纹波电压，英文ripple voltage，也叫涟波电压。正如涟波的形象比喻，标示电线上电压的像水波一样的波动。
好奇的一个问题是，纹波都是怎么产生的。控制什么东西，都要从源头和控制两部分着手。
google来了下面一段话：
Ripple is often random, but sometimes other components in the circuit can cause this noise to occur. For example, a relay or motor switching can often times cause a sudden fluctuation in the voltage. Much like disturbing the water level in a pond. The more current the other component uses, the bigger the ripple effect. 【来自一个工程师的博客】
纹波通常是一个比较随机的值，但是多是电路中的其它一些元件导致的这些噪声（纹波其实也是噪声，我们想要的之外的都是噪声）。比如，电路中的继电器和马达通常会引起电流的一个突变。接下来发生的事，就像是往水塘里扔了一个石子。同时，电路中其它元件需要的电流越大，导致的纹波也就越多。
While all of these benefits are noteworthy, perhaps the greatest motivation for using the current doubler rectifier is the reduced ripple current seen by the output capacitors. In some sense, the current doubler rectifier can be thought of as a two-phase, interleaved synchronous buck. As shown in Figure 2, maximum ripple current cancellation for a two-phase synchronous buck occurs when each phase is operating at 50 percent duty cycle. However, because the volt-seconds applied to the transformer primary must be equal for each half of the power transfer cycle, the current doubler is limited to a maximum duty cycle of 50 percent per phase, whereas the two-phase synchronous buck can operate at greater than 50 percent duty cycle per
phase.【来自TI】
对两相的buck Converter最大的纹波抑制，发生在相角为buck converter an-off周期50%的时候。
Ripple current is the AC component of an applied source (often a switched-mode power supply) whose frequency may be constant or varying. Certain types of capacitors, such as electrolytic tantalum capacitors, usually have a rating for maximum ripple current (both in frequency and magnitude). This ripple current can cause damaging heat to be generated within the capacitor due to the current flow across resistive imperfections in the materials used within the capacitor, more commonly referred to as equivalent series resistance (ESR). For example electrolytic tantalum capacitors are limited by ripple current and generally have the highest ESR ratings in the capacitor family, while ceramic capacitors generally have no ripple current limitation and have some of the lowest ESR ratings.【来自wiki】