JP2003018426A - Dynamic focus circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To can generate a focus voltage optimum to a dynamic focus. SOLUTION: The dynamic focus circuit is provided with 1st and 2nd resonance circuits L14, T14, C14 and a capacitor C21 forming a waveform part with a 1st polarity of a focus voltage and a 2nd waveform part with the reverse polarity to that of the waveform part, and also with a switching circuit 21 in series connection with the capacitor C21 and a control circuit 22 that generates a prescribed control signal from a horizontal period pulse. The series circuit comprising the capacitor C21 and the switching circuit 21 is connected to the 1st and 2nd resonance circuits L14, T14, C14. The control signal is used to apply ON/OFF control to the switching circuit 21 for a horizontal period to selectively connect the capacitor C21 to the 1st and 2nd resonance circuits L14, T14, C14 thereby changing the resonance frequency of the 1st and 2nd resonance circuits L14, T14, C14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic focus circuit.

[0002]

2. Description of the Related Art In a television receiver using a CRT, in order to obtain an optimum focus on the entire display screen, the C
The RT focus voltage is changed according to the electron beam scanning position. Such focus voltage control is
Although called “dynamic focus”, a dynamic focus circuit as shown in FIG. 6 is considered as a circuit for realizing this dynamic focus.

That is, in FIG. 6, a horizontal drive pulse is supplied from the horizontal drive circuit 11 to the horizontal output circuit 12 to form a horizontal deflection current, and this horizontal deflection current is supplied to the horizontal deflection coil 13. Also, a switching transistor Q14, a diode D14, a coil L14,
The dynamic focus circuit 14 is constituted by the capacitor C14, the transformer T14 and the resistor R14. Then, as shown in FIG. 7A, a horizontal pulse PH that is at the “H” level during the period T1 and at the “L” level during the period T2 is extracted from the horizontal drive circuit 11 in the horizontal cycle TH (= T1 + T2). The pulse PH is supplied to the transistor Q14.

Then, in the period T1, the transistor Q14 is turned on by the pulse PH, so that the current ia flows in the line of power source → resistor R14 → primary coil of transformer T14 → coil L14 → transistor Q14 → ground, Coil L1
Energy is stored in 4. At this time, a current also flows in the line of capacitor C14 → coil L14 → transistor Q14 → ground.

Further, since the transistor Q14 is turned off by the pulse PH in the period T2, the coil L14 is turned in the period T1.
A current ib flows in the line of coil L14 → capacitor C14 → ground → diode D14 → coil L14 due to the energy stored in. A current ic flows from the coil L14 to the power supply line through the primary coil of the transformer T14 and the resistor R14. Further, the capacitor C14 is charged by the flow of the current ib, but this charging voltage causes ib
After = 0, a current id flows from the capacitor C14 to the power supply line through the primary coil of the transformer T14 and the resistor R14.

When the current ia flows, the coil L1
Since the transformer 4, the primary coil of the transformer T14, and the capacitor C14 act as a first resonance circuit, the secondary coil of the transformer T14 has a boundary between the period T1 and the period T2 as shown in FIG. 7B. A narrow sinusoidal pulse voltage VDF is output during a predetermined period TB centering on the time point. When the current id flows, the primary coil of the transformer T14 and the capacitor C14 act as a second resonance circuit, so that the remaining period TS (= TH-TB) is wide and the period TS is long.
A pulse voltage VDF having a polarity opposite to that of is output.

Therefore, this voltage VDF is supplied to the focus electrode of the CRT 15 as its focus voltage.
In this case, the period TB corresponds to the horizontal blanking period, and the period TS corresponds to the horizontal scanning period.

[0008]

By the way, when the dynamic focus is optimally executed, the waveform of the dynamic focus voltage VDF differs depending on the CRT 15. In particular, when the CRT is wide-angled as in recent years, the focus voltage VDF gradually changes during most of the period including the center of the period Ts (most of the range including the center of the screen), and the focus voltage VDF of the period TS increases. Near the start point and the end point (near the left and right sides of the screen), it is required that the waveform has a sharp change, that is, a so-called bathtub waveform. Moreover, the amplitude of the focus voltage VDF is also required to be considerably large, and depending on the size of the CRT 15, it is also required to be large, for example, 3.5 kVp-p.

However, in the case of the dynamic focus circuit as shown in FIG. 6, the focus voltage V of the bathtub waveform is
It is possible to form DF, but it is difficult to increase its amplitude, and if it is a bathtub waveform and it is attempted to increase it, the power loss of the circuit will increase.

