How to prevent the occurrence of switching power supply ripple
Following the switch of SWITCH, the current in the inductor L also fluctuates up and down the effective value of the output current. Therefore, there will also be a ripple with the same frequency as SWITCH at the output end. This is generally referred to as ripple. It is related to the capacity and ESR of the output capacitor.
How to suppress the generation of switching power supply ripple? Our ultimate goal in the generation of switching power supply ripple is to reduce the output ripple to a tolerable level. The most fundamental solution to achieve this goal is:
Generation of switching power supply ripple
Our goal is to reduce the output ripple to a tolerable level. The most fundamental solution to achieve this goal is to try to avoid the generation of ripples. First, we must clearly understand the types and causes of switching power supply ripples.
Following the switch of SWITCH, the current in the inductor L also fluctuates up and down the effective value of the output current. Therefore, there will also be a ripple with the same frequency as SWITCH at the output end. This is generally referred to as ripple. It is related to the capacity and ESR of the output capacitor. The frequency of this ripple is the same as that of the switching power supply, which is tens to hundreds of KHz.
In addition, SWITCH generally uses bipolar transistors or MOSFETs. No matter which one is used, there will be a rise time and fall time when it is turned on and off. At this time, a noise with the same frequency or an odd multiple of the SWITCH rise and fall time will appear in the circuit, usually tens of MHz. Similarly, at the moment of reverse recovery of diode D, its equivalent circuit is a series connection of resistors, capacitors and inductors, which will cause resonance and generate noise with a frequency of tens of MHz. These two types of noise are generally called high-frequency noise, and their amplitudes are usually much larger than ripple.
In the case of an AC/DC converter, in addition to the two ripples (noise) mentioned above, there is also AC noise. The frequency is the frequency of the input AC power supply, which is about 50 to 60 Hz. There is also a kind of common mode noise, which is caused by the equivalent capacitance generated by the power devices of many switching power supplies that use the shell as a heat sink. Since I am engaged in automotive electronics research and development, I have less exposure to the latter two types of noise, so I will not consider them for the time being.
