Deflection yoke for color cathode ray tube

BACKGROUND OF THE INVENTION

This invention relates to a deflection yoke which includes a raster rotation coil, and more particularly to a deflection yoke which allows compatibility of correction of raster distortion other than raster rotation performed using a raster rotation coil and correction of misconvergence performed by producing a difference in current between an upper side horizontal deflection coil and a lower side horizontal deflection coil.

Some deflection yokes for a color cathode ray tube include a raster rotation coil. A raster rotation coil is frequently located on the front side of a deflection yoke, that is, adjacent to a screen with respect to a cathode ray tube.

FIG. 1

is a perspective view showing an entire deflection yoke which includes a raster rotation coil, and

FIG. 2

is a side elevational view showing only coils and a DY core of the deflection yoke of FIG.

1

.

A pair of upper and lower saddle type horizontal deflection coils

3

are wound around a horizontal deflection coil bobbin

1

. A pair of left and right saddle type vertical deflection coils

7

are wound around a vertical deflection coil bobbin

5

on the outer sides of the horizontal deflection coils

3

.

A DY core

9

made of ferrite is mounted such that it surrounds the vertical deflection coils

7

. An annular (circular, polygonal or the like) raster rotation coil

11

is mounted along an outer periphery of the deflection yoke on the front side of the deflection yoke. It is to be noted that, in

FIGS. 1 and 2

, reference numeral

13

denotes an adjustment knob,

15

an adjustment coil,

17

a rear cover, and

19

a front cover.

The raster rotation coil

11

has a winding of several hundreds turns of a nylon-coated wire of a diameter of approximately ø 0.2 to ø 0.4 mm.

The raster rotation coil

11

is usually used in order to correct rotation of a raster appearing on the screen of the cathode ray tube around an axis of the tube.

For example, if a location of a receiver in which a cathode ray tube is used is varied, then the influence of the terrestrial magnetism upon the cathode ray tube varies. This sometimes rotates the raster in a fixed direction into an inclined state.

In such an instance, the raster in an inclined state is corrected by DC current flowing in the raster rotation coil.

In addition, a magnetic field generated by the raster rotation coil interferes with the deflection coil. However, if fixed DC current flows in the raster rotation coil, then also the magnetic field is fixed and it does not occur that induction current flows in the deflection coil as a result of the interference. Consequently, a convergence characteristic is not influenced by the interference.

If a triangular wave current having a period equal to a vertical deflection period or an arbitrary period or an alternating current of an arbitrary waveform is supplied to the raster rotation coil

11

, then also the amount of rotation of the raster varies in response to the amount of the current. This allows correction of a distortion other than raster rotation, for example, correction of trapezoid distortion or the like of a raster. This technique is effective to products for which a severe quality in regard to raster distortion is required, for example, to display units for computers.

However, since the magnetic field generated by the raster rotation coil varies with respect to time, induction current flows in the deflection coil by an influence of the temporal variation of the magnetic field. This current causes a variation of the convergence characteristic and gives rise to so-called misconvergence.

A countermeasure against this problem has been proposed already. Referring to

FIG. 3

, a pair of coils

21

wound on a shared core are respectively connected in series to two upper and lower horizontal deflection coils

23

and

25

. The pair of coils have a strong magnetic connection since they share the core.

In the deflection yoke

27

having such a construction as described above, the coils

21

connected in series to the two upper and lower horizontal deflection coils

23

and

25

have high inductance values only for induction current generated by a variation of the magnetic field of the raster rotation coil.

For example, if triangular wave current flows through the raster rotation coil

11

, then induction current flows in the deflection coils. The induction current is suppressed by the coils

21

connected in series to the upper side horizontal deflection coil

23

and the lower side horizontal deflection coil

25

.

Consequently, little influence is on the deflection current flowing in the circuitry of the receiver, and only the induction current induced by a variation of the magnetic field of the raster rotation coil is suppressed and the variation of convergence can be reduced. Since the coils

21

have a function of suppressing induction current, they are called induction current suppressing coils.

