Three-pronged approach to reduce switching power supply ripple

　　Three-pronged approach to reduce switching power supply ripple

　　1. Energy storage inductor. The larger the Q value of the energy storage inductor at the operating frequency, the better. Many people only pay attention to the inductance. In fact, the impact of the Q value is much greater. As long as the inductance meets the requirements, it is allowed to fluctuate within a wide range.

　　2. Filter capacitor. The ESR and ESL of filter capacitor are very important parameters. The lower the better. It is far from enough to pursue capacity alone. Of course, under the premise of meeting sufficiently low ESR and ESL, a larger capacity is better. The filter capacitor of the switching power supply is preferably a combination of X7R or X5R capacitor and tantalum electrolytic capacitor. If the ripple is slightly relaxed, Y5V capacitor and tall aluminum electrolytic capacitor (low ESL type) can be used.

　　3. PCB design. The PCB design of the switching power supply is very important. When the first two conditions are met, if the ripple parameters still cannot reach the values ​​stated in the manual, the problem can be confirmed to be on the PCB. The design of the sampling and filtering circuits of the switching power supply chip is very particular. The PCB distribution parameters will lead to adjustment errors or poor filtering efficiency. In severe cases, it may even cause self-excitation (usually occurs under a specific load intensity), so it has to be checked. The principle is that the sampling circuit and the filtering circuit should be as close to the switching power supply IC as possible, and the PCB routing should not be too long or too thin. Similar energy storage inductors have the same principle, but the impact is slightly smaller. Unfavorable layout and routing are equivalent to reducing the Q value of the inductor.

　　Finally, it should be said that due to the different internal circuit designs of switching power supply ICs, the ripple indicators are also different. In most cases, higher switching frequencies are easier to obtain lower ripples, but the price and requirements for peripheral components are relatively higher. Therefore, it is necessary to make reasonable choices based on needs and just use enough. Otherwise, unnecessary costs will be incurred. Careful reading and understanding of the device manual is the first step.