磁环(铁芯)选用要点

磁環（鐵芯）選用要點

Ferrite分類

MnZn

NiZn

NiZnCu

用途：High Frequency Swithcing Mode Power Supplies

製造商：TDK、EPCOS

型式：EFD15

材質：MnZn錳鋅

居里點，至少要高於200℃

μi：2200± 25 % @T = 25 °C

BS：390mT @T=100℃

飽和磁通密度Bs：

最大磁通密度Bm：

Ae：15mm2

AL：780 + 30/– 20 %

Frequency range：25K~500KHz（要有最低和最高）

ROHS

Curie Temperature：>210℃

Pv(Core lss)：390kW/m3 @300kHz,100mT,100℃

(Pcv)

Bs儘量高，Br儘量低，才能達到小體積大功率

選用高磁導率的CORE，使激磁電感盡量大，讓磁化電流盡可能低

UP TO 500KHz（500K以下）

名詞解釋：

鐵損是由於在鐵芯中的變更磁場所造成,這個損失與操作頻率及總流動的磁通量有關,總鐵損由三個成份組成,磁滯損,渦流損及殘留損.這些損失

因磁性材料不同而異,在如高功率及高頻率切換調整器和RF的設計需要小心選擇鐵芯種類以降低鐵損使電感的表現最佳.

■ CURIE TEMPERATURE 居禮溫度

The temperature above which a ferrite core loses its magnetic properties. The core's permeability typically increases dramatically as the

core temperature approaches the curie temperature which causes the

inductance to increase. The permeability drops to near unity at the curie temperature which causes the inductance to drop dramatically. The curie point is the temperature at which the initial permeability has dropped to 10% of its original value at room temperature.

在此一溫度以上鐵氧磁體鐵芯失去磁性質,鐵芯的磁導率一般在接近居禮溫度時會急速上升因而電感值亦上升,於居禮溫度時,導磁率約降至一,

因而使電感值急速下降,當初導磁率下降為在室溫下之初導磁率的10％時,其溫

度稱之為居禮溫度.

■ DCR ( DC RESISTANCE ) 直流電阻

The resistance of the inductor winding measured with no alternating current. The DCR is most often minimized in the design of an

inductor. The unit of measure is ohms, and it is usually specified as a maximum rating.

電感線圈在非交流電下量得之電阻.在電感設計中,直流電阻愈小愈好,其量測單位為歐姆,通常以其最大值為標註.

■ DISTRIBUTED CAPACITANCE 分佈電容值

In the construction of an inductor, each turn of wire or conductor acts as a capacitor plate. The combined effects of each turn can be represented as a single capacitance known as the distributed capacitance. This capacitance is in parallel with the inductor. This parallel combination will resonate at some frequency which is called the

self-resonant frequency (SRF). Lower distributed capacitances for a given inductance value will result in a higher SRF value and vice versa. (Also see SRF.)

在電感的結構中,每一圈的繞線或導體有如電容電板一般的作用.其每圈結合起

來的效果,有如單一之電容值,稱之分佈電容值.與電感並聯的.如

此並聯的結合使得電感在某頻率下會產生諧振,稱之自我共振頻率(SRF),在一定電感值下,較低的分佈電容值會有較高之自我共振,反之亦然.

■ EDDY CURRENT LOSSES 渦流損

Eddy current losses are present in both the magnetic core and winding of an inductor. Eddy currents in the winding (or conductor)

contribute to two main types of losses: losses due to proximity effects and skin effects. As for the core losses, an electric field around the flux lines in the magnetic field is generated by alternating magnetic flux. This will result in eddy currents if the magnetic core material has