Research on a New Type of High Frequency and High Current Inductor

1 Introduction

Inductors are widely used in electronic devices as energy storage and filtering components. With the development of science and technology, inductors are becoming increasingly miniaturized, and the volume and weight requirements are becoming increasingly stringent. In particular, a large number of high-frequency, high-current filter inductors are used in aerospace electronic equipment. Due to their large current, high ampere-turns, and small size, the traditional air gap method cannot meet the design requirements. This article will introduce a new type of high-frequency, high-current, small-volume inductor.

2. Fabrication of Inductors

Generally, inductors use the method of opening an air gap to increase the constant magnetic range. The larger the constant magnetic range, the longer the air gap and the lower the corresponding magnetic permeability. To achieve a certain inductance, the cross-sectional area and volume of the core must be increased. The following is a DC characteristic test of an air-gap inductor. The core is amorphous, the size is 25/45×20, the air gap is 2mm, and the coil has 34 turns. The test data is as follows:

Table 1 DC characteristics of air-gap inductors

At 30A, its inductance is only 25.3% of that at 0A. In order to improve the anti-saturation performance of the inductor, we add a constant magnetic material to the air gap of the inductor core. The area of ​​the constant magnetic sheet is exactly equal to the cross-sectional area of ​​the inductor core, and the thickness is 2mm. Then the core is encapsulated as a whole, and a coil is wound on the outside to make an inductor. The inductors made by this research institute are all 25/45×20, with an air gap of 2mm, and the above-mentioned constant magnetic sheet is inserted and wound with 34 turns of coil. The coercive force (Hcb) of the constant magnetic material is as high as 8500Oe, the maximum magnetic energy product is 191kJ/m3, and the operating temperature is 250℃.

3. Inductance performance test

3.1 Magnetization curve

Usually the magnetization curve of the inductor is symmetrical, and the positive and negative magnetic energy products are equal. However, after adding the permanent magnetic material, the positive and negative magnetic energy products are not equal, as shown in Figure 1:

From the figure, we can see that due to the effect of the constant magnetic sheet, the hysteresis loop is offset. When the applied DC magnetic field is in the same direction as the constant magnetic field, H net magnetic field = H DC + H constant magnetic field, so the magnetic core quickly enters saturation, the magnetic permeability decreases, and the inductance decreases; when the applied DC magnetic field is opposite to the constant magnetic field, H net magnetic field = H DC - H constant magnetic field, the magnetic core is not easy to saturate, the magnetic permeability increases linearly, and the inductance remains basically unchanged. In this way, when the inductor is used as a DC filter element, as long as the DC magnetic field of the inductor is opposite to the constant magnetic field, the ampere-turns of the inductor can be greatly increased, the anti-saturation ability can be improved, and the inductor can be miniaturized.

3.2 DC bias test

After the inductor tested in Table 1 is inserted into the permanent magnetic sheet, it is processed into a finished inductor. Three finished products are taken as test samples. The DC characteristics are tested as shown in Table 2 (the test instrument is HP4284A, and the test frequency is 1kHz):

Table 2 DC characteristics of constant magnetic inductance

From the table above, we can see that after 10 amperes, the inductance of the inductor is extremely constant, with a drop of only 4% at most. Compared with the case without the constant magnetic sheet, the anti-saturation performance is significantly improved. (Due to equipment reasons, only 35A, 1190AT was tested, at which time the magnetic field strength was 142Oe).

3.3 Temperature test and mechanical impact vibration test

The above inductor was cycled three times at -55℃, 2h130℃, 2hrs, and then its inductance change under DC bias was tested, as shown in Table 3.

Comparing the data in Table 2 and Table 3, we can see that after the hot and cold cycle test, the inductance and anti-saturation ability of the inductor have not changed.

The above test samples were then tested according to the routine test requirements for military electronic products. The test conditions are as follows: Table 3 DC characteristics of constant magnetic inductance after hot and cold shock

(1) Random vibration

15～250Hz0.04g2/Hz (g2/Hz: power spectrum density)

250～300Hz－4dB/oct（oct: octave）

300～1000Hz0.025g2/Hz

1000～2000Hz－6dB/oct

Forward 1h

(2) Collision test (GB/T15290-94)

50m/s2, 11ms, forward 1000 times

After the random vibration and collision tests, the inductor was tested for changes in inductance under DC bias. The test results showed that the inductor passed routine tests and met the requirements for military electronic products.

4 Conclusion

As an inductor used for DC filtering, inserting constant magnetic material into the magnetic core can greatly improve its performance and increase the working magnetic field strength. High and low temperature cycle tests and impact vibration tests have proved that the inductor core made using this technology meets the requirements for use in aerospace equipment. Currently, the product has been provided in small batches to a unit in Shanghai and has been successfully used in aerospace equipment.