KR930006939B1 - Flyback fransformer - Google Patents

Abstract

The plyback transformer for shielding electromagnetic wave comprises an upper and a lower ferrite core which are integrated with each other. As the length of side rack of the lower and the upper ferrite core (32)(34) is different, when the lower and the upper ferrite core are joined, void is formed at the inner of a case (10).

Description

Electromagnetic Shielding Flyback Transformer

1 is a diagram for explaining electromagnetic leakage in a typical flyback transformer.

2 is a state diagram of the ferrite core inside the flyback transformer for explaining the action of the ferrite core.

3 is a self-saturation curve.

4 is a ferrite core coupling structure of a conventional flyback transformer for preventing electromagnetic leakage.

5 is a structural diagram of a flyback transformer for explaining the present invention.

6 is a binding state of the ferrite core used in the flyback transformer of the present invention.

* Explanation of symbols for main parts of the drawings

10: case 16: clip

22 coil 32 upper ferrite core

34: lower ferrite core 36: void

38: sheet

The present invention relates to an electromagnetic shielding flyback transformer having an EMI (Electro Megnetic Interference) countermeasure.

The flyback transformer, which supplies high voltage to the CRT of the TV or monitor set, boosts the primary input pulse voltage to the secondary side through the ferrite core and rectifies it to generate DC high voltage.

Normally, the pulse voltage input to the primary coil is about 1000Vpp and the voltage induced by the secondary coil through the ferrite core is 20kV-30kV boosted 20-30 times. Some of the magnetic lines generated by the primary coil are ferrite cores. It does not flow inside but exists as a magnetic field that flows or propagates into the air, that is, a leakage magnetic field.

The leakage magnetic field causes electromagnetic interference (EMI) in the peripheral circuit. In the conventional flyback transformer, the leakage magnetic field is so strong that it affects the characteristics of the peripheral circuit and components, so that the CRT screen is unstable due to instability of the circuit constant. The property was markedly deteriorated.

The reason for the occurrence of such an EMI phenomenon will be described based on the structure of the conventional flyback transformer shown in FIG.

The flyback transformer is largely wound around the case 10 and respective high and low pressure bobbins (not shown), and passes through the input / output coil 22 installed inside the case and the bobbin of the input / output coil 22 to the outside. It consists of a ferrite core that is exposed and has a mating structure of the upper and lower cores 12 and 14 by the clip 16.

Here, the sheets 18 and 20 are inserted into the mating portions of the upper and lower ferrite cores 12 and 14 to form voids. Without the voids, the ferrite cores are easily saturated even with a small current, thereby supplying a large current. Almost all ferrite core structures meet these voids to give. On this point, more observation is made with reference to FIG. When the coil 22 is wound around the ferrite cores 12 and 14 to flow a current, magnetomotive force Vm is generated, and the unit is [AT].

When magnetic force is generated in the magnetic circuit, a magnetic flux (ø) flows inside the ferrite core, and there is a magnetic resistance (R) received as the magnetic flux flows.

The relation is Vm = øR.

The magnetoresistance R is proportional to the total length of the ferrite cores 12 and 14 (2l ₅ + 2l ₆ ) and inversely proportional to the cross-sectional area (S = 10 × 10 ⁻³ × 14 × 10 ⁻³ ), If the ferrite cores 12 and 14 are homogeneous isotropic (Μ: Permeability)

Therefore, when the gap 28 of the upper and lower ferrite cores 12 and 14 is 0.3 mm and the number of turns of the coil 22 is 100, the magnetic flux density at the center of the ferrite cores 12 and 14 is set to 200 Gauss. The current is calculated as follows. Now reactance in void 28, ie magnetoresistance R = Because of

R = (0.3 + 0.3) × 10 ^-3 / 4π × 10 ^-7 × (10 × 10 ^-3 ) × (14 × 10 ^-3 )

= 6 × 10 ^-4 / 4π × 10 ^-7 × 1.4 × 10 ^-4

= 0.34 × 10 ⁷ [AT / W _b ]

Where the air permeability μo is 4π × 10 ⁻⁷ AT / m and d is the pore length. However, the residual flux through the cross section of the void or ferrite core is the same

Since ø = BS, ø = 0.2 × (1.0 × 10 ^-2 × 1.4 × 10 ^-2 ) = 2.8 × 10 ^-5 [W _b ], and the magnetic force Vm = øR causing ø in the void

Vm = (0.34 × 10 ⁷ ) (2.8 × 10 ⁻⁵ ) = 95.2AT.

