1、铝电解电容的寿命电源产品中经常用到铝电解电容，他的寿命往往决定了整个产品的寿命。因此，了解如何计算铝电解电容的寿命很有必要。下面将我的一些心得整理出来，供大家参考。希望有助于提高国人的知识水平。说白了很简单，只不过很多人找不到相关的资料而已。同时也希望学校的教材中能够近早讲解相关知识。我尽量少翻译，因为我的语言能力及相关的专业术语还不行。仅供参考。Chapter 1 铝电解电容的特性1.1 Circuit model （等效模型）The following circuit models the aluminium electrolytic capacitors normal operation
2、 as well as the over voltage and reverse voltage behavior. （此模型包含正常运行，过压，反压时的特性）CA Cc RPESRL D= Anode capacitance (阳极电容)= Cathode capacitance(阴极电容)= Parallel resistance, due to dielectric (并联电阻)= Series resistance, as a result of connections, paper, electrolyte, ect. 等效串联电阻= Winding inductance and c
3、onnections 等效串联电感= Over and reverse voltage 等效稳压管The capacitance Ca and Cc are the capacitance of the capacitor and is frequency and temperature depended. （Ca and Cc，它的容量是频率及温度的函数）The resistance ESR is the equivalent series resistance which is frequency and temperature depended. It also increases wi
4、th the rated voltage. （ESR 是频率及温度的函数，随着额定电压的增加而增加）The inductance L is the equivalent series inductance, and its independent for both frequency and temperature. It increases with terminal spacing. （L 是频率及温度的函数）The resistance Rp is the equivalent parallel resistance and accounts for leakage current in
5、 the capacitor. It decreases with increasing the capacitance, temperature and voltage and it increases with time. （Rp 的大小决定了漏电流的大小，随着容量温度电压的增加而降低，随着使用时间的延长而增加）The zener diode D models the over voltage and reverse voltage behavior. Application of over voltage on the order of 50 V beyond the capacitor
6、s surge voltage rating causes high。 （D 模拟过压及加反向电压时特性）Leakage current and a constant voltage-operating mode quite like the reverse conduction of a zener diode. Applications of reverse voltage much beyond 1.5 V causes high leakage current quite like the forward conduction of a diode. Neither of these
7、operating modes can be maintained for long because hydrogen gas is produced, and the pressure built up will cause failure. （加到电容两端的反向电压不能大于 1.5V）1.2 Capacitance （电容的容量）The rated capacitance is the nominal capacitance and it is specified at 120 Hz and a temperature of 25C. Capacitance is a measure of
8、 the energy storage capability of a capacitor at a given voltage. （额定容量： 标称电压，120Hz, 25C 时测量） 。The capacitance decreases under load conditions and increases under no load conditions over time. When reverse voltage or excessive ripple current is applied, or when the capacitor is repeatedly charged an
9、d discharged, an aluminium oxide film is formed on the cathode foil. This film induces a sharp capacitance drop. Capacitance in aluminium electrolytic capacitors is also affected by frequency changes. For example, the capacitance falls as the frequency rises. Variation of magnitude depends on capaci
10、tor type. （电容上的纹波电流，频繁地充放电导致阴极箔氧化，容量急剧下降）1.3 Equivalent series resistance (ESR)等效串联电阻The equivalent Series Resistance (ESR) is the sum of all the internal resistances of a capacitor measured in Ohms. It includes:- Resistance due to aluminium oxide thickness 源于氧化铝厚度的电阻- Resistance due to electrolyte
