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Analysis of Causes for Ripple of Switching Power Supply
Mar 12, 2018


         Analysis of Causes for Ripple of Switching Power Supply

Switching power supply design often occurs when the noise, which is the output ripple, then the switching power supply ripple causes what? Since the existence of ripples will affect the normal operation of the switching power supply, we must suppress the generation of ripples, but we only understand and analyze the causes of the ripples, we may find a solution, this article is for everyone to introduce the switch The cause of power ripple was analyzed. For specific conditions, please see the following specific analysis.

With SWITCH switching, the current in inductor L also fluctuates above and below the rms value of the output current. Therefore, a ripple with the same frequency as SWITCH will also appear at the output. The ripple is generally referred to as this. It is related to the output capacitor's capacity and ESR. The frequency of this ripple is the same as the switching power supply, which is tens to hundreds of KHz.


In addition, the general choice of SWITCH bipolar transistor or MOSFET, no matter what, will have a rise time and fall time in its leading deadline. At this point in the circuit there will be noise at the same frequency as the rise time of the switch or at an odd frequency, typically tens of megahertz. At the instant of reverse recovery, the resistance and capacitance of the equivalent circuit are connected in series with the inductor, which will cause resonance and the noise frequency will also be tens of megahertz. These two types of noise are often referred to as high-frequency noise, and the amplitude is usually much larger than the ripple.


In the case of an AC/DC converter, in addition to the above two types of ripple (noise), there is AC noise, and the frequency is the frequency of the input AC power, which is about 50 to 60 Hz. There is also a common-mode noise because power devices of many switching power supplies use the case as a heat sink, resulting in an equivalent capacitance.


What are the requirements of the switching power ripple? Mainly to look at the design of the product and the demand for the load is now a good point of power supply, output ripple voltage control in the following 200mV, less than 50mV If a small signal analog and digital control circuits, especially analog circuits, the power supply ripple is very demanding Clean, for other applications, such as LED drive power, ripple is a little bit of no impact

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