However, a series connection of such two coils having a strong magnetic connection as described above to upper and lower horizontal deflection coils gives rise to a new problem. In particular, if a vertical assembly error remains between a cathode ray tube and a deflection yoke, then this causes vertical asymmetry between an electron beam of the cathode ray tube and a horizontal deflection magnetic field. For example, if the horizontal deflection magnetic field is displaced downwardly with respect to the electron beam as shown in

FIG. 4A

, then misconvergence as shown in

FIG. 4B

appears on the screen.

As a popular method of correcting the misconvergence, variable coils are connected in series to upper and lower side deflection coils as shown in FIG.

4

C. The variable coils are used in order to adjust the balance in inductance value, and therefore called balance coils.

If the inductance value of a balance coil increases, then the current flowing therethrough decreases, but if the inductance value decreases, then the current increases. By adjustment of the balance coils, a difference can be provided between the amounts of deflection current to be supplied to the upper and lower side horizontal deflection coils.

Vertical asymmetry of the magnetic field can be adjusted by the difference in current. Accordingly, vertical asymmetry of the deflection current can be corrected as shown in

FIG. 4D

, and the misconvergence illustrated in

FIG. 4B

can be corrected.

However, in the circuit shown in

FIG. 3

, the induction current suppressing coils

21

connected in series between the upper and lower side horizontal deflection coils and the upper and lower side balance coils have a strong magnetic connection and are connected in the opposite phases to each other.

Therefore, even if it is tried to adjust the current between the upper and lower side horizontal deflection coils, the induction current suppressing coils

21

act to cancel current variations of the upper and lower side horizontal deflection coils.

Accordingly, for a deflection yoke for which a coil for suppressing induction current is mounted, the method of correcting misconvergence using balance coils which are used popularly cannot be used.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a deflection yoke which can simultaneously achieve correction of raster distortion by supplying current of an arbitrary period to a raster rotation coil and correction of misconvergence by producing a difference in current between upper and lower side horizontal deflection coils.

A deflection yoke according to the present invention includes a pair of saddle type horizontal deflection coils and a pair of saddle type or troidal type vertical deflection coils and further includes an annular raster rotation coil centered at an axis of a cathode ray tube and provided on the front side of the deflection yoke.

A pair of coils are respectively connected in series to the upper side horizontal deflection coil and the lower side horizontal deflection coil. The pair of coils are wound on a shared core and connected to the horizontal deflection coils such that the polarities of the coils may be opposite to each other. Consequently, the pair of coils have a strong magnetic connection. Preferably, the coupling coefficient of the pair of coils is as high as possible.

Further, a single bias coil is wound on the core on which the pair of coils are wound. Part of the horizontal deflection current flows through the bias coil.

The deflection yoke of the present invention is characterized in that a difference in current flowing through the upper side horizontal deflection coil and the lower side horizontal deflection coil is produced with the current which flows through the bias coil.

With the deflection yoke, if part of the horizontal deflection current flows into the bias coil, then this tends to generate magnetic fluxes inside the core of the pair of coils. At this time, induction current flows in the pair of coils having a strong magnetic connection so that the magnetic fluxes inside the core of the pair of coils may be cancelled. The induction current varies the balance between the deflection current flowing through the upper side horizontal deflection coil and the current flowing through the lower side horizontal deflecting coil. Consequently, a difference is produced between the current which flows through the upper side horizontal deflection coil and the current which flows through the lower side horizontal deflection coil.

Accordingly, by adjusting the current to be supplied to the bias coil, misconvergence arising from vertical asymmetry of the horizontal deflection magnetic fields can be corrected.

In order to adjust the current to be supplied to the bias coil, a bridge circuit which includes four inductors can be used. An input terminal of bridge circuit is connected to the low voltage sides of the horizontal deflection coils. Accordingly, as input current, horizontal deflection current flows. A pair of output terminals of the bridge circuit are connected to the bias coil. The balance of the bridge circuit depends upon the values of the four inductors, and the amount and the direction of current flowing through the bias coil depend upon the balance.

