如何计算PFC输出电容（how to calculate PFC output cap）

COUT : Two main criteria, the capacitance and the voltage rating, dictate the selection of the output capacitor. The value of capacitance is determined by the holdup time required for supporting the load after input ac voltage is removed. Holdup is the amount of time that the output stays in regulation after the input has been removed. For this circuit, the desired holdup time is approximately 16 ms. Expressing the capacitor value in terms of output power, output voltage, and holdup time gives the equation: COUT:两个主要的标准，电容容量和额定电压，决定了输出电容的选择。输入电压移除后，输出电容值由输负载支撑所需的持率时间决定。延迟是指输入被移除后，输出保持在规定状态的时间。对于这个电路，所需的持时大约是16ms。用输出来表示电容器的值功率、输出电压、持率时间为:


In practice, the calculated minimum capacitor value may be inadequate because output ripple voltage specifications limit the amount of allowable output capacitor ESR. Attaining a sufficiently low value of ESR often necessitates the use of a much larger capacitor value than calculated. The amount of output capacitor ESR allowed can be determined by dividing the maximum specified output ripple voltage by the inductor ripple current. In this design holdup time was the dominant determining factor and a 220-µF, 450-V capacitor was chosen for the output voltage level of 385 VDC at 250W


在实际应用中，由于输出纹波电压的存在，计算的最小电容值可能不够，规格限制了允许输出电容ESR的数量。经常获得足够低的ESR值需要使用比计算值大得多的电容器。输出电容ESR的数量允许通过将最大指定输出纹波电压在这个设计中滞留时间是占主导地位的决定因素和220 -µf 450 - v电容器选择的输出电压水平为385 VDC在250W