US3662307A - Flyback transformer - Google Patents

Abstract

Temperature increase becomes a problem with a flyback transformer of a television receiver since it handles a high voltage. In order to cope with this, it has conventionally been the usual practice to make the core gap sufficiently great to provide allowance for the design. With such a construction, however, the transformer becomes large in size, and the highvoltage stability thereof is deteriorated. In view of this, in accordance with the present invention, a temperature-sensitive ferrite is provided in the gap of the core to prevent the slope of the B-H curve from becoming unduly small and to stabilize the high voltage during normal operation. In case the temperature is increased, the Curie point of this temperature-sensitive ferrite is utilized to improve the temperature stability of the flyback transformer.

Description

[ 1 May 9,1972

[54] FLYBACK TRANSFORMER [72] Inventors: Teruhiro Tsukuda, Moriguchi-shi; Takashi Tsutsumi, Suita-shi, both of Japan Matsushita Electric Co., Ltd., Osaka, Japan [22] Filed: Dec. 10, 1969 [21] Appl.No.: 883,806

[73] Assignee:

FOREIGN PATENTS OR APPLICATIONS 1,005,293 12/1951 France ..336/l78 Primary Examiner- Thomas J. Kozma Altome vStevens, Davis, Miller & Mosher [57] ABSTRACT Temperature increase becomes a problem with a flyback transformer of a television receiver since it handles a high voltage. In order to cope with this, it has conventionally been the usual practice to make the core gap sufficiently great to provide allowance for the design. With such a construction, however, the transformer becomes large in size, and the highvoltage stability thereof is deteriorated. In view of this, in accordance with the present invention, a temperature-sensitive ferrite is provided in the gap of the core to prevent the slope of the B-H curve from becoming unduly small and to stabilize the high voltage during normal operation. In case the temperature is increased, the Curie point of this temperature-sensitive ferrite is utilized to improve the temperature stability of the flyback transformer.

3 Claims, 9 Drawing Figures P ATENTEDHAY 91912 1 3,662,307

SHEET 1 BF 3 PRIOR ART 1 /6 PRIOR ART MAGNET/C FLUX 05/vs/rY B MAGNET/Z/IVG FOPCE H CORE GAP /00?) I NVENTORS.

TERUHIRO TSUKUDA TAKASHI TSUTSUMI TTORNEYS PATENTEDMAY 9 I972 SHEET 2 BF 3 MdGA/EUZ/IVG' FGPCEH INVENTORS TERUHIRO 'TSUKUDA TAKASHI TSUTSUMI v TTORNEYS FLYBACK TRANSFORMER This invention relates to a flyback transformer for television receivers which is adapted to provide a high voltage that is stabilized with respect to temperature variations.

Generally, in a television receiver, the high acceleration voltage imparted to the picture tube is taken from the flyback transformer, but temperature rise becomes a problem with the flyback transfonner since the latter handles high power. A large temperature rise can occur especially if the AC input voltage becomes excessive or the horizontal oscillator frequency is deviated so as to be lower than 15.75 KC. In order to eliminate such a drawback, it has heretofore been the usual practice to use a large core provided with a sufficient gap to allow for the design.

Further, a color television receiver which consumes high power requires a large-sized flyback transformer in the horizontal deflection output portion thereof, wherein since high power is handled, it is essential to stabilize the high voltage so as to minimize variations in the picture amplitude, beam convergence peculiar to shadow-mask type picture tubes, white balance, color purity and so forth. This high voltage is as high as about KV, and yet a capacity of 1 mA is required. In order to stabilize such a high voltage, there has been proposed a shunt regulator system in which a voltage regulator tube is inserted in parallel with the high voltage circuit and the feedback regulator system, a pulse amplitude induced in the secondary winding of the flyback transformer due to variations of the high voltage appearing in the flyback transformer being detected by a varistor or the like and then fed back to the horizontal output tube. However, these systems are disadvantageous because they require a large number of circuit elements.

FIG. 1 shows the construction of a common flyback transformer, wherein numeral 1 represents a ferrite core, 2 a gap, 3 a primary coil, and 4 a high voltage coil. By changing the gap 2 in accordance with the saturation type B-H curve with a hysteresis of the ferrite core as shown in FIG. 2, there are obtained B-H curves representing various values of a. From this, it will be seen that it is possible to obtain a curve with a lower value of p. by making the gap 2 greater.