If the four inductors are variable inductors, the inductance values of them can be adjusted freely. The amount and the direction of current to flow through the bias coil can be adjusted by adjustment of the variable inductors. Accordingly, the correction amount and the polarity of misconvergence can be adjusted.

It is also possible to use a non-linear inductor for the bridge circuit. For example, if a fixed bias magnetic field with a permanent magnet is applied to a coil, the inductance value of the coil indicates non-linearity. An inductor of the type just described is called a saturable reactor.

Where a non-linear inductor is used, operation of the bridge circuit varies depending upon the direction and the magnitude of the horizontal deflection current.

Alternatively, an inductor whose bias magnetic field varies in response to the vertical deflection current may be used for the bridge circuit. In this instance, of the bridge circuit varies also in response to the direction and the magnitude of the vertical deflection current.

Where a non-linear inductor is used in this manner, a correction pattern of misconvergence can be operated within a fixed range.

The current to be supplied to the bias coil need not always be part of the deflection current. For example, a circuit for driving the bias coil may be provided in a receiver such that current is supplied from the circuit to the bias coil.

In the deflection yoke just described, current of an arbitrary waveform can be supplied to the bias coil. Accordingly, the balance in current between the upper side horizontal deflection coil and the lower side horizontal deflection coil can be varied arbitrarily.

The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective view showing a conventional deflection yoke;

FIG. 2

is a side elevational view showing coils and a core of the deflection yoke of

FIG. 1

;

FIG. 3

is a connection diagram of a conventional deflection yoke;

FIG. 4A

is a diagrammatic view illustrating a manner wherein horizontal deflection magnetic fields generated from horizontal deflection coils are displaced downwardly with respect to an electron beam;

FIG. 4B

is a diagrammatic view illustrating misconvergence generated when horizontal deflection magnetic fields are displaced downwardly;

FIG. 4C

is a connection diagram showing a connection of upper and lower side horizontal deflection coils and balance coils;

FIG. 4D

is a diagrammatic view illustrating a manner wherein displacement of horizontal deflection magnetic fields are modified by an action of the balance coils;

FIG. 5

is a connection diagram showing a first embodiment of a deflection yoke according to the present invention;

FIG. 6

is a schematic view showing an appearance of an induction current suppression coil used in the deflection yoke of

FIG. 4

;

FIG. 7A

is a connection diagram showing an example of a high impedance connection of induction current suppression coils employed in the deflection yoke of

FIG. 4

;

FIG. 7B

is a connection diagram showing an example of a low impedance connection of the induction current suppression coils employed in the deflection yoke of

FIG. 4

;

FIG. 8

is a connection diagram showing a first modification to the first embodiment of the deflection yoke according to the present invention;

FIG. 9A

is a waveform diagram showing deflection current flowing in the circuit of the first modification in the form of a current variation amount with respect to time;

FIG. 9B

is a waveform diagram showing current flowing in a bias coil of the circuit of the first modification in the form of a current variation amount with respect to time;

FIG. 10

a diagrammatic view showing an XV misconvergence pattern which appears on a screen of a cathode ray tube;

FIG. 11

is a connection diagram showing a second modification to the first embodiment of the deflection yoke according to the present invention;

FIG. 12A

is a waveform diagram showing deflection current flowing in the circuit of the second modification in the form of a current variation amount with respect to time;

FIG. 12B

is a waveform diagram showing current flowing in a bias coil of the circuit of the second modification in the form of a current variation amount with respect to time;

FIG. 12C

is a waveform diagram showing vertical deflection current with which bias magnetic fields are generated from coils of a bridge circuit of the circuit of the second modification in the form of a current variation amount with respect to time;

FIG. 13

is a diagrammatic view showing a PQV misconvergence pattern which appears on a screen of a cathode ray tube; and