11、/ spacer combination源于电解液/垫片结电阻- Resistance due to materials (Foil length; Tabbing; Lead wires; Contact resistance)源于材料的电阻（箔片长度，Tabbing，导线，接触电阻）At low frequencies (10 100 Hz) the ESR is determined by the oxide thickness,electrolyte / spacer combination and the materials. Above the 100 Hz electrolyte
12、 / spacer combination and the materials predominate.低频时（10-100HZ） ，ESR 由氧化铝厚度，电解液/垫片结电阻，材料决定。100HZ 以上，电解液/ 垫片结电阻，材料主宰 ESRThe lower the ESR the higher the current carrying ability the capacitor will have. The amount of heat generated by ripple current depends upon the ESR of the capacitor.ESR 越小，电流承受
13、能力越高，浪涌电流产生的热量取决于电容的 ESRESR is both frequency and temperature dependent, increasing either will cause a reduction in ESR. The ESR is an important parameter in calculating life expectancy as the power dissipation (internally generated heat) is directly proportional to its value.The limit is generally
14、 established at 120 Hz and 20 C.ESR 具有频率和温度属性，增加频率或者属性会降低 ESR，ESR 是计算期望寿命时的重要参数之一，因为功耗（内部发热）与它的值直接成正比限度通常确定为 120HZ 和 20 摄氏度（centigrade）The ESR of the electrolytic capacitor can cause another effect, especially above the 10 kHz where the ESR is the dominant contribution to the capacitors impedance.铝电
15、解电容的 ESR 会导致另外一个效应，特别当频率高于 10Khz ESR 在电容的阻抗中占主导地位的时候When a current charges / discharges the capacitor, the voltage across the capacitor will increase / decrease:dtVCIand causes a voltage drop over the ESR （流过电容的充放电电流因为 ESR 而产生纹波电压）ESR如果电容由低占空比，高频脉冲电流充电时， 比较典型的是 fly-back 电源的输出滤波电容，ESR 引起的纹波电压是最重要的，导致
16、必须选用合适 ESR 的电容来满足要求。电容的容量不是主要考虑的问题。电容 ESR 的危害：（ 1）电容上的纹波电压（2）纹波电流流过 ESR 发热，使电容寿命缩短。（DF:dissipation factor 损耗因子） ESR 与 DF 的关系 (Fig. 1.2) 1.4 Dissipation factor (tan) 损耗角或损耗因子影响损耗角或损耗因子的因素：电容的 ESR，容量，工作频率The dissipation factor (also called Angle of loss or tangent delta) is a measure of the losses (or
17、, the power factor) of a capacitor. When sinusoidal current is applied to an ideal capacitor, the phase of current should gain /2, however the phase of current actually delays from /2 on a realistic capacitor. The loss in angular velocity is called loss angle and represented by ”.The tan is decided
18、by ESR (Equivalent Series Resistance), the capacitance (C) and the Frequency (F) usually at 120Hz and 20oCESR 与 DF 的关系 ESRtan损耗因子 %10DF1.5 The impedance 阻抗阻抗 CLjXESRZCX1LX阻抗的模 221CL通常优先选择中频段阻抗较低的电容。好电容具有较低的阻抗和 ESR.1.6 Ripple current (纹波电流) - 很重要The ripple current Ir is the r.m.s. alternate current v
19、alue that can be directly applied to the capacitor. The maximum permissible ripple current is dependent on the case style and surface area and ESR, and maximum allowed core temperature.纹波电流 Ir ： 电容上流过的交流电流的有效值允许的最大纹波电流受限于：外壳的形状，电容的表面积，ESR，最大允许的核心温度 If the ripple current applied is higher than the sp
