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All colleagues unite and focus their efforts to write a new chapter of developmentWhat is power adapter ripple? How can ripple generation be controlled?
所属分类： Industry News
发布时间：2020-06-09
First, let’s explain what ripple actually is and why power adapters generate it. A power adapter manufacturer will provide a brief overview.
The ripple in a power adapter can indeed be observed using appropriate equipment—namely, an oscilloscope. On the oscilloscope, you can see that when the power adapter is operating, the voltage exhibits slight fluctuations, somewhat resembling ripples on water; this phenomenon is referred to as “ripple.” So, does the presence of ripple in a power adapter indicate something good or bad?
In fact, even the best power adapters exhibit some level of ripple—some more, some less. Generally speaking, the higher the output voltage, the greater the ripple. Ripple is simply an AC component superimposed on a DC voltage; when filtering is imperfect, this AC component remains, resulting in observable ripple.
In general, for 5V products, the power‑supply ripple is typically kept below 100 mV, while for 12V products, the maximum ripple is usually around 120 mV. So how can we control the generation of ripple in a power adapter?
First, we can increase the inductance and the output capacitor to improve filtering. Simply put, the current ripple across an inductor is inversely proportional to its inductance value, while the power‑adapter ripple is inversely proportional to the output capacitor’s capacitance. Therefore, by increasing both the inductance and the capacitance, we can reduce the power‑adapter ripple.
Secondly, we can connect a capacitor C or an RC network in parallel with the diode. The primary purpose of this is to suppress high-frequency oscillations; however, the appropriate values must be determined through repeated experimentation, as an improperly chosen value may produce the opposite effect. Therefore, this approach should be adopted with great care.
Third, using an LDO filter—this approach is the most effective, but it also incurs the highest cost and results in relatively high power consumption.
Fourth, add a first-order LC filter; the LC filter provides excellent suppression of ripple in the power adapter.