Three elements of low ripple power supply
2022-09-04

The following are the three elements of a low ripple power supply:

1. Energy storage inductance. The larger the Q value of the energy storage inductance at the working frequency, the better. Many people only pay attention to the inductance. In fact, the influence of Q value is much larger. As long as the inductance meets the requirements, it is allowed to fluctuate in a large range.

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

3. PCB design. The PCB design of the switching power supply is very important. If the ripple parameter still fails to reach the value specified in the manual when the first two conditions are met, the problem can certainly be attributed to the PCB. The sampling and filter circuit design of the switching power supply chip is very careful. The PCB distribution parameters will lead to adjustment errors or poor filter efficiency. In serious cases, it may even lead to self excitation (generally under specific load intensity), so we have to check. The principle is that the sampling circuit and the filter circuit should be as close to the switching power supply IC as possible, and the PCB wiring should not be too long or too thin. Similar energy storage inductors have the same principle, but the impact is slightly small, and the unfavorable layout and wiring is equivalent to reducing the Q value of the inductor.

Finally, because the internal circuit design of the switching power supply IC is different, the ripple index is also different. In most cases, the high switching frequency is easy to obtain a lower ripple, but the price and requirements for the external components are relatively higher. Therefore, it is necessary to choose reasonably according to the needs, and enough is enough, otherwise unnecessary costs will be paid. Careful reading and understanding of the device manual is the first step.