FIG. 14

is a connection diagram showing a second embodiment of the deflection yoke according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to

FIGS. 5

to

7

A and

7

B, there is shown a first embodiment of a deflection yoke according to the present invention. The deflection yoke

41

according to the present embodiment includes an induction current suppression coil

43

shown in

FIG. 6

for suppressing induction current generated inside horizontal deflection coils. The induction current suppression coil

43

includes two stranded wires

47

and

49

wound commonly on a ring-shaped core

45

(for example, a ferrite core) of a diameter of approximately 10 to 30 mm. Each of the stranded wires

47

and

49

is composed of seven wires of a diameter of approximately 0.15 mm. The number of turns of each of the stranded wires

47

and

49

is approximately 5 to 20 turns. The specifications of the wire materials, numbers of turns and so forth of the core

45

and stranded wires

47

and

49

depend upon conditions in which the deflection yoke is used.

In the induction current suppression coil

43

, if terminals T

1

, T

2

, T

3

and T

4

of a pair of coils

51

and

53

are connected in such a manner as shown in

FIG. 7A

, then magnetic fluxes inside the core

45

are generated in the same direction from the pair of coils

51

and

53

.

Accordingly, the inductance values of the pair of coils

51

and

53

are such high values as approximately 0.5 to 3 mH.

If the terminals T

1

and T

4

and the terminals T

3

and T

2

on the opposite sides of the pair of coils

51

and

53

are connected to each other as shown in

FIG. 7B

, then magnetic fluxes generated inside the core

45

are directed opposite to each other. Accordingly, the inductance values of the pair of coils

51

and

53

are such low values as approximately 1 μH or less.

A bias coil

55

of approximately 2 to 6 turns is wound around the core

45

of the induction current suppression coil

43

. The opposite ends of the bias coil

55

are connected to terminals T

5

and T

6

.

In the deflection yoke

41

, the induction current suppression coil

43

is connected to horizontal deflection coils with such a connection as shown in FIG.

5

. The deflection yoke

41

includes a pair of saddle type horizontal deflection coils (upper side horizontal deflection coil

57

and lower side horizontal deflection coil

59

) shown in FIG.

5

. Further, an annular (circular, polygonal or the like) raster rotation coil not shown is mounted on the front side of the deflection yoke in such a manner as to be centered at an axis of a cathode ray tube.

The upper side horizontal deflection coil

57

and the lower side horizontal deflection coil

59

are connected at one ends thereof to each other. The other end of the upper side horizontal deflection coil

57

is connected to the terminal T

1

of the coil

51

. The other end of the lower side horizontal deflection coil

59

is connected to the terminal T

4

of the coil

53

. The coils

51

and

53

have inductance values of approximately 4 to 20 times the inductance values of the horizontal deflection coils, and the polarities thereof are opposite in phase to each other. The terminal T

3

of the coil

51

and the terminal T

2

of the coil

53

are connected to a bridge circuit

61

.

The bridge circuit

61

includes a parallel connection of a pair of variable inductors

61

A and

61

B connected in series and another pair of variable inductors

61

C and

61

D connected in series similarly. The bridge circuit

61

has a pair of input terminals and a pair of output terminals. One of the input terminals, that is, the junction of the variable inductors

61

A and

61

C, is connected to the terminals T

3

and T

2

of the coils

51

and

53

while the other input terminal, that is, the junction between the variable inductors

61

B and

61

D, is connected to a leakage magnetic field cancellation coil

63

. The cancellation coil

63

is used to cancel a magnetic field leaking to the outside of the receiver. Meanwhile, one of the output terminals, that is, the junction between the variable inductors

61

A and

61

B, is connected to the terminal T

6

of the bias coil

55

while the other output terminal, that is, the junction between the variable inductors

61

C and

61

D, is connected to the terminal T

5

of the bias coil

55

.