In the conventional flyback transformer, the gap 2 is made so great that even if a load is increased, the operating point may be located in the straight portion of a 8-H curve. This is to prevent the temperature of the core from being increased due to an increase of the high voltage which results from the fact that when the transformer is operated in the neighborhood of the saturation point, is decreased by an increase of the load. With such an arrangement, however, the efficiency becomes low in the normal operating temperature range. (The permeability of the magnetic circuit is low.) Furthermore, in order to achieve a predetermined inductance, a great number of turns is required which makes the transformer'bulky. Still furthermore, in case the horizontal oscillation frequency is deviated to be lower or the transformer is used in a place where the ambient temperature is high, when there is provided a high AC input voltage, it is dangerous to use the transformer in the neighborhood of the saturation point. In such cases, therefore, the transformer could not be used. Another disadvantage is that a further increase of the gap deteriorates the high voltage stability as shown in FIG. 3.

The present invention is intended to eliminate the aforementioned drawbacks.

It is an object of the present invention to provide a flyback transformer having a temperature-sensitive ferrite inserted in a portion of the core, thereby eliminating a number of circuit elements which have conventionally been required for stabilizing the high voltage.

Another object of the present invention is to provide a flyback transformer which is stabilized with respect to temperature rise in the case of anomalous operation of the television receiver.

Still another object of the present invention is to provide a flyback transformer wherein a temperature-sensitive ferrite can be easily and rigidly mounted.

Other objects, features and advantages of the present invention will become obvious from the followingdescription taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view showing a conventional flyback transformer;

FIG. 2 is a view showing B-I-I curves thereof;

FIG. 3 is a view showing the relationship between the gap of the core and the internal resistance of the flyback transformer (the lower the internal resistance, the higher the stability);

FIG. 4 is a side view showing the flyback transformer according to an embodiment of the present invention;

FIG. 5 is a view showing an approximate B-H curve of the flyback transfonner of FIG. 4;

FIG. 6 is a view showing the 8-H curves of the flyback transfonner in terms of the thickness and characteristics of the temperature-sensitive ferrite;

FIG. 7 is a view showing curves representing the effect of the temperature-sensitive ferrite in terms of temperature variations; and

FIGS. 8 and 9 are views showing how to mount the temperature-sensitive ferrite in the flyback transformer embodying the present invention by way of example.

Referring to FIG. 4, numerals l to 4 represent a core, gap, primary coil and high voltage coil respectively, which are similar to those of the conventional flyback transformers. In accordance with the present invention, a temperature-sensitive ferrite member 5 utilizing the Curie point is inserted in the gap 2 instead of making the latter great as in the prior art. This temperature-sensitive ferrite member 5 is made of a ferrite which is ferromagnetic in an ambient temperature range but loses its magnetic property, so as to become paramagnetic when a predetermined temperature is reached. This material is provided in the portion of the gap 2, and the transformer is normally operated in the vicinity of the saturation point as shown in FIG. 5, thereby improving the high voltage stability. This compensates for a decrease of the high voltage which stems from the fact that p. is decreased due to an increase of the load so that the anode current of the picture tube is increased. Thus, the high voltage stability is improved. Furthermore, in such an anomalous state that the horizontal frequency is deviated for a high AC input voltage, if the ambient temperature is increased, then the temperature of the ferrite is also increased so that it becomes paramagnetic. This is equivalent to an increase of the gap 2. Thus, it is possible to prevent the temperature of the flyback transformer from being elevatedhThe use of a core provided with a stepped gap results in such B-I-I characteristics as shown in FIG. 5. By providing atemperature-sensitive ferrite in this gap portion, a flyback transformer can be obtained which provides high voltage stability for a high AC input voltage when the ambient temperature is high, thereby making it possible to improve the performance of a television receiver.

FIG. 6 shows B-I-I curves in terms of an air gap and temperature-sensitive magnetic material. As will be seen from this Figure, the curve for the case where the gap is zero rapidly becomes saturated, so that p. is remarkably decreased when the operating point is varied, so that L is decreased, resulting in abnormal operation of the flyback transformer. It will also be seen that for an increased gap, the permeability p. remains substantially unchanged even if the operation point is changed, which makes no contribution to the high voltage stability, and that when the temperature sensitive ferrite is inserted, there is a point where p. is suitably varied. Referring to FIG. 7, there are shown B-H curves for the cases where a temperature-sensitive ferrite is inserted and those for the cases where no such ferrite is inserted, taking ambient temperature as a parameter. As will be seen from this Figure, in the absence of the temperature-sensitive ferrite, as theambient temperature increases, the saturation of the B-H curve becomes remarkably so that u is markedly decreased with a result that L is changed. Consequently, the high voltage generating circuit is brought into an anomalous operating state.

