JPH06292035A - Dynamic focus circuit - Google Patents

Abstract

PURPOSE:To provide a dynamic focus circuit for CRT monitor with a high speed horizontal scanning frequency with less power consumption, economy and ease of circuit design. CONSTITUTION:One terminal of a choke coil 30 connects to ground via a variable voltage power source 32 and the other terminal connects to ground via a switch 34. A 1st capacitor 36 is connected in parallel with the switch 34 and a series circuit comprising a dynamic correction focus coil 38 and a 2nd capacitor 40 is connected in parallel with the 1st capacitor 40. The switch is on-off operated by a pulse synchronously with a horizontal scanning frequency. A correction current of a parabolic waveform is obtained with a synthesis current iL between a resonance current i1 flowing in the off state and a resonance current i2 flowing in the on state.

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 for a cathode ray tube (CRT) monitor or CRT projection monitor using an electromagnetic focusing system.

[0002]

2. Description of the Related Art In general, a CRT monitor or a CRT projection monitor (hereinafter, simply referred to as a monitor) has different electron beam reaching distances in the central portion and the peripheral portion of the screen, and therefore, the best distance is obtained in the central portion of the screen. Even if the focus position is adjusted, the best focus position shifts in the peripheral portion as it is, and high resolution cannot be obtained.
Therefore, in order to obtain a high-resolution monitor, it is necessary to make a correction that dynamically changes the focusing magnetic field as the electron beam moves on the monitor screen.The circuit that performs this operation is a dynamic focus circuit. is there. In the case of a monitor using the electromagnetic focusing system, the dynamic focus circuit operates to supply a parabolic waveform current for which the current increases in the peripheral portion of the screen for the purpose of this correction.

Conventionally, a monitor using an electromagnetic focusing system is
Generally, an analog drive type dynamic focus circuit as shown in FIG. 4 is used. In FIG.
Reference numeral 10 indicates an amplifier, and the output of the amplifier 10 is grounded via a series circuit of a focus coil 12 for dynamic correction and a feedback resistor 14. Further, one input of the amplifier 10 is grounded, and the other input is connected to the midpoint of connection between the focus coil 12 for dynamic correction and the feedback resistor 14, and a parabolic waveform signal for dynamic correction via the input resistor 16. Is entered. A positive DC power source + E1 is connected to the terminal 18, and a negative power source -E2 is connected to the terminal 19.

The analog drive type dynamic focus circuit configured as described above amplifies a current waveform having a parabolic function shape, that is, a parabolic waveform current, and supplies the amplified current to the focus coil 12 for dynamic correction. Make a correction.

Further, a basic circuit for dynamic focus, which is designed to reduce power consumption as shown in FIG. 5, is a SID92 digest (SID92 DIGES).
T., pages 885-888, JM Perreut and B. Russell (B.
Roussel) co-authored “Concept of new device for cathode ray tube (A
New Device Concept for CR
Ts) ”. This circuit has two coils, a dynamic correction focus coil 20 having one terminal 28 connected to a positive power source + B, and a coupling coil 22 coupled to the correction focus coil 20 with a mutual inductance M. One terminal of the coupling coil 22 is grounded and the other terminal is connected to the other terminal of the correction focus coil 20 via the capacitor 24. The midpoint of connection is configured to be grounded via the switch 26.

The basic circuit for dynamic focus shown in FIG. 5 configured as described above operates as follows. In the scanning period TA, the switch 26 is in the open state, at which time a current flows through the resonance circuit formed by the correction focus coil 20, the capacitor 24, and the coupling coil 22, and a cosine-wave-shaped current is generated in the correction focus coil. Flows to 20. During the blanking period, the switch 26 is closed and the capacitor 24 and the coupling coil 2 are closed.
2. A reverse resonance current flows through the switch 26. At this time, the correction coil 20 has a mutual inductance M.
Since the correction focus coil 20 is coupled with, the reverse current for discharging the energy stored in the capacitor 24, that is, the current in the positive power supply + B direction flows.
The coupling coil 22 operates not only for coupling but also for supplying current during the blanking period. The switch 26
A thyristor or a series circuit of a diode and a MOSFET can be used as the thyristor, but the latter switch circuit is used when operating at high speed. Further, the current flowing through the correction focus coil 20 has a cosine waveform in the basic circuit, but is finally adjusted to have a parabolic waveform in an actual dynamic focus circuit (not shown) to perform dynamic focus correction.