Accordingly, since the bridge circuit

61

is formed from the variable inductors

61

A,

61

B,

61

C and

61

D, current flows in any direction through the bias coil

55

.

Now, the operation of the deflection yoke

41

having the construction described above is described.

When the inductance values of the bridge circuit

61

are in a balanced condition so that no current may flow through the bias coil

55

, current flows through the coils

51

and

53

so that the balance of the magnetic fields in the core

45

may be maintained. Usually, since the coils

51

and

53

are wound in an equal number of turns, also the current flowing through the coils

51

and

53

is equal.

When horizontal deflection current flows through the coils

51

and

53

, the magnetic fields generated from the coils

51

and

53

cancel each other. Accordingly, the induction current suppression coil

43

acts as a resistor which has little inductance. The resistance value of the induction current suppression coil

43

is sufficiently low because the number of turns of the coil is small. Accordingly, the resistance value can be ignored practically. On the other hand, induction current induced by an influence of the raster rotation coil flows in such a manner as to circulate in a closed loop which includes the horizontal deflection coils

57

and

59

. Accordingly, the magnetic fields generated from the coils

51

and

53

overlap each other, and the induction current suppression coil

43

has a high inductance value. Accordingly, the coil

43

suppresses flow of the induction current. In other words, the induction current suppression coil

43

suppresses only induction current generated by an influence of the raster rotation coil without having an influence on the deflection current at all.

Here, if the variable inductors

61

A,

61

B,

61

C and

61

D of the bridge circuit

61

are varied, then the balance of the bridge circuit

61

varies, and part of the horizontal deflection current flows into the bias coil

55

. Consequently, the bias coil

55

tends to generate magnetic fluxes inside the core

45

of the induction current suppression coil

43

. At this time, in the induction current suppression coil

43

, induction current flows in a direction in which it prevents generation of magnetic fluxes inside the core

45

. In other words, induction current is generated in the coils

51

and

53

.

The induction current flows circulating the closed circuit including the deflection coils

57

and

59

. Consequently, the induction current flows in the same direction as that of the deflection current in either one of the upper side horizontal deflection coil

57

and the lower side horizontal deflection coil

59

, but flows in the opposite direction to that of the deflection current in the other side of them.

Consequently, the induction current varies the balance of the current flowing through the deflection coils

57

and

59

.

Consequently, the balance of the magnetic fields generated from the upper side horizontal deflection coil

57

and the lower side horizontal deflection coil

59

varies. As a result, to suppress the induction current generated by an influence of the raster rotation coil and to vary the balance of the deflection current to correct misconvergence can be achieved simultaneously.

Next, a first modification and a second modification to the deflection yoke described above will be described.

Referring first to

FIGS. 8

to

10

, a deflection yoke

69

according to the first modification uses a bridge circuit

71

in place of the bridge circuit

61

described above. The bridge circuit

71

includes saturable reactors

73

a

and

73

d

in place of the variable inductors

61

A and

61

D (refer to

FIG. 5

) which are components of the bridge circuit

61

. Each of the saturable reactors

73

a

and

73

d

is composed of an inductor

75

and a permanent magnet

77

.

If the magnitude and the direction of current flowing through the inductor

75

vary, the inductance value of the saturable reactor varies non-linearly.

The construction of the remaining part of the deflection yoke

69

is similar to that of the deflection yoke

41

described above.

With the present deflection yoke

69

, the balance of the bridge circuit

71

varies in response to the magnitude and the direction of the horizontal deflection current by means of the saturable reactors

73

A and

73

D. Consequently, parabolic current can be generated in the bridge circuit

71

. When current of a waveform shown in

FIG. 9B

is supplied to the bias coil

55

, the horizontal deflection current becomes that having a waveform shown in FIG.

9

A. Consequently, correction of misconvergence called XV illustrated in

FIG. 10

is allowed.

