JPH0483316A - Current transformer - Google Patents

Abstract

PURPOSE:To enable frequency and temperature to be stabilized and to be compact by forming a magnetic core with an amorphous magnetic material whose thickness is 70mum or less, which is in thin-band shape, and whose Curie temperature is 250 deg.C or higher. CONSTITUTION:A magnetic core is formed by an amorphous magnetic material whose thickness is 70mum or less, which is in thin-band shape, and whose Curie temperature is 250 deg.C or higher, thus achieving a current transformer which is stable in terms of frequency and temperature and a stable lighting operation when it is applied to an inverter lighting device. Further, the magnetic core can be made compact by allowing saturation flux density to be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current transformer applied to an inverter lighting device, a switching power supply, and the like.

[Conventional technology]

In inverter lighting devices and switching power supplies that switch at a relatively low frequency (approximately 20kF [z~IMHz)], the current transformer method detects the current in the main circuit or control circuit, and feeds back the control signal based on the detection signal. are widely adopted.

For example, in the inverter lighting device shown in Fig. 6, the lamp L
A current transformer CT is provided in series with the lamp L to detect the current flowing through the lamp L to detect the operating state of the lamp L, that is, the normal lighting state, dimmed lighting state, and abnormal lighting state, and controls the control circuit CON. In the figure, DR,
, DR2 is a drive circuit, Tr (, Tr 2 is nM
A switching element is an example of an Os transistor, and E is a power supply.

The current transformer used in such an inverter lighting device needs to have good sensitivity, but characteristics in the frequency range, temperature range, and current range in which it is used are important.

The 70th shows the principle of a current transformer, which detects the primary current 11 and outputs an output voltage 2. Secondary electric current i12. Primary winding N, secondary winding vAN2,
If the magnetizing force of the magnetic core is H, and the magnetic path length of the core is i, then from the relationship of the magnetomotive force, NI I, = H1 + N212 ......
(1) holds true. From this formula (11), H= (N, 1l-N212)z!...
(2), and if the permeability of the magnetic core is μ, then B−μH
From the relationship, B=μ(N111-\212)/I!・・・・・・・・・
(3) is obtained. On the other hand, the secondary voltage V2 is defined as the magnetic path cross-sectional area S of the magnetic core, V2=N2S (dB/d t)...
...Since it is given by (4), V2 = μ(S//2) −d(N, I, −
N 21 2 )/dt (5). From this equation (5), it can be seen that the secondary voltage V2 changes with the magnetic permeability μ of the magnetic core, and it can be seen that the larger the magnetic permeability μ is, the better the sensitivity is.

[Problem to be solved by the invention]

However, although ferrite has been used as a magnetic material for current transformers, there has been a problem in that detection sensitivity changes depending on temperature, making control difficult. That is, the temperature characteristics of magnetic permeability of conventional Mn-Zn ferrite (5B7C manufactured by Hitachi Ferrite) are as shown in FIG. 8, and vary greatly depending on temperature. For example, when the temperature is 40 degrees, the magnetic permeability decreases by about 30% at 10 degrees, and the detection voltage decreases in proportion to this.As described above, the conventional material ferrite has a drawback of poor temperature characteristics. In addition, various other ferrite materials were investigated, but although the numerical values were large and small, no significant improvement was found.

Therefore, an object of the present invention is to provide a current transformer with stable temperature characteristics.

[Means to solve the problem]

The current transformer of the present invention has a magnetic core formed of an amorphous magnetic material having a Curie temperature of 250° C. or higher and having a strip shape with a thickness of about 70 μm or less.

[Effect]

According to the configuration of the present invention, the magnetic core is made of an amorphous magnetic material having a thin strip shape with a thickness of 70 μm or less and a Curie temperature of 250° C. or higher, thereby making it possible to create a current transformer that is stable in terms of frequency and temperature. If used in devices, stable lighting operation will be possible, and the increased saturation magnetic flux density will allow the magnetic core to be made smaller.

〔Example〕

An embodiment of the present invention will be explained based on FIGS. 1 to 5. That is, amorphous magnetic material F eqqs
A toroidal magnetic core was prepared for is Baa, and then subjected to appropriate heat treatment and DC hysteresis characteristics were measured. The results are shown in FIG.

