DC-bias-voltage dependence of degradation of aluminum electrolytic capacitors

Attention has been paid to reliability-related issues for dc-link capacitors such as monitoring methods, power-loss estimation, and ageing tests. The degradation of the capacitors depends on their operating condition including temperature, ripple current, and dc-bias voltage, which has a strong influence on failures as well. In design stages of power converters, it is desirable to know the relation between the degradation and electrolytic parameters. This paper makes an intensive discussion on the voltage dependence of the degradation of a small aluminum electrolytic capacitor with an ageing test and a leakage-current measurement. The ageing test reveals that a higher dc-bias voltage brings a faster increase in ESR but results in a slower drop in capacitance in a range within the rated voltage. This result implies that either capacitance or ESR cannot be a unique indicator of the lifetime. Attention should be paid both to the ESR and to the capacitance when one monitors the capacitor condition. On the other hand, more than the rated voltage leads a rapid degradation of the capacitor, which can be confirmed by a leakage-current measurement instead of the ageing test.     

Means of Eliminating Electrolytic Capacitor in AC/DC Power Supplies for LED Lightings

This paper proposes two methods of reducing the storage capacitance in the ac/dc power supplies for light emitting diode (LED) lighting. In doing so, film capacitors can be adopted instead of electrolytic capacitors to achieve a long power supplies’ lifetime. The voltage ripple of the storage capacitor is intentionally increased to reduce the storage capacitance. The method of determining the storage capacitance for ensuring that the boost power factor correction converter operates normally in the whole input voltage range is also discussed. For the purpose of further reducing the storage capacitance, a method of injecting the third harmonic current into the input current flow is proposed. While ensuring that the input power factor is always higher than 0.9 to comply with regulation standards such as ENERGY STAR, the storage capacitance can be reduced to 65.6% of that with an input power factor of 1. A 60-W experimental prototype is built to verify the proposed methods.      

有机电解质片式钽电容器稳定性的提高

新一代信息技术的发展不仅要求有机固体电解质片式钽电容器的等效串联电阻(ESR)小,更需要在严酷环境中使用时电容量、ESR和漏电流保持稳定。影响钽电容器稳定性的影响因素很多,其中界面稳定性是关键因素之一。为此,在此类电容器生产中引入一种新的界面预处理方法,即在介质氧化膜表面涂敷硅烷偶联剂预涂层,抑制介质氧化膜-聚合物界面的劣化。经过高低温、浪涌电压和125℃-2000 h寿命测试,静电容量、漏电流和ESR的稳定性有明显改善。试验结果表明,该界面预处理技术是制造高稳定性高压有机钽电容器非常有效的方法。     

Prognostics of aluminum electrolytic capacitors using artificial neural network approach

In this work, an effort is being made to monitor the condition of in-circuit aluminum electrolytic capacitor using artificial neural network (ANN). Recent industrial surveys on the reliability of power electronic systems shows that most of faults occur due to the wear out of aluminum electrolytic capacitors and thermal stress is the major cause for its parametric degradation. The condition of target capacitors can be estimated by monitoring variation in equivalent series resistance (ESR) from the initial pristine state value. ANN is used to estimate ESR of pristine and weak target capacitors at the test conditions. The data set for training and testing of proposed back-propagation trained artificial neural network are experimentally obtained from the developed test bed. Using the test bed, target capacitors are subjected to different operating frequency and temperature in the output section of DC/DC buck converter circuit to determine the effect of variation in electrical and thermal stress on ESR value. After off-line training, the proposed ANN is implemented using National Instruments LabVIEW software. A low cost microcontroller is programmed for real time data acquisition of target capacitors and the serial transmission of acquired dataset to the LabVIEW software installed at host computer. The performance of the proposed method is evaluated in real time by comparing the resulting ESR with the experimental values of in-circuit target capacitors. The proposed ANN, once trained properly, can be used for different circuits and in different operating conditions because of its generalization capability.     

