★ The diode D1&D3 work, D2&D4 cut off, the current flows through the load resistance RL in a loop and charge the capacitor C up when U2 in the positive half circuitand its value exceeding the voltage Uc which is parallel connected in the two terminals of 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.
★ 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.
2.1 测试温升计算电容寿命/Life time of capacitor at testing temperature condition
计算寿命公式/ Formula for calculating lifetime ：
适用公司/ Corporation suited：Fcon 、KSC、TL、TEAPO、CapXon
2.2 测试纹波电流计算电容寿命/Life time of capacitor at testing ripple current condition
计算寿命公式/ Formula for calculating lifetime：
2.2.1 直接测量电容纹波电流/Direct measure of E-cap ripple current
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 switching MOSFET Q1. 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.
2.2.2 利用低通和高通滤波电路测量纹波电流/Measurement via low pass or high pass filter
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.
The bandwidth of low pass filter is 0~wc（wc=1/RC）， and >wc in high pass filter.
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.
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）