between the collector voltages Vc1 and Vc2 also becomes 0.

Va / (R1 + R2) is approximately (Vo-V
c1) × (R8 / R7) / (R8 + R9), and when the collector voltage Vc1 is the maximum (that is, when Vo), the current IR9 is 0 and the current IQ2 is also 0. At this time, the resistor R3 is set so that the collector voltage Vc2 becomes approximately 2 Vo.

[0024]

With the above setting, the transistor Q
2 and the collector voltage Vc1 of the transistor Q1 are approximately Vc2 = 2Vc1, and the focus voltage Vf is: Vf = Va * R2 / (R1 + R2) + Vc2 * R1 / (R1 + R2) = Va * R2 / ( R1 + R2) + 2Vz × (R4 + R5) / R5 × {R1 / (R1 + R2)} (6) The focus voltage Vf is controlled by varying the reference voltage Vz.

[0025]

In this embodiment, as described above, Vc2
Therefore, if the breakdown voltage of the transistors Q1 and Q2 is 2 kV, the collector voltage Vc1 of the transistor Q1 becomes 2 kV, and the collector voltage Vc2 of the transistor Q2 can be changed to about 2 times 4 kV.

[0026]

The configuration of the second embodiment shown in FIG.
Is connected to the connection point of the resistors R2 and R3. The operation principle of the second embodiment is the same as that of the first embodiment shown in FIG.
This is the same as the embodiment.

[0027]

Next, a third embodiment shown in FIG. 3 will be described. In FIG. 3, a voltage is taken out from an intermediate point (connection point between the winding L22 and the diode D22) of the high voltage winding in which the windings L21 to L24 and the diodes D21 to D23 are alternately connected in series, and the voltage is taken out to the collector of the NPN transistor Q3. Connecting. The resistors R11 and R1 are connected between the intermediate point and the ground.
2 and R13, and a capacitor C3
Is connected. The emitter of the transistor Q3 is connected to the connection point between the resistors R11 and R12, and the base is connected to the resistor R1.
4 is connected to one terminal of one winding (secondary side) of the transformer T1. The other terminal of the transformer T1 is connected to the emitter of the transistor Q3.

[0028]

Further, one terminal of the other winding (primary side) of the transformer T1 is connected to the emitter of the NPN transistor Q4, and the other terminal is grounded via a resistor R15. The collector of the transistor Q4 is connected to a low voltage source (12 V), and the base is connected to the anode of the diode D3. The cathode of the diode D3 is connected to the output terminal of the operational amplifier OP2. A reference voltage Vz is applied to a non-inverting input terminal of the operational amplifier OP2, and a voltage V1 obtained by dividing the emitter voltage of the transistor Q3 by the resistors R12 and R13 is applied to the inverting input terminal.
Is applied, and the operational amplifier OP2 compares the reference voltage Vz with a voltage obtained by dividing the voltage V1. Note that the resistor R1
A capacitor C4 having one end grounded at the connection point between R2 and R13.
Is connected. A pulse obtained from another winding L3 of the high-voltage transformer 1 is applied to the base of the transistor Q4 via a resistor R16. Then, in such a configuration, the emitter voltage of the transistor Q3 is extracted as the focus voltage Vf as described later.

[0029]

Here, a description will be given of how the focus voltage Vf is controlled by varying the reference voltage Vz.
First, the operation of the transformer T1 will be described. Assuming that the output voltage of the operational amplifier OP2 is Vop, the pulse of the other winding L3 shown in FIG. 5A is clipped by the diode D3, and becomes a pulse having the voltage Vop as shown in FIG. 5B. This pulse is supplied to the primary side of the transformer T1 through the transistor Q4, and a waveform as shown in FIG. 5C is obtained at point a on the secondary side. This FIG. 5 (C)
Is supplied to the base of the transistor Q3 via the resistor R14, and the transistor Q3 is driven.

[0030]

When the output voltage Vop of the operational amplifier OP2 increases, the pulse on the primary side of the transformer T1 also increases, and the pulse on the secondary side also increases. At this time, since the pulse induced at the point a also increases, the voltage V0 shown in FIG.
The collector current of the transistor Q3 increases and the resistance R11
The current flowing through is reduced. Therefore, the transistor Q3
, The focus voltage Vf also increases.