[0007]

However, according to the dynamic focus circuit using the above-mentioned analog drive type amplifier, the effective current of the waveform flowing into the load must be constantly supplied from the power source + E1. Will be needed. In this case, when the power supply voltage is E, the supply current is I, and the load current flowing in the scanning period T is i as shown in FIG. 4, the required input power P (IN) is expressed by the following equation.

[0008]

[Equation 1]

This input power P (IN) is extremely large and reaches several tens of W in the case of a high-speed scanning monitor having a horizontal scanning frequency f of 100 KHz or more. For example, 25 inch CR
+ E for high-speed scanning of f = 170 KHz on T monitor
1 = 60V, −E2 = −30V, L = 30 μH, Rs =
Under the condition of 0.5Ω, the parabola current i is peak-to-peak.
The peak is about 3 A, and the direct current I supplied from the positive power supply is about 1 A. Therefore, the input power P (I
N) is very large as P (IN) = 60V × 1A = 60W, and there is a problem in terms of power consumption.

Further, in the case of a dynamic focus circuit which uses a coil coupled with mutual inductance M as described above and is constituted by a double resonance circuit, as shown in FIG. 5, a correction focus coil 20 and a coupling coil 22 are provided. Where L1 and L2 are inductances and C is the capacitance of the capacitor 24, the frequency f _{A of} the scanning period TA is determined by the mutual inductance M as shown in the following equation.

[0011]

[Equation 2]

Therefore, the correction focus coil 20 and the coupling coil 22 must be manufactured so as to have a predetermined mutual inductance M in advance. Therefore, in contrast to a general focus coil in which a fully insulated dynamic coil and a static coil are integrated, a special focus coil having a mutual inductance M and a mutual inductance M However, since it is one of the factors that determine the waveform, it is not easy to manufacture and it is not economical.

Therefore, an object of the present invention is to design a simple double resonance circuit, which consumes less power than an analog drive type dynamic focus circuit and does not require a coupling coil coupled by a mutual inductance M. It is an object of the present invention to provide a dynamic focus circuit capable of performing dynamic focus correction in.

[0014]

A dynamic focus circuit according to the present invention supplies a parabolic waveform current synchronized with a horizontal scanning frequency to a dynamic correction focus coil of a cathode ray tube using an electromagnetic focusing system. A choke coil having one end connected to a variable voltage power source, a first resonance circuit connected to the other end of the choke coil and flowing a first resonance current to a dynamic correction focus coil during a retrace period, A second resonance current which is connected to the other end of the choke coil and causes a second resonance current to flow to the dynamic correction focus coil during the scanning period.
Switch connected in series to the other end of the choke coil and in parallel to the first resonance circuit, and operated so as to be turned on during the scanning period in synchronization with the horizontal scanning frequency. It is composed of and.

In the dynamic focus circuit, the first and second resonance circuits also serve as the dynamic correction focus coil, and the dynamic correction focus coil, the first capacitor, and the capacitance larger than the first capacitor. Of a second capacitor having a large capacitance, and a switch connected in parallel with the first capacitor for synchronizing with the horizontal scanning frequency, and the first circuit when the switch is turned off. It is preferable that a resonance circuit is formed and the second resonance circuit is formed when the switch is turned on.

Further, in the dynamic focus circuit, the switch is turned on / off in synchronization with a horizontal scanning frequency, and the MOSFET flows to the second resonance circuit side through the MOSFET when the MOSFET is in an on state. It can consist of a series circuit with a diode that blocks current.

[0017]

According to the dynamic focus circuit of the present invention, a first resonance circuit that resonates during the blanking period and a second resonance circuit that resonates during the scanning period are configured by turning on / off the switch synchronized with the horizontal scanning frequency. Both resonance circuits share a dynamic correction focus coil as a constituent element to form a double resonance circuit. The switching connection of each resonance current waveform supplied by this double resonance circuit is smoothly performed by the energy accumulated in the choke coil, and a good parabolic waveform current can be obtained. The current having the parabolic waveform flows through the focus coil for dynamic correction, so that appropriate dynamic focus position correction is performed.

[0018]

Embodiments of the dynamic focus circuit according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a basic circuit configuration diagram of a dynamic focus circuit showing an embodiment of the present invention. Reference numeral 30 indicates a choke coil.
One terminal is grounded via a variable voltage power supply 32. The other terminal of the choke coil 30 is connected to the switch 34.
Grounded through. A first capacitor 36 is connected in parallel with the switch 34, and a series circuit of a dynamic correction focus coil 38 and a second capacitor 40 is connected in parallel with the first capacitor 36.