The present invention is intended to solve such a problem.

[0011]

According to the present invention, for example, a first waveform portion having a first polarity of a focus voltage and a second waveform portion having a polarity opposite to the waveform portion are formed.
And a second resonance circuit, a capacitor, a switching circuit connected in series with the capacitor, and a control circuit that forms a predetermined control signal from a pulse having a horizontal period,
A series circuit of the capacitor and the switching circuit is connected to the first and second resonance circuits, and the switching circuit is turned on and off in a horizontal cycle by the control signal, so that the capacitor is connected to the first and second resonance circuits. The dynamic focus circuit is configured to be selectively connected to the resonance circuit to change the resonance frequencies of the first and second resonance circuits. Therefore, the first and second resonance frequencies change, and the waveform of the focus voltage changes in the preferred direction.

[0012]

In FIG. 1, a horizontal drive pulse is supplied from a horizontal drive circuit 11 to a horizontal output circuit 12 to form a horizontal deflection current, and this horizontal deflection current is supplied to a horizontal deflection coil 13. Further, the dynamic focus circuit 14 is configured as follows.

That is, between the power line and the ground,
Resistor R14, primary coil of transformer T14, and coil L
14 and the collector of switching transistor Q14
The emitter is connected in series with the transformer T14
A capacitor C14 is connected between the connection point of the primary coil and the coil L14 and the ground, and a diode D14 is connected between the collector of the transistor Q14 and the ground.

Further, from the horizontal drive circuit 11 to FIG. 7A.
As shown in FIG. 5, in the horizontal cycle TH, a horizontal pulse PH which is at "H" level during the period T1 and at "L" level during the period T2 is taken out, and this horizontal pulse PH is supplied to the base of the transistor Q14. The hot side of the secondary coil of the transformer T14 is connected to the focus electrode of the CRT 15.

In the present invention, the series circuit of the auxiliary capacitor C21 and the switching circuit 21 is connected in parallel with the capacitor C14. Further, the horizontal pulse PH output from the drive circuit 11 is the control circuit 2
2 and is supplied with "L" during the period Ta as shown in FIG. 2B.
And a control pulse PS that becomes "H" level is generated during the period Tb, and this pulse PS is generated by the switching circuit 2.
1 is supplied as a control signal to the switching circuit 2
1 is turned off when PS = "L" and turned on when PS = "H".

According to this structure, during the period Ta,
The coil L14, the primary coil of the transformer T14, the capacitor C14, and the capacitor C21 operate as a first resonance circuit. During the operation, the switching circuit 21 is switched from ON to OFF by the pulse PS. As a result, the capacitor C21 is changed from effective to ineffective, so that the resonance frequency of the first resonance circuit becomes high, and the peak value of the focus voltage VDF in the period Ta becomes large as shown by the solid line in FIG. , The waveform of the dotted line is the same as the waveform of FIG. 7B).

Also, during the period Tb, the primary coil of the transformer T14 and the capacitor C14 operate as a second resonance circuit, but the switch 21 is on for almost the entire period during the operation, and the capacitor C21. Is effective, the resonance frequency of the second resonance circuit becomes low, and as shown by the solid line in FIG. 2C, the focus voltage VD in the period T2
The peak value of F becomes small.

As a result, the focus voltage VDF is of a bathtub type and has a large amplitude as shown by the solid line in FIG. 2C, as compared with the case where the capacitor C21 is not switched between valid and invalid (the waveform of the dotted line in FIG. 2C). It becomes a voltage.

Thus, according to the above-mentioned dynamic focus circuit, only the capacitor C14 is effective for the resonance during the period when the first resonance circuit is operating. Therefore, by keeping the capacitance small, the resonance frequency is reduced. Becomes higher and the amplitude of the focus voltage VDF becomes larger, and since the capacitors C14 and C21 are effective for the resonance during the period when the second resonance circuit is operating, the resonance frequency becomes low and the focus voltage becomes low. The waveform of VDF becomes gentle.

Therefore, it is possible to obtain the bathtub type focus voltage VDF having a large amplitude. In that case, the dynamic focus voltage VDF of the target waveform is switched by switching the capacitor C21 between valid and invalid.
Therefore, the power consumption is not increased.

It is also possible to use a plurality of capacitors C21 and switch some of them during resonance, in which case the degree of freedom with respect to the waveform of the dynamic focus voltage VDF is increased.

FIG. 3 shows a specific example of the switching circuit 21 and the control circuit 22. That is, as the switching circuit 21, the drain-source of the p-type FET (Q21) and the parallel circuit of the diode D21 are connected. In addition,
The diode D21 may be incorporated in the FET (Q21).