Therefore, in the magnetization curve of FIG. 3, the magnetization force of 100 AT / m is required for the ferrite cores 12 and 14 to have a magnetic flux density of 2000 gauss. At this time, the gap between the pores 28 is very small, so that the total length of the ferrite cores 12 and 14 is

= 4l ₁ + 2l ₅

≒ 2 (l ₆ + l ₅ )

= 2 (43 + 63)

= 0.212 [m]

Magnetic force Vm = 100AT x 0.212m = 21.2A T for causing magnetic flux ø to the ferrite core.

Thus, the electrical power is 116.4AT and the current is 1.16A. In addition, the magnetic permeability ratio between the ferrite core and air is 1000: 1. This leakage is caused by the magnetic flux.

As such, the magnetomotive force required at the pores 28 of the ferrite cores 12 and 14 eventually propagates to the outside in the form of leakage magnetic fluxes, resulting in heat loss.

In order to prevent the leakage flux, the voids need to be removed, but in the absence of voids, the magnetic flux saturation occurs even at a small current, so that the efficiency of the flyback transformer is significantly reduced. .

On the other hand, in the case of the flyback transformer as shown in FIG. 1, bulge waves 24 and 26 are generated in the voids formed by the sheets 18 and 20 at the mating portions of the upper and lower ferrite cores 12 and 14. Of these EMI waves, the unwanted waves (leakage flux) 24 in the voids formed by the sheet 18 are shielded by the case 10, but the unwanted waves 26 in the voids formed by the sheet 20 are external. It radiates in all directions, affecting adjacent parts and circuits.

As a method of reducing the propagation of the unwanted radio waves, as shown in FIG. 4, only the mating portions of the upper and lower ferrite cores 12 and 14 penetrating the hollows of the coil 22 inside the case 10. Inserting the sheet 18 to form a void, and a portion that is coupled to the outside of the case 10 has been proposed a method of fixing with the clip 16 as it is without a sheet for forming the void.

However, flux leakage problems exist with improved flyback transformers. That is, since the outer mating defects of the upper and lower ferrite cores 12 and 14 do not form a perfect coupling and have the slits 30, this is unnecessary wave propagation due to magnetic leakage in the remaining three directions except one direction ( 26) cannot be an effective EMI countermeasure.

The present invention proposes an electromagnetic shielding flyback transformer for EMI, which can effectively suppress the generation of unwanted waves in the conventional flyback transformer as described above.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

As shown in FIGS. 5 and 6, the flyback transformers of the present invention have different structures of the upper and lower ferrite cores 32 and 34 which are coupled to each other.

Specifically, the lengths l ₁₁ and l ₁₃ of both side racks of the upper ferrite core 32 are different from each other. The difference in length is to be 1/2 of the void. In addition, the lengths (l ₁₂ , l ₁₄ ) of both side racks of the lower ferrite core 34 are also different from each other by 1/2 of the gap.

Accordingly, when the upper and lower ferrite cores 32 and 34 are coupled to each other, the side racks ₁₁ and ₁₂ and the side racks ₁₃ and ₁₄ may be combined to match each other, and thus the short side racks as shown in FIG. At (l ₁₃ , l ₁ 4) a void 36 is formed.

If the side racks (l ₁₃ , l ₁₄ ) of the ferrite core in which the voids 36 are formed are inserted into the hollows of the coils 24 of the case 10, the voids are formed inside the case 10 as shown in FIG. In the outside, pores are not generated in the upper and lower ferrite cores 32 and 34.

5 shows that the voids formed by the ferrite core inside the case 10 are formed by the sheet 38. However, even if the sheet 38 is removed, the upper and lower ferrite cores 32 and 34 joining clips ( 16) the desired void can be obtained.

Therefore, the magnetic flux generated from the ferrite core flows through the center of the ferrite core by flowing a current through the coil 24. The upper and lower ferrite cores 32 and 34 are closely contacted with each other. Therefore, electromagnetic radiation does not occur here, and thus does not cause EMI interference to adjacent components or circuits.

On the other hand, in the air gap of the upper and lower ferrite cores 32 and 34 inside the case 10, an undesired wave 24, that is, electromagnetic waves are generated, but the electromagnetic waves are shielded by the wall of the case 10. It doesn't work.

As described above, the present invention exhibits a unique effect of effectively preventing electromagnetic leakage occurring in the flyback transformer through simple length deformation of the ferrite core structure for the flyback transformer.

Claims (1)

In a flyback transformer having a coupling structure of upper and lower ferrite cores, air gaps are formed in only one side of the upper and lower ferrite cores 32 and 34 that are positioned inside the case 10 when the side racks have different lengths. Electromagnetic turn flyback transformer, characterized in that formed.