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如何提高电解电容的在电子产品中的使用寿命和稳定性?
时间:2022-02-22 14:19:29   浏览次数:
  如何提高电解电容在电子产品中的使用寿命和可靠性?今天小编就和大家详细的介绍一下,电解电容的使用寿命和稳定性与哪些环境因素有关。
  How to improve the service life and reliability of electrolytic capacitors in electronic products? Today, I will introduce in detail to you what environmental factors are related to the service life and stability of electrolytic capacitors.
  1.适当降低工作电压
  Properly reduce the working voltage
  降低电解电容器的工作电压是延长电容器使用寿命,提高可靠性的最有效方法。因为电解电容器的失效率与外加电压和电容器额定电压之比的二次方成正比电解电容器用于电源滤波电路的场合最多,输入电压发生变化或负载突然开路,滤波电容器两端的电压都会随之发生变化,如果不进行降额设计,很可能使电容器击穿此外,从输入端进来的交流电压并非是正弦波电压,一般非正弦波的峰值电压要比正弦波电压高,可对电容器的寿命和可靠性造成较大影响。
  Reducing the working voltage of electrolytic capacitor is the most effective way to prolong the service life and improve the reliability of capacitor. Because the failure rate of electrolytic capacitor is directly proportional to the quadratic of the ratio of applied voltage and rated voltage of capacitor, electrolytic capacitor is most used in power filter circuit. When the input voltage changes or the load is suddenly open, the voltage at both ends of filter capacitor will change accordingly. If the derating design is not carried out, the capacitor is likely to break down. In addition, The AC voltage coming in from the input is not a sine wave voltage. Generally, the peak voltage of non sine wave is higher than that of sine wave, which can have a great impact on the service life and reliability of capacitor.
  所以,在设计时,使用时要对电解电容器的工作电压进行较大幅度的降额对电解电容器电压的降额幅度要根据整机的可靠性要求及电容器使用的具体电路而定一般可分三级,一级为额定电压的50%;二级为60%;三级为70%高压大容量的电容器应选择较大的降额幅度电容器的容量越大,氧化膜的面积越大,出现介质缺陷的机率也越大,可靠性越低。
  Therefore, during design, the working voltage of electrolytic capacitor shall be greatly reduced during use. The voltage reduction range of electrolytic capacitor shall be determined according to the reliability requirements of the whole machine and the specific circuit used by the capacitor. Generally, it can be divided into three levels, and the first level is 50% of the rated voltage; 60% for level II; The capacitor with 70% high voltage and large capacity in the third stage shall be selected with a large derating range. The larger the capacity of the capacitor, the larger the area of the oxide film, the greater the probability of dielectric defects and the lower the reliability.
  2.充分考虑纹波电压
  Full consideration of ripple voltage
  一般电解电容器都有正负极之分,当用于既有直流电压又有交流电压分量的脉动电路中时,其工作特性应特别注意电解电容在使用时,一定要符合电解电容器两端规定的电压极性要求当用于级间耦合或脉冲电路时,在电容器上施加的直流电压还要叠加交流电压成分的幅值,在某些情况下有可能使交流分量的负峰值电压超过正直流电压值,从而使极性电容器处在反向工作状态,这样会使电容器的漏电流剧增,进而破坏正向工作特性而造成失效。
  Generally, electrolytic capacitors are divided into positive and negative poles. When used in pulsating circuits with both DC voltage and AC voltage components, special attention shall be paid to their working characteristics. When used, electrolytic capacitors must meet the voltage polarity requirements specified at both ends of electrolytic capacitors. When used in interstage coupling or pulse circuits, The DC voltage applied on the capacitor should also be superimposed with the amplitude of the AC voltage component. In some cases, it is possible to make the negative peak voltage of the AC component exceed the positive DC voltage value, so that the polar capacitor is in the reverse working state. In this way, the leakage current of the capacitor will increase sharply, which will destroy the positive working characteristics and cause failure.
