DC、AC和RIPPLE的区别是什么呢？

freezing616

各位大虾，有知道的说说》在电源（开关电源）网络分析中，一般都要求把输出端的电压变化限制在DC+AC+RIPPLE=5%的范围内。请各位大虾指导，这里的DC、AC和RIPPLE分别指什么，或者说是分别由什么原因引起的？

freezing616

dc：电源平面的阻抗会产生压降
ac:瞬态电流？
ripple:瞬态电流？

BlueIC

dc就是指直流电压，也就是说你的LDO的输出标称值；
AC就是说输出电压上叠加的交流电压的幅度，周期性的正弦波，频率一般比较低，比如来自市电的50Hz的影响而导致输出有AC值。
ripple是纹波，是由于负载变动而导致的不规律的高频波动，频率比较高，而且波形不规律。

harsun

DC+AC+RIPPLE=5%
一般器件电源输入端的指标要求有三个：直流电压值，噪声和纹波，你说的应该是跟这三个指标对应的：
DC：表示电源输入端的直流电平值，可以用万用表直接测试得到，不过这里应该指偏离理想电压值的幅度；
AC：应该表示电源输入的噪声，是全带宽范围内，非周期性的交流干扰信号，是所有干扰或者不稳定因素综合产生的结果；
RIPPLE：电源纹波，严格来讲也是属于AC的范畴，是周期性的，带宽在测试中一般取20M以内。它最常见的来源是开关电源的开关噪声；

freezing616

3# BlueIC
谢谢你的回答！我做的是开关电源的那一块，可能一开始问题描述的不是太清楚。刚看到4楼的见解和你的有点出入，希望大虾能继续参与讨论。

gysgys

顶一下，还有没有别的答案，期待中.................................

freezing616

继续顶起！期待深度讨论。

Chilton

This is not a very scientific design spec. The design requirement of the total output voltage variation should come from the application.

For example, if the supply rail can tolerate +/- 10% total variation (4.5~5.5V for a 5.0V rail, and 3.7~3.6 V for a 3.3V rail), a 50% variation is allocated to the power supply, you can then assume the simplified total output voltage variation is 5% (the other half can be allocated to PCB trace voltage drop etc).

The simplified total output voltage variation has three components:

DC error: contributed by the accuracy of the reference voltage and output voltage sensing circuit. For example, most of the switching mode ICs today use 1.5% internal voltage reference, if your feedback resistors use 0.5% accuracy precision resistors, you can roughly estimate your DC accuracy to be 1.5%.

AC error: contributed by the finite input/output DC impedance. Ideally you will have infinite input impedance and 0 output impedance, but this ideal circuit will cost you so much that it will never be practical. All real circuits have finite input/output impedance therefore suffer from line regulation and load regulation. This is your AC error.

Ripple voltage: this is the voltage variation of the output filter capacitor. It has two components: ESR voltage drop and ripple current component. You can calculate the ripple voltage if you know the ESR of your output cap and your peak-2-peak ripple current/output cap size.