适合集成开关电容DC-DC变换器的浮地电容倍增器

针对在集成电路中制作大容量电容器的困难，提出了一种利用电流传输器提高集成电容器容量的方法，称之为连续可变浮地电容倍增器。分析了电容倍增的机理，建立了相应的关系式，在此基础上对用此浮地电容构成的一阶滤波器和开关电容DC-DC变换器进行了理论分析和PSPICE仿真。结果表明，利用电流传输器的阻抗变换作用，可使小容量的电容等效变换为较大容量的浮地电容，从而便于开关电容DC-DC变换器实现全单片集成。     

导电聚合物（PEDOT）浆料在钽电容器生产中应用

通过采用浸渍导电聚合物浆料和原位聚合方法制备聚合物钽电容器,并对比电容器电性能,研究导电聚合物浆料对聚合物钽电容器电性能的影响。实验结果表明导电聚合物浆料可以提高电容器的耐压性能,即产品有较高的击穿电压值,但是产品的容量引出率和ESR恶化。     

Loss-Free Balancing Circuit for Series Connection of Electrolytic Capacitors Using an Auxiliary Switch-Mode Power Supply

Most of today's power converters such as three-phase variable-speed drives, uninterruptible power systems, welding converters, and telecom and server power supplies are based on voltage-source converters equipped with bulky dc-link electrolytic capacitors. To be able to handle full dc bus voltage, the dc bus capacitor is arranged as series-connected electrolytic capacitors rated at lower voltage. An electrolytic capacitor, however, is not an ideal capacitor. It has significant leakage current that strongly depends on the capacitor temperature, voltage, and ageing conditions. To compensate large dispersion of the leakage current and ensure acceptable sharing of the total dc bus voltage among the series-connected capacitors, a passive balancing circuit is often used. Drawbacks of the ordinary passive balancing circuit, such as size, significant losses, and standby consumption are discussed in this paper. An active loss-free balancing circuit, which utilizes an auxiliary switch-mode power supply (SMPS) to equalize the capacitor voltages, is proposed. The capacitors midpoint (MP) is connected to the SMPS via two devices; namely a current injection device and a compensation device. The current injection device injects current into the capacitors MP, while the compensation device sinks the difference between the capacitor leakage currents and the injected current. As a result, the capacitor voltages are controlled and maintained in the desired ratio. The proposed balancing technique is theoretically analyzed and experimentally verified on a laboratory setup. The results are presented and discussed.      

纽扣型液体双电层电容器的研制

极化电极、电解液和隔离膜是液体双电层电容器的主要组成部分。实验分析了它们对电容器电性能的影响。在此基础上 ,试制出的模型电容器的电容量 C超过 1F,漏电流 IL (2 V偏压下 )小于 0 .5 m A,等效串联电阻 ESR低于 10Ω。     

DC-Link Harmonics of Three-Phase Voltage-Source Converters Influenced by the Pulsewidth-Modulation Strategy—An Analysis

DC-link current harmonics are the predominant factor to be considered for dimensioning dc capacitors in three-phase pulsewidth-modulation (PWM) voltage-source converters. In this paper, an analysis of the dc-link current harmonics applying a double Fourier series is derived. The analytical results for the dc-link current spectra of continuous and discontinuous PWMs are presented and compared with measurement results taken from a converter test setup. A good match between theoretically expected and actually obtained experimental results can be stated. Moreover, characteristic differences between the investigated modulation strategies regarding their dc-link current spectra become evident.     

Charging–discharging characteristics of a wound aluminum polymer capacitor

This study characterized aluminum polymer capacitors, especially when they are charging and discharging. Tests were conducted under various conditions. The following environments were considered: three high-temperature conditions, two high temperature/high humidity conditions, and room temperature. Various operating conditions were also considered, such as charging–discharging, operating, and storage. The test results showed that the capacitance of the wound polymer aluminum capacitor degraded with charging–discharging at low temperature. At lower temperatures, this characteristic accelerated but was mitigated with a dry electrolyte. The degraded capacitances partially recovered when the capacitors were stored at a high temperature. These characteristics were not observed for a conventional liquid aluminum capacitor. This unreported special characteristic of polymer aluminum capacitors should be considered when designing systems such as power electronics. Polymer capacitors are known for their high reliability, especially at high temperatures. At low temperatures, however, the charging–discharging characteristic should be carefully considered. This paper reports on this characteristic of polymer capacitors for consideration by industries.     

