How to Prevent Ripple Generation in Switching Power Supplies
Following the switch of SWITCH, the current in inductor L also fluctuates up and down within the effective value of the output current. So there will also be a ripple at the output end with the same frequency as SWITCH, which is generally referred to as ripple. It is related to the capacity and ESR of the output capacitor.
How to suppress the generation of ripple in switch mode power supply? Our goal is to reduce the output ripple to a tolerable level. The fundamental solution to achieve this goal is:
Generation of Ripple in Switching Power Supply
Our goal is to reduce the output ripple to a tolerable level, and the fundamental solution to achieve this goal is to avoid the generation of ripple as much as possible. Firstly, we need to clarify the types and causes of ripple in the switching power supply.
Following the switch of SWITCH, the current in inductor L also fluctuates up and down within the effective value of the output current. So there will also be a ripple at the output end with the same frequency as SWITCH, which 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 a switching power supply, ranging from tens to hundreds of KHz.
In addition, SWITCH generally uses bipolar transistors or MOSFETs. Regardless of which one is used, there will be a rise time and a fall time when it is turned on and off. At this point, a noise with the same frequency or odd multiples of the SWITCH rise and fall time will appear in the circuit, usually in the tens of MHz range. At the moment of reverse recovery, the equivalent circuit of diode D is a series connection of resistance, capacitance, and inductance, which can cause resonance and generate noise frequencies of several tens of MHz. These two types of noise are generally called high-frequency noise, and their amplitude is usually much larger than ripple.
If it is an AC/DC converter, in addition to the two types of ripple (noise) mentioned above, there is also AC noise, which is the frequency of the input AC power supply, around 50-60Hz. There is also a type of common mode noise, which is caused by the equivalent capacitance generated by the power devices of many switching power supplies using enclosures as heat sinks. As I am engaged in automotive electronics research and development, I have less exposure to the latter two types of noise, so I am not considering them at the moment.
