Introduction to what factors need to be considered when selecting a switching power supply
For engineers, the selection of switch mode power supplies is a process that needs to be completed for every power supply solution. It may seem like a multiple-choice question, but before making a final decision, engineers need to consider many factors. Of course, the first thing we think of at the top of the list is the issue of cost. In today's article, we want to clarify that in the process of selecting switch mode power supplies, in addition to cost, we need to pay attention to some essential factors when choosing the most suitable power module.
We need to be careful and consider many rules regarding the selection of switch power modules. For example, the nominal value of the stabilizing wire is 1A, which refers to the policy at 25 degrees Celsius. However, assuming the equipment operates at 50 degrees Celsius, the nominal value of the stabilizing wire may be lower than 1A, and the margin for the solution at this temperature needs to be slightly larger. Similarly, the 1mH of an inductor is not always 1mH. It is at 1kHz. Assuming you use it at 1MHz, the value of the 1mH inductor sent by the manufacturer is not 1mH. Due to the significant impact of scattered capacitance in the inductor coil at 1M, some of the inductance's effects will be offset. The insertion loss IL of the filter is 25dB, which is the time when MHz Rs/RL=50 ohms (source impedance and load impedance). However, in practice, it is difficult to achieve impedance to meet this requirement in the application of our filter, so a 25dB insertion loss will result in a significant loss. Magnetic beads, capacitors, diodes, resistors... all have similar rules. Next, let's talk about the rules for selecting switch power modules, apart from cost. There are various topological structures for power modules, including flyback, forward, push-pull, half bridge, and full bridge, each of which has advantages in certain characteristic aspects due to its diverse principles.
Here we will explain the application rules of several typical topological constructions. The primary issue is the flyback power supply, which does not discharge during the charging period in one switching cycle. Due to this characteristic, its constant care and ripple characteristics are difficult to achieve excellent results. Although it can be handled with the help of large energy storage capacitors, the fundamental disadvantage is ultimately a hard flaw. Intellectual deficiency can be compensated for through hard work, but when encountering critical problems, it cannot overcome a certain hurdle. There are also issues such as high leakage inductance, but its benefits include a simple circuit, low cost, small size, no need to add magnetic reset windings, and a wider input voltage scheme. It is precisely because of this that it accounts for over 70% of the total power supply market.