Optimization of word-line booster circuits for low-voltage flashmemories

Two word-line booster circuits, which output a word-line voltage for reading dash memory data, are analyzed and optimized. A capacitor-switched booster circuit outputs a voltage higher than the supply voltage by switching the connection state of one of more boosting capacitors with the load capacitor from parallel to series. The optimum number of capacitors and capacitance per boosting capacitor are obtained as a function of the voltage ratio of the required high voltage to the supply voltage. The operation current consumed by the boosting operation is also analytically derived. In addition, another booster circuit-Dickson charge-pump circuit-is optimized under the condition to maximize the output current at a high word-line voltage. Characteristics of the booster circuits are compared, and the selection of booster circuit for low-voltage flash memory is discussed     

Output capacitor stability study on a voltage-mode buck regulator using system-poles approach

System poles approach for pulsewidth-modulated (PWM) dc/dc converters analysis is developed making use of the sensitivity matrix. It combines both small-signal analysis for stability assessment and large-signal analysis for wide operating condition. This paper is particularly focused in stability study on the output capacitor capacitance and equivalent series resistance (ESR) in a buck regulator using the system poles approach. Using the system-poles approach in the output capacitance example it is found that unstable operating point possibly exists between two stable operating points for some conditions. Tends of stable-to-unstable or unstable-to-stable are observed by the z-domain poles movement with different changing circuit parameters. Making use of these tends, it is exemplified that the unstable operating point can be stabilized. This paper shows that output capacitance and ESR are critical to the stability and stability can be improved by modification on the output capacitor.     

Lanthanide (Tb)-doped HfO/sub 2/ for high-density MIM capacitors

A high-density metal-insulator-metal (MIM) capacitor with a lanthanide-doped HfO/sub 2/ dielectric prepared by physical vapor deposition (PVD) is presented for the first time. A significant improvement was shown in both the voltage coefficient of capacitance (VCC) and the leakage current density of MIM capacitor, yet the high capacitance density of HfO/sub 2/ dielectrics was maintained by achieving the doping of Tb with an optimum concentration in HfO/sub 2/. This technique allows utilizing thinner dielectric film in MIM capacitors and achieving a capacitance density as high as 13.3 fF//spl mu/m/sup 2/ with leakage current and VCC values that fully meet requirements from year 2005 for radio frequency (RF) bypass capacitors applications.     

Profiling generation lifetime in an MOS capacitor using a multistep constant-capacitance technique

This paper describes a method to obtain the depth profile of generation lifetime in a semiconductor using a MOS capacitor. The capacitance is kept constant at a number of values in deep depletion, and the resulting gate voltage transient measured. This consists of a series of ramps. The profile of the generation lifetime is obtained from the slopes of the ramps and the values of capacitance through which the capacitor is stepped.     

Bulk lifetime determination using an MOS capacitor

A simple method is described for the determination of minority carrier lifetime from the large-signal response time of an MOS capacitor in deep inversion. The method consists of monitoring the change of MOS capacitance as a function of time. A graph is presented to expedite easy extraction of lifetime from the transient waveform.     

Temperature rise measurement for power-loss comparison of an aluminum electrolytic capacitor between sinusoidal and square-wave current injections

DC-link capacitors are a major factor of degrading reliability of power electric converters because they usually have a shorter lifetime and higher failure rate than those of semiconductor devices or magnetic devices. Characteristics of the capacitors are usually evaluated by a single sinusoidal current waveform. However, actual current flowing out of the converter into the capacitor is a modulated square current waveform. This paper provides experimental comparison of the power loss dissipated in an aluminum electrolytic capacitor between sinusoidal and square-wave current injections. Power loss is estimated by temperature rise of the capacitor. Experimental results confirm that power losses of the square-wave current injection were always lower than those of the sinusoidal current injection by 10–20%. Moreover, the power losses of the square-wave current injection can be estimated by a synthesis of fundamental and harmonic currents based on the Fourier series expansion, which brings a high accuracy less than 1% when more than fifth harmonic current is introduced. This comparison will be useful for estimating power loss and life time of electrolytic capacitors.     