  因此,当电容器两端存在脉动交流成分时,交流峰值电压与所加直流电压之和不应超过电容器的额定工作电压其原因是交流成分引起电容器的温升发热比直流成分严重的多,所以要严格控制纹波的大小,一般不应超过电容器额定工作电压的百分之二十即可对于钽电解电容器,也应控制在百分之十以内由于纹波电压可使电解液极化,且对损耗电阻RS影响很大,所以要对加到电容器上的纹波峰值电压进行有效的控制。
  Therefore, when there is pulsating AC component at both ends of the capacitor, the sum of AC peak voltage and applied DC voltage should not exceed the rated working voltage of the capacitor. The reason is that the temperature rise and heating of the capacitor caused by AC component is much more serious than that of DC component, so the ripple should be strictly controlled, Generally, it should not exceed 20% of the rated working voltage of the capacitor. For tantalum electrolytic capacitor, it should also be controlled within 10%. Because the ripple voltage can polarize the electrolyte and has a great impact on the loss resistance Rs, it is necessary to effectively control the ripple peak voltage added to the capacitor.
  要保证电容器可靠的工作,加到电容器上的纹波电压应小于上式计算出来的纹波峰值电压。由于一般有极性电容器不能承受反向电压,所以有极性电容器在有极性变换或纯交流电路中是不容许的,而应选用无极性钽解电容器(如CA74全密封固体钽电容器)。无极钽电容器实际上是用两只有极性的钽电容器背靠背串联起来的,即使电容器在交流电路中始终有一支钽电容处在正极性状态。
  To ensure the reliable operation of the capacitor, the ripple voltage added to the capacitor shall be less than the ripple peak voltage calculated by the above formula. Generally, polar capacitors cannot withstand reverse voltage, so polar capacitors are not allowed in polar conversion or pure AC circuits, and non-polar tantalum capacitors (such as ca74 fully sealed solid tantalum capacitors) should be selected. In fact, two tantalum capacitors with polarity are connected back-to-back in series, even if one tantalum capacitor is always in the positive state in the AC circuit.
  3.电解电容器的工作频率
  Operating frequency of electrolytic capacitor
  电解电容器最适宜在工频条件下做电源的滤波或在低频电路中做旁路或级间耦合,而且电路阻抗愈低愈可靠电解电容器工作时,相当于一个电解槽,其中一个电极是电解液由于电解液的电阻比一般金属电极高得多,因此,电解电容器的串联等效电阻较大在直流或低频率条件下,等效串联电阻RS和等效电感L与实际电容器的介质绝缘电阻尺RP相比可以忽略不计而随着频率的升高,等效串联电阻RS和等效电感L都会随着增大等效串联电阻RS增大是由于"集肤效应"引起的,等效电感L是与频率成正比的磁场引起的。
  The electrolytic capacitor is most suitable for power filtering under power frequency conditions or bypass or interstage coupling in low-frequency circuits. The lower the circuit impedance, the more reliable. When the electrolytic capacitor works, it is equivalent to an electrolytic cell, one of which is electrolyte. Because the resistance of electrolyte is much higher than that of general metal electrodes, therefore, The series equivalent resistance of electrolytic capacitor is large. Under the condition of DC or low frequency, the equivalent series resistance Rs and equivalent inductance L are negligible compared with the dielectric insulation resistance ruler RP of actual capacitor. With the increase of frequency, the equivalent series resistance Rs and equivalent inductance L will increase. The increase of equivalent series resistance Rs is caused by "skin effect", The equivalent inductance L is caused by a magnetic field proportional to the frequency.