In the control circuit 22, the horizontal pulse PH output from the drive circuit 11 is applied to the differentiating circuit 22.
1 as shown in FIGS. 4A and 4B (FIG.
(Same as A), every time the horizontal pulse PH rises,
The rising differential pulse PB is taken out.

This pulse PB is applied to the voltage comparison circuit 2
The reference voltage VTH is supplied to the non-inverting input terminal of the comparator 22 and the reference voltage VTH is supplied to the non-inverting input terminal of the comparator 22. As shown in FIG. 4C, when PB> VTH, the level becomes “L”, and PB ≦ VTH. At this time, the pulse PC which becomes "H" level is taken out. At this time, the falling point of the pulse PC coincides with the rising point of the horizontal pulse PH. Then, this pulse PC is applied to the clamp circuit 223.
Is supplied to the gate of the FET (Q21) through.

According to this structure, the FET (Q21) is turned on during the period of PC = "L", but the FET (Q21) is turned on.
When turned on, the capacitor C21 is connected in parallel to the capacitor C14 and operates as a part of the first resonance circuit, and a positive-direction pulse portion of the focus voltage VDF is formed.

After that, when the FET (Q21) is turned off in the period of PC = “H”, the capacitor C14 contributes to resonance, but the capacitor C21 does not contribute to resonance, and the capacitor C21 has As shown in 4D, a negative pulse voltage VD is generated. And this pulse voltage VD
When the voltage rises again and tries to exceed the ground level, the diode D21 is turned on and the capacitors C14 and C21 are again connected in parallel. Then, this diode D
While 21 is on, the pulse PC causes the FET (Q2
1) is turned on again.

Since the above operation is repeated,
From the transformer T14, a focus voltage VDF having a bathtub type and a large amplitude can be obtained.

In FIG. 5, the switching circuit 21 is a FET.
(Q21) and diode D21, and the FET (Q21) is an n-type. Then, the pulse PC output from the comparison circuit 222 is supplied to the gate of the FET (Q21) through the transformer T22.
Therefore, also in the case of this circuit, it is possible to obtain the bathtub type focus voltage VDF having a large amplitude as in the circuit of FIG.

In the above description, if the magnitude of the reference voltage VTH supplied to the comparison circuit 222 is changed, the pulse P
Since the pulse width of C can be changed, the waveform of the bathtub of the focus voltage VDF can be changed.

[List of abbreviations used in this specification] CRT: Cathode Ray Tube FET: Field Effect Transistor

[0031]

According to the present invention, it is possible to obtain a bathtub type focus voltage having a large amplitude. And
In that case, since the dynamic focus voltage of the target waveform is obtained by switching the capacitance of the capacitor, there is no increase in power consumption.

Further, it is possible to provide a plurality of capacitors for resonance and switch some of them during resonance. In that case, the degree of freedom for the waveform of the dynamic focus voltage can be increased.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram for explaining the operation of the circuit of FIG.

FIG. 3 is a connection diagram showing another embodiment of the present invention.

FIG. 4 is a waveform diagram for explaining the operation of the circuit of FIG.

FIG. 5 is a connection diagram showing another embodiment of the present invention.

FIG. 6 is a connection diagram for explaining the present invention.

FIG. 7 is a waveform diagram for explaining the operation of the circuit of FIG.

[Explanation of symbols]

11 ... Horizontal drive circuit, 12 ... Horizontal output circuit, 13 ...
Horizontal deflection coil, 14 ... Dynamic focus circuit,
15 ... CRT, 21 ... switching circuit, 22 ... control circuit

Claims (2)

[Claims] 1. A first and a second resonance circuit forming a waveform portion of a first polarity of a focus voltage and a second waveform portion of a polarity opposite to the waveform portion, a capacitor, and a capacitor connected in series. And a control circuit for forming a predetermined control signal from a pulse having a horizontal cycle, a series circuit of the capacitor and the switching circuit is connected to the first and second resonant circuits, and By controlling the switching circuit to be turned on and off in a horizontal cycle by a control signal, the capacitor is selectively connected to the first and second resonant circuits to connect to the first resonant circuit.
And a dynamic focus circuit adapted to change the resonance frequency of the second resonance circuit. 2. The dynamic focus circuit according to claim 1, wherein a plurality of series circuits of the capacitor and the switching circuit are provided, and the waveform of the focus voltage is changed by switching and connecting the plurality of series circuits. Dynamic focus circuit.