★ 當(dāng)U2為正半周并且數(shù)值大于電容兩端電壓Uc時(shí)，二極管D1和D3管導(dǎo)通，D2和D4管截止，電流一路流經(jīng)負(fù)載電阻RL，另一路對(duì)電容C充電。當(dāng)Uc>U2，導(dǎo)致D1和D3管反向偏置而截止，電容通過負(fù)載電阻RL放電，Uc按指數(shù)規(guī)律緩慢下降。

　　★ ThediodeD1&D3 work, D2&D4 cut off, the current flows through the load resistance RL in a loop and charge thecapacitorC up when U2 in the positive halfcircuitand its value exceeding the voltage Uc which is parallel connected in the twoterminalsof capacitor. When Uc exceeds U2, and causes the diode D1&D3 cut off, the capacitor discharge through the load resistance RL and Uc decline slowly according to the principle of index function.

　　★ 當(dāng)U2為負(fù)半周幅值變化到恰好大于Uc時(shí)，D2和D4因加正向電壓變?yōu)閷?dǎo)通狀態(tài)，U2再次對(duì)C充電，Uc上升到U2的峰值后又開始下降；下降到一定數(shù)值時(shí)D2和D4變?yōu)榻刂?，C對(duì)RL放電，Uc按指數(shù)規(guī)律下降；放電到一定數(shù)值時(shí)D1和D3變?yōu)閷?dǎo)通，重復(fù)上述過程。

　　★ As the same reason , when U2 in the negative half circuit and the amplitude is even changed to exceed Uc ,the diode D2&D4 work due to the positive voltage and U2 charge capacitor C up again. Uc start to decline when it’s voltage rise to the peak value of U2 and to a certain value , the diode D2&D4 cut off , the capacitor C discharge to RL, Uc decline according to the principle of index function again. When the discharge to a certain value, the diode D1&D3 work again and the cycle repeats.

　　2.測(cè)試方法/TestMethod

　　2.1 測(cè)試溫升計(jì)算電容壽命/Life time of capacitor at testing temperature condition

　　計(jì)算壽命公式/ Formula for calculating lifetime ：

　　適用公司/ Corporation suited：Fcon 、KSC、TL、TEAPO、CapXon

　　2.2 測(cè)試紋波電流計(jì)算電容壽命/Life time of capacitor at testing ripple current condition

　　計(jì)算壽命公式/ Formula for calculating lifetime：

　　2.2.1 直接測(cè)量電容紋波電流/Direct measure of E-cap ripple current

開關(guān)電路中電容紋波電流分析

　　C1為buck電容，其充電時(shí)間受到低頻交流輸入影響，而放電時(shí)間則是受到開關(guān)管Q1的高頻影響。即A點(diǎn)受到低頻交流輸入影響，頻率為交流頻率的2倍，100Hz左右，故A點(diǎn)處所測(cè)試出電流為電容C1的低頻紋波電流（IL）；B點(diǎn)受到高頻開關(guān)Q1的影響，頻率一般為100KHz，故B點(diǎn)所測(cè)試出的電流為電容C1的高頻紋波電流（IH）。

　　C1 is the buck capacitor, its charge time lies on the low frequency Vac input, and the discharge time influenced by the high frequency of switchingMOSFETQ1. The frequency of position A, lying on the Vac input, is doubled, about 100Hz. And the current flowed through just is the low frequency current of C1; similarly, the frequency of position B, lying on the Q1, is about 100 KHz, and the current is high frequency.

　　目前對(duì)電容紋波計(jì)算方法定義為/ The test method defined in our company at present is：

　　2.2.2 利用低通和高通濾波電路測(cè)量紋波電流/Measurement via low pass or high pass filter

　　對(duì)于輸入大容量的電容，有低頻（100HZ）和高頻（開關(guān)頻率，如100KHZ）兩種電流流過，電流的測(cè)量必須串一個(gè)電流檢測(cè)電阻去獲得，而且低頻紋波電流和高頻紋波電流應(yīng)分別測(cè)量。

　　For bulk capacitor, both low frequency （100HZ） and high frequency （switching frequency, say 100 KHz） current are flowing. The current shall be measured with a current sense resistor. As the low and high frequency ripple shall be measured separately.

低通濾波電路

高通濾波電路

　　低通濾波電路的帶寬為0~wc（wc=1/RC），高頻濾波電路帶寬則為>wc。

　　The bandwidth of low pass filter is 0~wc（wc=1/RC）， and >wc in high pass filter.

　　★ 在檢測(cè)電阻上并接一個(gè)RC（1k5、0.1uF）電路，（如下圖所示）用有效值表測(cè)量0.1uF兩端的有效電壓，即可得低頻紋波電流值，此時(shí)高頻成分已被濾除。

　　Add an RC （1K5, 0.1uF） across the sense resistor, measure rms voltage across 0.1uF; this will filter out the high frequency, leaving the 100Hz ripple current.

低頻紋波電流測(cè)試圖

　　★ 在檢測(cè)電阻上并接一個(gè)RC（0.1uF、1K5）電路，（如下圖所示），用有效值表測(cè)1K5電阻兩端的有效值電壓，根據(jù)I=U/R即可獲得高頻紋波電流值，此時(shí)低頻成分已被濾除。

　　Add a CR （0.1uF, 1K5） across the sense resistor, measure rms voltage across 1K5; this will filter out the low frequency, leaving the switching frequency ripple current. Calculate with I =U/R. （Note: R is 0.1 ohm, not 1K5）

高頻紋波電流測(cè)試圖