An approximation algorithm to improve capacitance matching in the design of SC filters

A critical issue in the design of switched-capacitor (SC) filters is the capacitance matching, because the filter coefficients depend on capacitance ratios. The most successful design method to achieve an accurate capacitance matching employs a parallel arrangement of identical unit capacitors to implement each filter capacitor. However, this procedure can be directly applied only if the filter coefficients can be written as rational numbers, since each capacitor is implemented as an integer number of unit capacitors in parallel. This paper presents a systematic procedure, with low computational effort, to approximate the filter coefficients by integer ratios causing acceptable errors in the filter frequency response, whereas keeping the total number of unit capacitors small, in order to save die area. This procedure was applied in the design of a sixth-order SC band-pass filter, which has been fabricated in a 0.35 μm CMOS technology. The fabricated filter occupies an area of 0.913 mm², exhibits low sensitivity to fabrication process deviations and has an output dynamic range of 79.2 dB.     

Lifetime prediction of aluminum electrolytic capacitors in LED drivers considering parameter shifts

The electrolytic capacitor (Al-Cap) is widely considered as one of the reliability-critical components in LED driver applications. A realistic lifetime prediction of Al-Caps would be beneficial to the sizing of capacitors to fulfill a specified design lifetime. This paper investigates the impact of electrolytic capacitor parameter shifts on the LED driver performance and the capacitor reliability. The operation condition, degradation, and tolerance are considered as the main reasons that deviate the parameters from nominal values. A method to model the degradation of Al-Cap parameter is introduced as well. In the case study of a flyback LED driver for street lighting, the contribution of parameter shifts to the electrical performance of LED drivers and Al-Cap core temperature is evaluated based on both theoretical analysis and simulation. A quantitative comparison of the estimated lifetime of Al-Cap in the LED driver is given with and without the consideration of capacitor parameter shifts within the service life. The proposed method enables a more realistic way for electrolytic capacitor lifetime prediction in LED drivers, which would otherwise have the risk of overestimation.     

智能型动态功率因数监测与补偿系统

描述了基于单片机为控制核心的低电压动态功率因数监测与补偿系统。该系统将MOC3041与可控硅BT137结合作为补偿电容投入的控制开关,同时利用MOC3041内部的过零比较器来实现延时控制作用,成功解决了补偿电容投入时可能产生的电流冲击问题。在软件上采用PWM技术,控制"开关"通断时间及频率来改变补偿电容投入时的等效电容量,使补偿电容量连续可调。该电容补偿技术很好地实现了对当前电路稳定、可靠、精确的检测和控制。     

Effective Radii of On-Chip Decoupling Capacitors

Decoupling capacitors are widely used to reduce power supply noise. On-chip decoupling capacitors have traditionally been allocated into the white space available on a die or placed inside the rows in standard cell circuit blocks. The efficacy of on-chip decoupling capacitors depends upon the impedance of the power/ground lines connecting the capacitors to the current loads and power supplies. A design methodology for placing on-chip decoupling capacitors is presented in this paper. A maximum effective radius is shown to exist for each on-chip decoupling capacitor. Beyond this effective distance, a decoupling capacitor is ineffective. Depending upon the parasitic impedance of the power distribution system, the maximum voltage drop seen at the current load is caused either by the first droop (determined by the rise time) or by the second droop (determined by the transition time). Two criteria to estimate the minimum required on-chip decoupling capacitance are developed based on the critical parasitic impedance. In order to provide the required charge drawn by the load, the decoupling capacitor has to be charged before the next switching cycle. For an on-chip decoupling capacitor to be effective, both effective radii criteria should be simultaneously satisfied.