什么是电容器的阻抗ESR频率特性

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通过了解电容器的频率特性,可以判断电力线消除噪声和抑制电压波动的能力。可以说它是设计电路时不可或缺的参数。阻抗大小| Z |这里描述了频率特性中的ESR和ESR。

如果角频率是ω并且电容器的静电容量是C,则在理想条件下电容器(图1)的阻抗Z可以用公式(1)表示。

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从公式(1)可以看出阻抗大小| Z |如图2所示,其趋势与频率成反比。由于理想电容器没有损耗,因此等效串联电阻(ESR)为零。

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图2.理想电容的频率特性

然而,除了电容分量C之外,实际电容器(图3)由于电介质或电极损耗以及由电极或电线产生的寄生电感(ESL)而具有电阻(ESR)。因此,| Z |的频率特性如图4所示,V形是V形(一些电容器可以变成U形)曲线,并且ESR还表现出对应于损耗值的频率特性。

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图3.实际电容器

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图4. | Z |/ESR实际电容的频率特性(示例)

之所以| Z |和ESR成为图4的曲线如下。

低频范围:| Z |在低频范围内与理想电容器相同,并且两者都倾向于与频率成反比。 ESR值还显示对应于由介电极化延迟引起的介电损耗的特性。

Near the resonance point: When the frequency increases, |Z| will be affected by the ESR caused by the parasitic inductance or the specific resistance of the electrode, and will deviate from the ideal capacitor (red dotted line), showing the minimum value. The frequency at which |Z| is the minimum value is called the natural frequency, and |Z|=ESR. If it is greater than the natural frequency, the component characteristics are converted from capacitors to inductors, and |Z| is increased. A range below the natural frequency is called a capacitive field, and vice versa is called an inductive field.

In addition to the dielectric loss, ESR is also affected by the loss of the electrode itself against the stroke.

High frequency range: The characteristic of |Z| in the high frequency range above the resonance point is determined by the parasitic inductance (L). The |Z| of the high frequency range can be approximated by the formula (2) and increases in proportion to the frequency.

ESR gradually shows the effects of electrode skin effect and proximity effect.

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The above is the frequency characteristic of the actual capacitor. It is important that the higher the frequency, the less the effects of parasitic components ESR or ESL can be ignored. With the increasing use of capacitors in the high frequency field, ESR and ESL, like electrostatic capacitance values, are important parameters for capacitor performance.

The above has a great influence on the frequency characteristics of the capacitor parasitic components ESR and ESL. The parasitic composition will vary depending on the type of capacitor. Next, the difference in frequency characteristics of different types of capacitors will be described.

Fig. 5 shows the frequency characteristics of |Z| and ESR of various capacitors having an electrostatic capacity of 10 uF. Except for film capacitors, all are SMD type capacitors.

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Figure 5. |Z|/ESR frequency characteristics of various capacitors

xx图5中所示的电容器的电容值均为10uF,因此容量范围| Z |小于1kHz的频率是相同的值。但是,当频率高于1 kHz时,| Z |因为铝电解电容器或钽电解电容器的电解质材料的电阻率增加,所以铝电解电容器或钽电解电容器的电容器大于多层陶瓷电容器或薄膜电容器的电阻率,导致ESR增加。金属材料用于薄膜电容器或多层陶瓷电容器的电极中,因此ESR非常低。

多层陶瓷电容器和引线型薄膜电容器的特性在谐振点附近基本相同,但多层陶瓷电容器的自振频率高,| Z |。感应范围很小。这是因为仅引线型薄膜电容器的引脚线部分的电感增加。

从以上结果可以得出结论,SMD型多层陶瓷电容器在宽频率范围内具有低阻抗,并且也最适合于高频应用。

根据原材料和形状,多层陶瓷电容器可分为多种类型。下面解释这些因素对频率特性的影响。

电容域中的ESR由介电材料产生的介电损耗决定。由于使用强电介质,2类(类型2)中的高介电比材料趋于增加ESR。 Class1(Class 1)温度补偿材料使用一般电介质,因此介电损耗非常小,而且ESR值也很小。

除了电极材料的电阻率,电极形状(厚度,长度,宽度)和电极材料的特定电阻率之外,在与感应场的谐振点附近的高频场中的ESR受趋肤效应或邻近效应的影响。层数。 Ni通常用作电极材料,但在低损耗型电容器中,有时使用具有较低电阻率的Cu作为电极材料。

多层陶瓷电容器的ESL对内部电极结构非常敏感。当内电极的长度为l,宽度为w,厚度为d时,电极电感ESL可由F.W.Grover的公式(3)表示。

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从该公式可知,电容器的电极越短,ESL越宽越厚。

图6表示各尺寸多层陶瓷电容器的额定容量与固有频率之间的关系。容量相同,尺寸越小,自振频率越高,ESL越小。因此,可以说具有短长度l的小电容器适用于高频场。

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图6.额定容量值与每种尺寸固有频率之间的关系