For the old bird of power supply, more contact design will form a set of unique techniques and habits. With the growth of experience, this will form a virtuous circle. For novices, it is difficult to find a suitable entry point, let alone form such a benign change. But the problem that hinders the progress of novices will be solved. This series of articles take flyback power design as an entry point, deeply study the design method of this power supply and explain its principle in detail, and cultivate good design habits.

In order to achieve a more obvious demonstration effect, the parameters used in this article are exaggerated. Input requirements: AC90 ~ 275V, output 5V ~ 40A. A 200W flyback power supply (such a large power supply may not be able to pass EMC, because leakage inductance and flyback mode problems make high-power flyback EMC more sad). Because the power supply voltage is not high, the current is large, and the secondary rectifier loss is large, it is estimated that the design efficiency is 90% according to this method. The higher the output voltage, the better the efficiency.

Next, talk about the power design software to be used.

1. SMPS Cal: This is a power calculation tool for comprehensive evaluation, such as what topology to choose, how large cores to use, capacitance capacity, current RMS, peak value and so on. Let your heart have a rough idea first.

2. saber 2007 is a simulation software, which is used to simulate the principle problems when designing power supply. Open-loop simulation is the most popular simulation.

3. PExprt: This is a transformer design software in ansys. It is easy to use and has a high degree of coincidence with the actual situation.

This article mainly explains the electrolytic capacitor, and uses saber for appropriate auxiliary explanation. The latter difficulty will be the transformer part.

The chip is BO5269D. The frequency of this chip is 65K. Let's use tools to see how many cores are needed. Because there is no special requirement, we use EE cores to design this power supply.

Calculated is 30,000 cubic millimeters, this is a reference design, not a real stereotype, so we chose three magnetic cores in the Yellow standard. Now I have a general understanding of the core in my heart.