Description will now be made of the manner in which the temperature-sensitive ferrite is mounted. As shown in FIG. 8, a temperaturesensitive ferrite 6 may be inserted in a recess 7 formed in a core 8. Alternatively, a temperature-sensitive ferrite 9 may be fitted in a groove 11 formed in a core 10. By making the thickness of temperature-sensitive ferrite slightly smaller than the depth of the groove or recess fonned in the core, it is possible to prevent the ferrite from being damaged since no pressure is imparted thereto when the core is tightened. In this case, the temperature stability of the flyback transformer with respect to the anomalous operation is more or less deteriorated, but this constitutes no practical problem. An optimum high voltage stability point can be obtained by suitably selecting the depth of the groove or recess formed in the ferrite core, the thickness of the temperature-sensitive ferrite and its permeability value.

What is claimed is:

l. A flyback transformer having a ferrite core formed with an air gap and primary and secondary coils wound on said ferrite core for producing a high voltage in a television receiver, wherein the improvement comprises a temperature-sensitive ferrite inserted in said air gap which becomes rapidly paramagnetic when the temperature of said ferrite is increased beyond a predetermined value, said flyback transformer having a relatively low magnetic reluctance at temperatures below said predetermined value and remaining unsaturated at temperatures above said value thereby preventing excessive temperature rise.

2. A flyback transformer having a ferrite core formed with an air gap and primary and secondary coils wound on said ferrite core for producing a high voltage in a television receiver, wherein the improvement comprises a temperature-sensitive ferrite disposed in engagement with a recess formed in said air gap with a configuration similar to said temperature-sensitive ferrite, said ferrite becoming rapidly paramagnetic when the temperature of said ferrite is increased beyond a predetermined value, said flyback transformer having a relatively low magnetic reluctance at temperatures below said predetermined value and remaining unsaturated at temperatures above said value thereby preventing excessive temperature rise.

3. A flyback transformer as defined by claim 1 wherein said temperature sensitive ferrite becomes rapidly paramagnetic when a predetermined temperature is reached.

mg l g UN'I'FEDiS'lA'JE S PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo; 3,662,307 Dated May 9. 19 72- j Teruhirb TSUKUDA et a1.

It iscertified that error appears in the above-ddenrified patent and that said Letters Patent are hereby corrected as shown below:

I The correct name' of the Assignee should read I I Matsfishita Electric Industrial Co. Ltd

Signed and sealed this 3rd day 0f April 1973 (SEAL) 'Attest: v

EDWARD M. FLETCHER,JR. ROBERT GOT TSCHALK Attesting Officer Commissioner of Patents 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIOII Patent No. 3,662,307 Dated, May 9, 19.72

lnvcmofls) Teruhir'o TSUKUDA et a1 It iscertified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The correct name' of the Assignee should read I Matsfishita Electric Industrial Co. Ltd

Signed and-sealed this 3rd day of April 19 73.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOT TSCHALK Attesting Officer Commissioner of Patents

Claims (3)

1. A flyback transformer having a ferrite core formed with an air gap and primary and secondary coils wound on said ferrite core for producing a high voltage in a television receiver, wherein the improvement comprises a temperature-sensitive ferrite inserted in said air gap which becomes rapidly paramagnetic when the temperature of said ferrite is increased beyond a predetermined value, said flyback transformer having a relatively low magnetic reluctance at temperatures below said predetermined value and remaining unsaturated at temperatures above said value thereby preventing excessive temperature rise.

2. A flyback transformer having a ferrite core formed with an air gap and primary and secondary coils wound on said ferrite core for producing a high voltage in a television receiver, wherein the improvement comprises a temperature-sensitive ferrite disposed in engagement with a recess formed in said air gap with a configuration similar to said temperature-sensitive ferrite, said ferrite becoming rapidly paramagnetic when the temperature of said ferrite is increased beyond a predetermined value, said flybaCk transformer having a relatively low magnetic reluctance at temperatures below said predetermined value and remaining unsaturated at temperatures above said value thereby preventing excessive temperature rise.

3. A flyback transformer as defined by claim 1 wherein said temperature sensitive ferrite becomes rapidly paramagnetic when a predetermined temperature is reached.

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