Next, the operation of the dynamic focus circuit according to the present invention shown in FIG. 1 constructed in this way will be described with reference to the voltage / current waveforms of the respective portions shown in FIG. The switch 34 is a switch circuit configured to be turned on / off by a pulse synchronized with the horizontal scanning frequency as described later, but is simply indicated by a switch symbol here. That is, the switch 34 is a switch that is turned on / off in synchronization with a pulse of a horizontal synchronizing frequency output from a horizontal oscillation circuit (not shown). 1 and 2, the voltage v _cp is a voltage generated on the choke coil side of the switch 34 via the choke coil 30, and the currents i ₁ and i ₂ are generated by the first resonance circuit and the second resonance circuit, respectively. I _L is a current flowing through the dynamic correction focus coil 38.

When the switch 34 is off, the voltage v
_cp changes as shown in FIG. 2A, and the first resonance circuit formed by a series circuit of the first capacitor 36, the correction focus coil 38, and the second capacitor 40 according to the voltage change. A current i ₁ flows through this. Here, the inductance of the correction focus coil 38 is L, and the capacitance of each of the first and second capacitors 36 and 40 is C.
1, C2 (however, C2 >> C1), the voltage of the power supply 32 is V
If the maximum value of cc and the current i ₁ is Io,
The current i ₁ flowing through the resonance circuit of is expressed by the following equation that changes with time t, and is a high-frequency current as shown in FIG.

[0022]

[Equation 3]

When the switch 34 is turned on, the first capacitor 36 is short-circuited and the second resonance circuit causes the correction focus coil 38 and the second capacitor 40.
And a series circuit with. At this time, the current i ₂ flowing through the second resonance circuit is represented by the following equation that changes with time t, and is a low-frequency current as shown in FIG.

[0024]

[Equation 4]

That is, the high frequency resonance current i ₁ during the off period T1 of the switch 34 and the low frequency resonance current i ₂ during the on period T2 of the switch 34 are repeated in synchronization with the horizontal scanning frequency. Therefore, the current i _L flowing through the dynamic correction focus coil 38, which is shared by the first resonance circuit and the second resonance circuit, is represented by the combination of these two currents (i ₁ + i ₂ ). The current has a parabolic waveform synchronized with the horizontal scanning frequency as shown in (D). At this time, the current i ₁ when the switch 34 is turned on and off
The connection portion between i and i ₂ does not become discontinuous due to the action of the choke coil 30.

The maximum value Io of the current i ₁ is t = 0.
The initial value Io is a value when i ₂ is supplied from the energy accumulated in the correction focus coil 38 at t = 0, and is represented by the following equation.

[0027]

[Equation 5]

As described above, although the basic circuit of the present application is a double resonance circuit as compared with the circuit of JM Perry et al., Which double-resonates using the coupling coil coupled by the mutual inductance M, A coupling coil is not necessary, and a correction waveform can be obtained only by the resonance between the correction focus coil 38 and the first and second capacitors 36 and 40, and the circuit design is easy.

FIG. 3 is a diagram showing a specific configuration example of the dynamic focus circuit according to the present invention. In FIG. 3, reference numeral 50 is a focus coil unit,
In the focus coil unit 50, a dynamic correction focus coil 52 (for example, an inductance 30
μH) and a capacitor 54 whose other end is grounded (for example,
And a capacitance of 0.047 μF) are connected in series. To the correction focus coil side terminal of this unit 50,
A capacitor 62 whose other end is grounded (for example, a capacitor 680
0pF / 1000V) is connected, and a variable voltage power supply Vcc (not shown) (for example, voltage 6V to 1) via a choke coil 60 (for example, inductance 2mH).
0V). The midpoint of connection between the choke coil 60 and the capacitor 62 is grounded via the switch circuit 70. The switch circuit 70 includes a diode 72 and an n
And a series circuit of the channel MOSFET 74,
Further, a gate drive circuit 80 having a general push-pull circuit configuration including npn and pnp transistors, resistors, diodes, etc. is connected to the gate terminal of the MOSFET 74 via an input resistor 90.

The dynamic focus circuit according to the present invention having the above-described structure performs the double resonance operation similar to that of the basic circuit shown in FIG. 1, and therefore generates the voltage / current waveform similar to that of FIG. A parabolic waveform current is supplied to the dynamic correction focus coil 52. The n-channel MOSFET 74 is used as the switch circuit 70 for high-speed operation, and the diode 72 is used.
Is used to block the current flowing in the direction of the choke coil 60 by the parasitic diode of the n-channel MOSFET 74. The gate drive circuit 80 is connected to a power source VG (for example, voltage 12V), and a 5V pulse whose phase is adjusted in synchronization with the horizontal scanning frequency is input to the input terminal 82. This input pulse is inverted and amplified in the gate drive circuit 80 to become a pulse of about 12V, and the input resistance 90
N-channel MOSFET 7 of switch circuit 70 via
4 gate. Where the gate drive voltage is 1
The high voltage of 2V is due to the n-channel MOSFET 74.
This is because the on resistance of is used sufficiently low.