20、ecified maximum permissible ripple current, the life of the capacitor becomes shorter.如果实际的纹波电流大于最大允许纹波电流，电容的寿命极大缩短In general, increasing ripple current is possible by changing the following parameters:- Lower ambient temperatures （降低环境温度）- Lower ESR (note: the higher the Frequency, the lower the ES
21、R) （降低 ESR，频率越高 ESR 越低）- Improve heat transfer through heat sinking and / or forced air cooling （良好的散热）- Increase case size （加大电容的尺寸）- Voltage derating （额定电压降额使用, 例如 450V 的电容用于 300V 的应用下）For more detailed information about calculating the ripple current see chapter 7 paragraph 7.41.7 Voltage 电压- The
22、 rated voltage 额定电压峰值电压（交流与直流的和）必须小于额定电压The rated voltage can be applied to a capacitor within temperature and reference margins. The sum of continuous and alternate voltage applied to the capacitor cannot exceed rated voltage. The maximum permissible ripple current limits the alternate voltage.Dera
23、ting the applied voltage will reduce the failure rate of the capacitor. Higher rated voltage capacitors may be substituted for lower rated voltage capacitors as long as can size, DF and ESR ratings are also compatible.- The reverse voltage 反向电压不能加反向电压，能够承受 1.5V 1 min 的反向电压反向电压的危害：发热，阴极氧化，产生大量氢气，使电容爆
24、裂- The surge voltage 浪涌电压电容短时间能够承受的最大过压（5 min 的周期内不超过 30 秒的脉冲过压）危害与反向电压的危害一样。IEC 的标准（最大允许的浪涌电压）：VP = 1.15 x Vrated for Vrated 315 VDC Rated voltage (V) 4 6.3 10 16 25 35 50 63 80 100 160 180 200 250 315 350 400 450Surge voltage (V) 5 8 13 20 32 44 63 79 100 125 200 225 250 300 365 400 450 500最大允许的浪涌
25、电压与最大额定电压的关系浪涌电流指电源接通瞬间，流入电源设备的峰值电流。由于输入滤波电容迅速充电，所以该峰值电流远远大于稳态输入电流。电源应该限制 AC 开关、整流桥、保险丝、EMI 滤波器件能承受的浪涌水平。反复开关环路，AC 输入电压不应损坏电源或者导致保险丝烧断。电路在遭雷击和在接通、断开电感负载或大型负载时常常会产生很高的操作过电压，这种瞬时过电压（或过电流）称为浪涌电压（或浪涌电流），是一种瞬变干扰。浪涌电压应用于电源上电的瞬间，电容上往往有过充电压，特别是 PFC 电路。- The transient voltage 瞬态电压Aluminium electrolytic capac
26、itors can generally withstand extreme over voltage transients of limited energy. Applications of over voltage more than about 50 V beyond the capacitors surge voltage rating causes high leakage current and a constant voltage operating mode like the reverse conduction of a zener diode. The capacitor
27、may fail short if the electrolyte cannot take the voltage stress, but even if it can, this operating mode cannot be maintained for long because hydrogen gas is produced by the capacitor, and the pressure built up will cause failure. 1.8 Temperature 温度（纹波电流与 ESR 的交互作用的后果）热阻可分成两部分：内部热阻（从核心到外壳）和 外部热阻（从
28、外壳到周围的环境）内部热阻的大小取决于制造工艺。良好的散热可以降低外部热阻。外壳的面积也很重要。1.8.1 Heat rise of case surface （外壳表面的温升，从外壳到周围的环境）AESRITcr2Where:TcAESRIr= Heat rise at the surface of the capacitor 电容表面的温升= Heat Radiation Constant (W/C cm) 热辐射常数= Surface Area of Can 外壳的表面积= Equivalent Series Resistance 等效串联电阻= Ripple current 纹波电流有
29、效值经验公式 W/C cm 2.031.2A外壳的表面积越大，越小。； ESRITcr28.0435 8.0435A， 圆柱形电解电容的表面积，D 是直径，h 是高度hA*2=从外壳到周围的环境的热阻同样的外壳的表面积，具有同样的1.8.2 内部热阻（从核心到外壳）经验定律： TcjTj= Heat rise at the core of the capacitor element 从核心到外壳的温升= Thermal resistance 内部热阻（从核心到外壳）内部热阻与外壳的尺寸密切相关，经验结论：外壳的直径 3 8 10 12.5 16 18 2022 25 30 35内部热阻 1 1
