★ 當U2為正半周并且數(shù)值大于電容兩端電壓Uc時，二極管D1和D3管導通，D2和D4管截止，電流一路流經(jīng)負載電阻RL，另一路對電容C充電。當Uc>U2，導致D1和D3管反向偏置而截止，電容通過負載電阻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U2為負半周幅值變化到恰好大于Uc時，D2和D4因加正向電壓變?yōu)閷顟B(tài)，U2再次對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D2和D4變?yōu)榻刂?，C對RL放電，Uc按指數(shù)規(guī)律下降；放電到一定數(shù)值時D1和D3變?yōu)閷ǎ貜蜕鲜鲞^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.測試方法/TestMethod

　　2.1 測試溫升計算電容壽命/Life time of capacitor at testing temperature condition

　　計算壽命公式/ Formula for calculating lifetime ：

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

　　2.2 測試紋波電流計算電容壽命/Life time of capacitor at testing ripple current condition

　　計算壽命公式/ Formula for calculating lifetime：

　　2.2.1 直接測量電容紋波電流/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，其充電時間受到低頻交流輸入影響，而放電時間則是受到開關(guān)管Q1的高頻影響。即A點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點處所測試出電流為電容C1的低頻紋波電流（IL）；B點受到高頻開關(guān)Q1的影響，頻率一般為100KHz，故B點所測試出的電流為電容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.

　　目前對電容紋波計算方法定義為/ 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量紋波電流/Measurement via low pass or high pass filter

　　對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，電流的測量必須串一個電流檢測電阻去獲得，而且低頻紋波電流和高頻紋波電流應分別測量。

　　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.

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

　　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.

低頻紋波電流測試圖

　　★ 在檢測電阻上并接一個RC（0.1uF、1K5）電路，（如下圖所示），用有效值表測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）

高頻紋波電流測試圖