  一般情况下,频率增加时,容抗XC的值减小,而感抗XL则增加,这表明(XC-XL)2将随频率的增加而减小,当频率增加到某个频率点(XC-XL)2=0时,阻抗Z=RS此时电容器将出现谐振这是电容器对电路呈现纯电阻时的谐振点当频率高于电容器谐振点时,电容器实际上已变成一个电感而起不到电容器的作用了,所以要求一般电解电容器的使用频率不应超过20 kHz由于大多数材料的介电常数在频率的影响下,其容量随频率的提高会大幅度下降故当使用频率超过20 kHz时,其所允许的交流分量已很小,电容器的容量损失非常严重,此时一般可选择一只高频瓷介或云母电容器与之并联来作为高频通路,电解电容器由于容量大,可作为低频通路,其容量应大于高频电容器容量的100倍以上。
  Generally, when the frequency increases, the value of capacitive reactance XC decreases, while the inductive reactance XL increases, which indicates that (xc-xl) 2 will decrease with the increase of frequency. When the frequency increases to a certain frequency point (xc-xl) 2 = 0, the impedance z = rs. at this time, the capacitor will resonate. This is the resonance point when the capacitor presents pure resistance to the circuit. When the frequency is higher than the resonance point of the capacitor, In fact, the capacitor has become an inductor and can not play the role of capacitor, so it is required that the use frequency of general electrolytic capacitor should not exceed 20 kHz. Since the dielectric constant of most materials will decrease significantly with the increase of frequency under the influence of frequency, when the use frequency exceeds 20 kHz, the allowable AC component is very small, The capacity loss of the capacitor is very serious. At this time, generally, a high-frequency ceramic dielectric or mica capacitor can be selected in parallel as the high-frequency path. Due to its large capacity, the electrolytic capacitor can be used as the low-frequency path, and its capacity should be more than 100 times of the capacity of the high-frequency capacitor.
  由于电容器的大多数特性都在某种程度上受到频率的影响,所以要求使用频率应在谐振频率的1/2以上,使用频率过高不仅会损耗电路中的大量能量,而且可造成电容器内芯发热,从而影响电容器的可靠性。一般电解电容器应工作在10 kHz以下,如果使用频率超过10 kHz,有效容量将迅速下降,直到电容阻抗变成纯电阻一般在100 Hz~100kHz范围内,其容量随频率的变化,固体钽电容器的频率特性优于液体钽电容器,而液体钽电容器则在1 kHz~3 kHz范围内,其容量随频率变化的下降幅度为6%,当频率增加10 kHz以上时,下降幅度将高达65%左右这主要是由介质材料性质所决定的如果电解电容器不能满足使用要求,可以采用四线电解电容器或其它介质的电容器。
  Since most of the characteristics of the capacitor are affected by the frequency to some extent, it is required that the use frequency should be more than 1 / 2 of the resonant frequency. If the use frequency is too high, it will not only lose a lot of energy in the circuit, but also cause the inner core of the capacitor to heat up, which will affect the reliability of the capacitor. Generally, electrolytic capacitors should work below 10 kHz. If the frequency exceeds 10 kHz, the effective capacity will drop rapidly until the capacitance impedance becomes pure resistance, which is generally in the range of 100 Hz ~ 100 kHz. The capacity changes with frequency. The frequency characteristics of solid tantalum capacitors are better than liquid tantalum capacitors, while liquid tantalum capacitors are in the range of 1 kHz ~ 3 kHz, Its capacity decreases by 6% with the change of frequency. When the frequency increases by more than 10 kHz, the decrease will be as high as about 65%, which is mainly determined by the properties of dielectric materials. If the electrolytic capacitor cannot meet the use requirements, four wire electrolytic capacitor or capacitor of other media can be used.
  4.适当降低使用环境温度
  Reduce the ambient temperature properly
  在相同电压情况下,电解电容器的漏电流及损耗随温度的升高而变大,当温度从室温25℃上升到85℃时,漏电流通常将增大3倍电容器的漏电流及损耗是造成电容器发热的主要原因,所以降低电容器的使用环境温度,是延长电容器使用寿命,提高可靠性的有利措施,一般可按此温度降额要求进行设计铝电解电容器应降低额定温度20~40℃;固体钽电容器可降低额定温度15~25℃;液体钽电容器应降低额定温度15~30℃;铝电解电容器由于在负温下的损耗会急剧上升,所以一般额定温度为-20℃。
  Under the same voltage, the leakage current and loss of electrolytic capacitor increase with the increase of temperature. When the temperature rises from room temperature 25 ℃ to 85 ℃, the leakage current will usually increase by three times. The leakage current and loss of capacitor are the main reasons for the heating of capacitor. Therefore, reducing the service ambient temperature of capacitor is a favorable measure to prolong the service life and improve the reliability of capacitor, Generally, it can be designed according to this temperature derating requirement, and the rated temperature of aluminum electrolytic capacitor shall be reduced by 20 ~ 40 ℃; The rated temperature of solid tantalum capacitor can be reduced by 15 ~ 25 ℃; The rated temperature of liquid tantalum capacitor shall be reduced by 15 ~ 30 ℃; Since the loss of aluminum electrolytic capacitor will rise sharply under negative temperature, the general rated temperature is - 20 ℃.