[0031]

Further, a closed loop including the operational amplifier OP2 will be described. When the voltage V1 divided by the resistors R12 and R13 is smaller than the reference voltage Vz, the operational amplifier OP
2 increases, and the voltage V0 shown in FIG. 5C also increases. At this time, the collector current of the transistor Q3 also increases, the current flowing through the resistor R11 decreases, and the emitter voltage of the transistor Q3 increases. Conversely, the voltage V1 divided by the resistors R12 and R13 is equal to the reference voltage Vz.
When it is larger, the emitter voltage of the transistor Q3 is reduced, and the voltage V1 divided by the resistors R12 and R13 is stabilized so as to be equal to the reference voltage Vz.

[0032]

Therefore, Vf × R13 / (R12 + R1
3) = Vz, that is, Vf = {(R12 + R13) / R13} × Vz (7), and the focus voltage Vf is controlled by varying the reference voltage Vz. In this embodiment, the variable range of the focus voltage Vf can be made larger than that of the conventional one. Further, in this embodiment, the voltage is taken out from the intermediate point of the high voltage winding, the power consumption can be reduced as compared with the configuration in which the voltage is taken out from the high voltage terminal, and the design relating to insulation against high voltage is facilitated.

[0033]

In the fourth embodiment shown in FIG. 4, a series circuit comprising resistors R1 to R4 is connected between the high voltage terminal of the transformer 1 and the ground, and the connection point of the resistors R1 and R2 is connected to the collector of the transistor Q3. The connection point between the resistors R2 and R3 is connected to the emitter of the transistor Q3. And the fourth
The operation principle of this embodiment is the same as that of the third embodiment shown in FIG.

[0034]

[0028]

[0035]

As described above in detail, the focus voltage variable circuit according to the present invention can control the focus voltage with a low DC voltage and can easily adjust the focus voltage automatically with the above-described configuration. In addition to its superiority, it has the advantage that the variable range of the focus voltage can be made larger than that of the conventional focus voltage variable circuit.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

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

FIG. 5 is a waveform chart for explaining a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a conventional example.

FIG. 7 is a circuit diagram showing another conventional example.

[Explanation of symbols]

 1 High voltage transformer C1 to C4 Capacitor D1 to D3, D21 to D23 Diode L1 to L3, L21 to L24 Winding OP1, OP2 Operational amplifier Q1 to Q4 NPN transistor R1 to R9, R11 to R16 Resistance T1 Transformer Vz Reference voltage

Claims (2)

(57) [Claims] 1. A focus voltage variable circuit comprising a high-voltage transformer, wherein a focus voltage is variably extracted from a high-voltage terminal of the high-voltage transformer. A series circuit including first to third resistors is connected to the high-voltage terminal of the high-voltage transformer. Then, the focus voltage is taken out from the connection point of the first and second resistors, and the collector of the first transistor is connected to the connection point of the second and third resistors. A power supply connected to the other terminal of the third resistor via a fourth resistor and a collector of the second transistor via a fifth resistor, and a collector connected to the base of the second transistor; Is connected to the base of the first transistor via a sixth resistor, and the emitter is grounded via a seventh resistor. An output terminal of an operational amplifier for comparing a reference voltage with a voltage obtained by dividing a collector voltage or a collector voltage of the second transistor by resistance is connected to the second terminal.
A focus voltage varying circuit configured to be connected to a base of the transistor, and varying the focus voltage by varying the reference voltage. 2. A focus voltage variable circuit comprising a high-voltage transformer, wherein a focus voltage is variably extracted from a high-voltage winding or a high-voltage terminal of the high-voltage transformer. And the collector of the first transistor is connected to the collector of the first transistor. The emitter of the first transistor is connected to the collector via a first resistor, and the base is connected to one of the windings of a transformer via a second resistor. Connected to one terminal, the other terminal of the transformer is connected to the emitter of the first transistor, and the other terminal of the other winding of the transformer is connected to the emitter of the second transistor. One terminal is grounded via a third resistor, and the base of the second transistor is connected to the anode of a diode. An output terminal of an operational amplifier for comparing a voltage obtained by dividing the emitter voltage of the first transistor by resistance and a reference voltage is connected to a cathode of the diode, and a pulse obtained from another winding of the high voltage transformer is connected to a fourth resistor. A focus voltage varying circuit configured to apply the voltage to a base of the second transistor via the first transistor, and vary the focus voltage by varying the reference voltage.