30、.1 1.2 1.3 1.4 1.5 1.6Chapter 2 计算铝电解电容的寿命 L2.1 Introduction每个厂商都有自己的计算方法，但都遵循一定的原则：温度极大的影响铝电解电容内的电解液的扩散速度。根据 Arrhenius 的物理定律，温度每升高 10 度，电解液的扩散速度加倍；换句话说，铝电解电容的寿命缩短一倍。A physic law (According the Arrhenius law) teaches us that increasing the temperature 10 C will double the diffusion of electrolyte. 为
31、了便于计算和理解，将其分成三部分：（1） 基本寿命 Lo：由外壳体积，热辐射性能，制造工艺等决定。最大环境温度及最大纹波电流下的寿命就是基本寿命。厂商都会提供或在产品说明书中注明。（2） 环境温度函数 f(T)：电解液的扩散（3） 纹波电流函数 f(I)：ESR 引起的热损耗后两者导致铝电解电容核心温度上升，电解液的扩散速度加快。 )().(.IfTfLo根据 Arrhenius 定律：L 与 成反比，Tj: 电解电容的核心温度102j热阻定律： ；TjcaTj； ESRIr2TcTjTa: 电解电容周围的温度，即环境温度； Tc: 电解电容外壳的温度因为 Ta 不易测出，但 Tc 很好测量；
32、可以根据 Tc 算出 Ta； ccj环境温度函数 f(T)： 210To)Tf(2.2 以下均为个人观点，不能 100%正确。在厂商提供的数据中一般包含：后缀为 0，则认为是厂商提供的极限值最高（环境）温度 Ta0 ： 一般选用 105 度的电解电容 最大环境温度下最大允许的纹波电流 Ip0, 它的校正系数为 1；120Hz 或 100kHz， 不同的厂家有不同的表示方法校正系数 Correction coefficient：不同频率纹波电流之间的关系在 Ta0 和 Ip0 条件下所产生的温升： Tj0； 本人认为是核心与外壳之间的温差，也可能是核心与 Ta0 之间的温差下表是 Rubycon
33、 BXA 系列电容不同频率纹波电流之间的关系 series frequency correction factor tableFrequency Hz 120 1k 10k 100k =Correction coefficient 0.50 定义为 CLF 0.8 0.9 1.00 定义为 CHF注意：有的厂家定义 120Hz 时校正系数为 1，有的厂家定义 100kHz 时校正系数为 1。大多数情况下电容上会流过多种频率的纹波电流，需要计算平均电流，利用傅立叶分析，将纹波电流划分为低频和高频两部分。同时注意，不同频率时 ESR 不同。从功耗角度来考虑不同频率纹波电流之间的相互转换。功耗引起的
34、发热是影响电容寿命的根本原因。若只有一种频率的纹波电流流过电容，而不同频率时 ESR 不同，所以ESRIESRI HFLF22； CLHLFHLF CIIHFLFLF一般认为纹波电流主要包含两部分：低频 120Hz 和高频 100kHz (个人观点)纹波电流有效值 Ir ： 210)()(10)()(2 TjcaTjocaoTjcaTjocao LL 环境温度函数 f(T)： ； )(f纹波电流函数 f(I)： 10)()10)()( 22TjoTjcjoTcITjoIprjIporTj 22)()(c计算求得的实际环境温度 Ta: TjoIprcTa2)(若有兴趣，可以用 excel 做成一
35、个合适的文件，一劳永逸。2.3 部分厂商提供的纹波电流函数 f(I)可气的是都是日本鬼子的，没办法。但是可以通过学习它们的东西来提高我们。2.3.1 Nichicon Ripple current coefficient (given by themanufacturer on request)T Maximum rated temperatureTo Ambient temperature when operatedI Applied current at the temperature of To2)( 302*1If oTPIIIp Allowable ripple current at
36、 maximum rated temperature 120 Hz2.3.2 NCC (Nippon Chemi-con)To Core temp rise when operated at max allowable ripple currentT Actual Core temp rise when operated at actual ripple current (catalogue)I Applied ripple current at temperature of To2)(5*2If TIpoTIp Allowable max ripple current at maximum
37、rated temperature 100 kHz2.3.3 PanasonicT Temperature rise at constant current (C) (read from graphic)I Applied ripple current at temperature of To2)(102If PITIp Allowable ripple current at maximum rated temperature 100 kHz 2.3.4 RubyconTjo Internal temp. rise when max. permissible ripple current is
38、 appliedTj Heat rise by ripple current at the core of the capacitor elementI Applied ripple current at temperature IP Allowable ripple current at maximum rated temperature 2)(2*25.01If AIpjoTjoTjoA Temperature factors when acceleration coefficient becomes twice greaterAforuseTjFor0 IpTjo*25.012fj2 A2joIp*T