  5.防止瞬间的大电流冲击和电路阻抗
  Prevent instantaneous high current impact and circuit impedance
  在使用中,随着环境温度的增加,电容器漏流也在增大,当有大浪涌电流通过时,漏电流可能发生"雪崩"现象而使电容器损坏。为了防止这种现象发生,应增加电路的阻抗,使回路的阻抗不小于3 Ω/V,否则可靠性就会相应降低。
  In use, with the increase of ambient temperature, the leakage current of the capacitor is also increasing. When a large surge current passes through, the leakage current may cause "avalanche" phenomenon and damage the capacitor. In order to prevent this phenomenon, the impedance of the circuit should be increased so that the impedance of the circuit is not less than 3 Ω / V, otherwise the reliability will be reduced accordingly.
  6.电容器安装和焊接的可靠性
  Reliability of capacitor installation and welding
  如果电容器是近期出厂的产品,而且可焊性已达到要求,一般不需要浸锡预处理。而如果储存时间较长则在使用前需进行浸锡处理,浸锡处理应控制在技术规范规定的封口3.2 mm以外,并避免时间过长或温度过高,造成封口熔化或引线与电极脱焊对于片式电容器,还应避免使用活性高、酸性强的助焊剂,以免清洗不干净、渗透、腐蚀和扩散而影响产品可靠性。同时应控制片式电容器的焊接温度和时间, (一般为260℃/10秒)电容器安装时,应远离发热元件对于尺寸较大的电容器,不能用电容器引脚来安装,为防止在振动或冲击中下引线断裂或密封损坏,必要时还应设计夹持装置来固定安装时,还应尽量使电容器有标志的面露出来,以便观察。
  If the capacitor is a recently manufactured product and the solderability has met the requirements, tin dipping pretreatment is generally not required. If the storage time is long, the tin dipping treatment shall be carried out before use. The tin dipping treatment shall be controlled beyond the sealing 3.2 mm specified in the technical specification, and avoid melting of the sealing or disconnection between the lead and the electrode due to too long time or too high temperature. For chip capacitors, the flux with high activity and strong acid shall also be avoided to avoid unclean cleaning, penetration Corrosion and diffusion affect product reliability. When the capacitor is installed at the temperature of 260 ℃ / s, the lead of the capacitor should be fixed away from the welding temperature or the welding time of the capacitor. When it is necessary to install the capacitor, the lead should be fixed at 260 ℃ / s to prevent the capacitor from being damaged, The marked surface of the capacitor shall also be exposed as far as possible for observation.
  电解电容器是电子系统的最基础元件之一,是不可取代的电子元件。选择电解电容器必须按电子元器件的选择原则进行,要从整机所使用的环境条件、电性能要求、体积重量、可靠性要求及成本综合权衡。只有做到正确合适的选择和应用电解电容器,才能保证电子产品的质量和可靠性。
  Electrolytic capacitor is one of the most basic components of electronic system and is an irreplaceable electronic component. The selection of electrolytic capacitor must be carried out according to the selection principle of electronic components, and should be comprehensively weighed from the environmental conditions, electrical performance requirements, volume and weight, reliability requirements and cost of the whole machine. The quality and reliability of electronic products can only be guaranteed if electrolytic capacitors are correctly selected and applied.
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