Referring now to

FIGS. 11

to

13

, there is shown a deflection yoke

79

according to the second modification to the first embodiment of the deflection yoke according to the present invention. With the deflection yoke

79

according to the modification

2

, a bridge circuit

81

is used in place of the bridge circuit

61

described above. The bridge circuit

81

includes saturable reactors

83

B and

83

D in place of the variable inductors

61

B and

61

D (refer to

FIG. 5

) which are components of the bridge circuit

61

. Each of the saturable reactors

83

B and

83

D includes an inductor

85

and a permanent magnet

87

, and vertical deflection current is supplied to coils

88

A and

88

B to apply bias magnetic fields to the saturable reactors

83

B and

83

D. The construction of the remaining part of the deflection yoke

79

is similar to that of the deflection yoke

41

described above.

With the present deflection yoke

79

, the inductance values of the saturable reactors

83

b

and

83

d

are modulated with vertical deflection current of a waveform shown in FIG.

12

C. Consequently, the balance of the bridge circuit

81

varies in response to the magnitude and the direction of the vertical deflection current. Accordingly, current of a waveform shown in

FIG. 12B

can be supplied from the bridge circuit

81

to the bias coil

55

to correct the waveform of the deflection current to that shown in FIG.

12

A. Consequently, correction of misconvergence called PQV illustrated in

FIG. 13

is allowed.

Now, a second embodiment of a deflection yoke according to the present invention is described with reference to FIG.

14

. In the deflection yoke

89

according to the present second embodiment, the bridge circuit

61

shown in

FIG. 5

is omitted, and the terminals T

3

and T

2

of the coils

51

and

53

are connected to each other, and a leakage magnetic field cancellation coil

63

is connected to the junction of the terminals T

3

and T

2

. Further, a bias coil

55

is provided for the core

45

in a similar manner as described above. To the bias coil

55

, current, for example, of a waveform similar to that shown in

FIG. 9A

described above or a waveform shown in

FIG. 12B

obtained by composing arbitrary currents which vary in periods of horizontal scanning and vertical scanning by means of a circuit inside a receiver for which a cathode ray tube is used. In short, by supplying current from the outside of the deflection yoke to the bias coil

55

, arbitrary asymmetrical currents can be supplied to the upper side horizontal deflection coil

57

and the lower side horizontal deflection coil

59

.

With the deflection yoke

89

, magnetic fluxes can be generated inside the core

45

of the induction current suppression coil

43

with the composed current to vary the balance of the currents flowing through the upper side horizontal deflection coil

57

and the lower side horizontal deflection coil

59

. As a result, the waveform can be adjusted freely in accordance with the characteristic of the cathode ray tube or the deflection yoke to perform misconvergence correction readily without using an expensive saturable reactor.

It is to be noted that, while it is described that the induction current suppression coils connected to the horizontal deflection coils of each of the deflection coils

41

,

69

,

79

and

89

described above is constructed such that a stranded wire is wound on a core of a ring shape, the coil is not limited to this and may include a C-shaped or E-shaped core. Further, where heat generation by eddy current does not matter, a solid wire may be used for the coil.

Further, it is described that one of two input terminals of each of the bridge circuits

61

,

71

and

81

is connected to a leakage magnetic field cancellation coil. However, where a leakage magnetic field to the outside of a receiver does not matter, the cancellation coil may be omitted. In this instance, the input terminal is connected directly to a deflection circuit of the receiver.

As described in detail above, suppression of induction current induced from a raster rotation coil and correction of misconvergence performed by producing a difference in current between an upper side horizontal deflection coil and a lower side horizontal deflection coil can be achieved simultaneously.

Further, by supplying current to be supplied to a bias coil as current of an arbitrary waveform from the outside of the deflection yoke, a waveform can be adjusted freely to perform misconvergence correction readily without using an expensive saturable reactor.

While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

Number	Name	Date
5250876	Van Mierlo et al.	Oct 1993
5598055	Inoue et al.	Jan 1997
5945779	Inoue et al.	Aug 1999

Deflection yoke for color cathode ray tube

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (3)