In this embodiment, the horizontal scanning frequency is set to 1
As a measured value at a high speed operation of 70 KHz, a value of a power supply Vcc of 6.7 V and a supplied current I of 1.8 A was obtained. The coil current i _L of the parabolic waveform at this time was 4.5 A peak-to-peak. Therefore, the input power P (IN) in this case is about 12 W (6.7 V ×
It is 1.8 A), and it can be seen that the power consumption is lower than that of a dynamic focus circuit using a conventional analog drive type amplifier. The capacitors 62 and 54 in FIG. 3 correspond to the first capacitor 36 and the second capacitor 40 in FIG. 1, respectively.

[0032]

As is apparent from the above-described embodiments, according to the present invention, the power consumption required for dynamic correction is about 1/4 or less as compared with the conventional dynamic focus circuit using the analog drive type amplifier. It is possible to obtain a correct correction current.

Further, since the coils coupled by the mutual inductance M are used, the coupling coil, which is required in the case of the dynamic focus circuit composed of the double resonance circuit, becomes unnecessary, and the special focus coil is not used, which is economical. Not only is the circuit configuration simple. Therefore, even if the inductance value of the correction focus coil is already determined when designing the dynamic focus circuit, it is only necessary to determine the capacitances of the first and second capacitors and the voltage value of the variable voltage power supply for duplication. The respective currents i ₁ and i ₂ of the resonant circuit can be easily determined, and the circuit design is very easy.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the spirit of the present invention. Is.

[Brief description of drawings]

FIG. 1 is a basic circuit configuration diagram showing an embodiment of a dynamic focus circuit according to the present invention.

FIG. 2 is a voltage-current waveform diagram of each part showing the operation of the dynamic focus circuit according to the present invention shown in FIG.

FIG. 3 is a specific circuit configuration diagram showing another embodiment of the dynamic focus circuit according to the present invention.

FIG. 4 is a circuit diagram of an analog drive system showing an example of a conventional dynamic focus circuit.

FIG. 5 is a circuit diagram using a coupling coil showing another example of a conventional dynamic focus circuit.

[Explanation of symbols]

 10 amplifier 12 correction focus coil 14 feedback resistance 16 input resistance 18 terminal 19 terminal 20 dynamic correction focus coil 22 coupling coil 24 capacitor 26 switch 28 terminal 30 choke coil 32 power supply 34 switch 36 first capacitor 38 dynamic correction focus Coil 40 Second capacitor 50 Focus coil unit 52 Dynamic correction focus coil 54 Capacitor 60 Choke coil 62 Capacitor 70 Switch circuit 72 Diode 74 n-channel MOSFET 80 Gate drive circuit 82 Input terminal 90 Input resistance 90

Claims (3)

[Claims] 1. A dynamic focus circuit for supplying a parabolic waveform current synchronized with a horizontal scanning frequency to a focus coil for dynamic correction of a cathode ray tube using an electromagnetic focusing system, one end of which is connected to a variable voltage power supply. A coil, a first resonance circuit connected to the other end of the choke coil and flowing a first resonance current to the dynamic correction focus coil during a retrace period, and a second resonance circuit connected to the other end of the choke coil during the scanning period Second resonance circuit for flowing the resonance current of the above into the dynamic correction focus coil, is connected in series to the other end of the choke coil and is connected in parallel to the first resonance circuit, and is synchronized with the horizontal scanning frequency. And a switch that operates so that it is turned on during the scanning period. Kas circuit. 2. The first and second resonance circuits also function as a focus coil for dynamic correction, and the focus coil for dynamic correction, a first capacitor, and a second capacitor having a larger capacity than the first capacitor. And a switch that is connected in parallel to the first capacitor and that is synchronized with the horizontal scanning frequency, the first resonance circuit being configured when the switch is in an off state. The dynamic focus circuit according to claim 1, wherein the second resonance circuit is configured when the switch is turned on. 3. The MOSFET, wherein the switch is turned on / off in synchronization with a horizontal scanning frequency, and the MOSFET is connected to the second resonance circuit side when the MOSFET is on.
3. The dynamic focus circuit according to claim 1, comprising a series circuit with a diode that blocks a current flowing through the diode.