JPS6122847B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flyback transformer for a television receiver, and its object is to prevent ringing, which appears as vertical stripes of brightness and darkness on a cathode ray tube screen, and to obtain high-quality images. .

The high voltage coil on the secondary side of the flyback transformer has a very large number of turns in order to obtain a high step-up ratio.
Moreover, since the voltage is high, the coil must be wound with an insulating distance from the output coil on the primary side, so leakage inductance and distributed capacitance cannot be ignored. These resonant circuits generate harmonics of the flyback pulse, and a complex ringing waveform is superimposed on the flyback pulse. Since this ringing persists not only during the retrace period but also during the scanning line period, it is transmitted through various paths by capacitive coupling or electromagnetic coupling, and is mixed into the video circuit as ringing noise, which is characteristic of the screen of a cathode ray tube. Generates a vertical striped pattern of light and dark. In order to suppress the deterioration of image quality due to this ringing, various measures have been taken since then. For example, in order to reduce the ringing of the flyback transformer itself, fine adjustments are made to the harmonic distribution and its Q, and in order to suppress the transmission of ringing, a shielding case is used, or printed circuits and lead wires are used. Measures have been taken to improve the wiring, but all of these require a great deal of time and effort for design and adjustment.

The present invention provides a flyback transformer with significantly improved ringing effects, and its basic idea is to combine a relatively low-frequency fundamental pulse (approximately 40 KHz) flowing through a high-voltage coil with an extremely high-frequency ringing. Focusing on the difference in frequency (approximately 100KHz to 1MHz), the method uses the fact that the impedance of a capacitor is inversely proportional to the frequency to selectively remove only the ringing. Specifically, a conductor is provided close to the high-voltage coil, and the ringing current is guided to this conductor via distributed capacitance between the high-voltage coil and the ringing current, which is passed through a predetermined resistance to cause power loss and attenuate the ringing. It should be done quickly.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic cross-sectional view of an embodiment of the flyback transformer of the present invention. In the figure, reference numeral 1 denotes a magnetic core, on one leg of which a primary output coil 2 is attached, and around it is provided a collar bobbin 3, on which a high voltage coil 4 is wound in parts. A rectifier diode 5 is connected to the high voltage end of the high voltage coil 4, and a thin conductor 6 is provided between the high voltage coil 4 and the output coil 2. This conductor 6 is provided in a cylindrical shape concentric with the core 1, but if it goes around completely in a cylindrical shape and its both ends touch, it will form a secondary side short circuit, so the both ends should be spaced a little apart. Either separate the terminals from each other, or insulate the terminals so that they do not touch each other to prevent short circuits. This conductor 6 is connected to the low voltage end of the high voltage coil 4 via a resistor 7.

Next, the operation of this flyback transformer against ringing will be explained. When a sawtooth wave current flows through the output coil 2, a flyback pulse is induced in the high voltage coil 4. In this embodiment, positive alternating current pulses are generated in all parts of the divided high-voltage coil. A ringing current is superimposed on this positive pulse. On the other hand, since the conductor 6 is connected to the low voltage side of the high voltage coil 4 via the resistor 7, it is always at a constant potential close to direct current. Therefore, in accordance with the ringing voltage superimposed on the high voltage coil, charge is stored in the distributed capacitance between the high voltage coil 4 and the conductor 6, and a ringing current flows through the resistor 7 due to the change in the charge. At that time, power consumption occurs in the resistor 7, and the ringing energy is consumed. Since the frequency of the harmonics that are the source of ringing is high as described above, the impedance of the distributed capacitance is sufficiently low, and the energy consumed in one ringing cycle is close to the initially applied ringing energy, so the ringing occurs quickly. attenuates to On the other hand, since the fundamental wave of the flyback pulse has a low frequency and the energy transmitted from the primary side to the secondary side is extremely large, almost no loss occurs. In this way, this flyback transformer has very little ringing.

In the embodiment described above, the conductor 6 is provided along the inner circumference of the high voltage coil 4;
A similar effect can be obtained by providing it on the outer periphery of a flyback transformer or on the outer periphery of a flyback transformer case. Further, in this embodiment, the diode 5 is connected to the high voltage end of the high voltage coil, but even if the diode 5 is connected to the low voltage end, all the pulses will be negative pulses, and the same result as in the above embodiment will be obtained. Effects can be obtained.