In this DC hysteresis characteristic, the saturation magnetic flux density is 14
000G, residual magnetic flux density 4800G, coercive force 0.060
It was e. Further, the magnetostriction constant λS of the magnetic material is 20X
lO-6, Curie temperature is 358°C.

Next, the frequency characteristics of this amorphous magnetic material were measured using an impedance analyzer (YHP4192A), and the results shown in FIG. 2 were obtained. From this graph, 1ookH
It was found that the magnetic permeability up to z is almost constant, and that it has higher performance than ferrite. Further, as can be seen from the above equation (5), since the l ratio with respect to frequency is constant, a current transformer having stable frequency characteristics and a good 3 degrees can be obtained.

In addition, as a result of measuring the temperature characteristics of magnetic permeability, it was found that the magnetic permeability was constant as shown in Figure 3, and -10'
The change in magnetic permeability between C and 100 C was 2 (1/' C), which was extremely thermally stable.

Furthermore, the frequency characteristics of magnetic permeability depend on the thickness of the amorphous magnetic ribbon. This is thought to be because the magnetic flux flowing through the ribbon causes eddy currents to flow inside the ribbon, thereby interfering with the magnetic flux. Therefore, in order to quantitatively understand the magnetic permeability, the thickness of the ribbon was varied and measured, and the results are shown in FIG. In the figure, Q1 is a graph of this example, and Q2 is a graph of ferrite.

As is clear from these results, it can be seen that this example has higher magnetic permeability than ferrite, that is, is superior to that of ferrite at a thickness of about 70 μm or less.

Furthermore, since the change in magnetic permeability with temperature depends on the Curie temperature of the material, we measured the relationship between the rate of change in magnetic permeability with temperature and the Curie temperature for various amorphous magnetic materials.

As a result, as shown in FIG. 5S, although the degree to which the Curie temperature decreases increases, it can be seen that this embodiment has sufficient superiority over ferrite at temperatures above 250°C.

Therefore, by forming the magnetic core from an amorphous magnetic material in the form of a ribbon with a thickness of 70 μm or less and a Curie temperature of 250° C. or higher, a current transformer that is stable in terms of frequency and temperature becomes possible, and the inverter lighting device shown in FIG. When applied to , stable lighting operation became possible. Furthermore, the increased saturation magnetic flux density has enabled miniaturization.

In addition, when similar magnetic permeability measurements were performed on a silicon ribbon (Si-Fe) with a silicon content of 6.5% in addition to the one band of the amorphous magnetic material, the same tendency as in the above example was obtained. It has become clear that if the conditions of thickness and Curie temperature are satisfied, it is suitable as a current transformer.

〔Effect of the invention〕

According to the current transformer of this invention, the magnetic core has a thickness of 7
By forming a strip of 0 μm or less and made of an amorphous magnetic material with a Curie temperature of 250°C or higher, a current transformer that is stable in frequency and temperature is possible, and when applied to an inverter lighting device, stable lighting operation is possible. Furthermore, the increased saturation magnetic flux density has the effect of making it possible to downsize the magnetic core.

[Brief explanation of the drawing]

Figure 1 is a DC hysteresis characteristic diagram of an amorphous magnetic material according to an embodiment of the present invention, Figure 2 is a frequency characteristic diagram of magnetic permeability, Figure 3 is a temperature characteristic diagram of magnetic permeability, and Figure 4 is a diagram of magnetic permeability characteristics. The characteristic diagram for the thickness of the band, the fifth circle is the characteristic diagram for the temperature change rate of i3 magnetic coefficient as a function of the Curie temperature, Figure 6 is the inverter lighting circuit diagram, Figure 7 is the principle diagram of the current transformer, and the eighth circle is the characteristic diagram for the Curie temperature.
The figure is a temperature characteristic diagram of magnetic permeability of ferrite. Figure 3-18 Number of tears (in Hz) □ Capacity (0C) Figure Thickness of the arm etc. (μm) Curie i-ya (0C) Figure Figure

Claims (1)

[Claims] A thin strip with a thickness of about 70 μm or less and a Curie temperature of 250
A current transformer with a magnetic core made of amorphous magnetic material with a temperature of ℃ or higher.