Furthermore, instead of the conductor 6, a resistor layer can be provided and connected directly to the high voltage coil 4, so that the resistor 7 can be omitted. In this case, since the higher the ringing voltage is in the part, the higher the resistance is connected in series, the ringing can be effectively reduced.

FIG. 2 shows another embodiment of the invention. In recent years, in order to reduce voltage fluctuations due to load fluctuations in high-voltage output voltage, a configuration has been adopted in which the high-voltage coil is divided into several pieces and these are connected in series via diodes, which equalizes the distributed capacitance of the high-voltage coil. It is widely practiced to reduce the harmonics and increase the order of the harmonics. In such a configuration, because of the distributed capacitance that each high-voltage coil has between the coil and the ground, a so-called neutral point is generated that is always at a DC potential. This neutral point occurs between each divided high-voltage coil, and when flyback pulses occur symmetrically in positive and negative directions around this point, ringing also occurs almost symmetrically.
The distributed capacitance between the high-voltage coil and the conductor placed close to it is charged at the part near the positive pulse and discharged at the part near the negative pulse. Since almost no loss occurs, ringing is difficult to attenuate. That is, in order to fully exhibit the effects of the present invention, it is desirable that the pulses generated in the high-voltage coil be mainly positive AC pulses or negative pulses. The embodiment shown in FIG. 2 is a schematic cross-sectional view when the present invention is applied to a flyback transformer in which the high voltage coil is divided by diodes.

In the embodiment of FIG. 2, the divided high voltage coil 4
Each of a to 4d is flatly wound around the output coil 2 in a concentric cylindrical shape, and the high voltage coils forming each layer are connected in series via a diode 5, and a diode is also connected to the high voltage end. Further, a conductor 6 similar to the embodiment shown in FIG. 1 is provided between the innermost layer 4a of the high voltage coil 4 and the output coil 2, and this is connected to the low voltage end of the high voltage coil via a resistor 7. .

In the flyback transformer constructed in this way, since the high voltage coil 4a, which has the lowest potential, has no diode at the low voltage end, the low voltage end becomes the neutral point of the DC potential, and only positive pulses are present. The second, third, and fourth high-voltage coils 4a to 4d are also affected by this pulse and produce almost only positive pulses. That is, in this flyback transformer, since only positive AC pulses are present in the high voltage coil, the ringing always has the same polarity. Therefore,
The distributed capacitance between adjacent conductors is charged and discharged simultaneously, and the current flows through the resistor 7 without being neutralized internally. In this way, ringing can be made extremely small, similar to the embodiment described with reference to FIG. In this embodiment as well, the conductor 6 may be provided on the outer periphery of the high voltage coil 4 or may be provided on the outer periphery of the case to obtain basically the same effect. Also, a resistor layer is provided in place of the conductor 6, and the resistor 7
can also be omitted.

As described above, according to the present invention, since the ringing of the flyback transformer is extremely small,
The design of the flyback transformer and the printed circuit of the television receiver are simplified, and effects such as less ringing influence on the screen and the ability to obtain high-quality images can be obtained.

Note that the resistance values of the resistor 7 and the resistive layer are as follows:
Approximately 100Ω to 10KΩ has a small overall power loss.
It has been experimentally confirmed that the ringing is well attenuated.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of one embodiment of a flyback transformer of the present invention, and FIG. 2 is a schematic cross-sectional diagram of another embodiment of the present invention. 1...Magnetic core, 2...Primary side output coil, 3
...Brim bobbin, 4...High voltage coil, 5...
Diode, 6...conductor, 7...resistance.

Claims (1)

[Claims] 1. Comprising a primary coil and a secondary high voltage coil,
A flyback transformer characterized in that a conductor is provided close to the high voltage coil, and the conductor is connected to the low voltage end of the high voltage coil via a resistor. 2. A flyback transformer characterized in that the conductor and resistor according to claim 1 are integrally formed of a conductor with a high resistance value.