The Key Player in Switching Power Supplies: Transformers

In the complex world of switching power supplies, the transformer is like a quiet but indispensable hero, playing a crucial role. Today, let's delve deep into the mysteries of transformers in switching power supplies.

一、The Core Role of Transformers

The transformer undertakes the critical task of voltage transformation in switching power supplies. It's like a precise magician, ingeniously converting the input voltage through the principle of electromagnetic induction to the output voltage we need. Whether it's reducing a high voltage to suit various electronic devices, such as converting 220V mains power to 5V for charging mobile phones, or boosting a low voltage to meet specific requirements, like raising 12V to 48V in certain industrial applications, the transformer can accomplish this mission with extremely high precision and efficiency.

二、Revelation of the Working Principle

The operation of the transformer is based on the classic physical principle of electromagnetic induction. The formula is: , where  is the induced electromotive force,  is the power supply frequency,  is the number of winding turns, and  is the maximum magnetic flux.

When an alternating current flows merrily through the primary winding of the transformer, it creates a constantly changing alternating magnetic field around it. This magnetic field is like an enthusiastic messenger that passes through the elaborately designed iron core and then induces a voltage in the secondary winding. By ingeniously adjusting the turns ratio of the primary and secondary windings  (where  is the number of primary turns and  is the number of secondary turns), we can achieve various voltage transformations as we wish according to the formula , just like holding the magic wand of electricity.

三、Diverse Types to Meet Different Demands

1. High-Frequency Transformers

On the high-frequency stage of switching power supplies, high-frequency transformers are the well-deserved protagonists. With the characteristic of high-frequency operation, typically with a working frequency reaching tens of kHz or even hundreds of kHz, it successfully reduces the volume and weight of the transformer significantly. For instance, compared to traditional low-frequency transformers, the volume can be reduced by more than 50%, making significant contributions to the thinning and lightweight design of electronic devices and achieving high power density.

2. Planar Transformers

Planar transformers have emerged with their unique planar structure. This innovative design not only reduces the profile height, often only a fraction of the thickness of traditional transformers, but also brings excellent efficiency, which can reach over 95%, and superior thermal performance with a significantly reduced thermal resistance, becoming the favorite in high-density integrated circuit designs.

四、Careful Selection of Core Materials

The choice of core materials is one of the keys to determining the performance of the transformer.

1. Ferrites

With its high resistivity (typically above  Ω·m) and low loss (loss tangent less than 0.001 at high frequencies), it becomes the first choice for high-frequency switching power supply transformers. It can maintain stable performance in the high-frequency alternating magnetic field and effectively reduce energy loss.

2. Iron Powder Cores

Although slightly inferior in terms of loss, it possesses better magnetic permeability (up to over 100) and higher saturation magnetic flux density (typically above 1T), and can also perform well in certain specific application scenarios.

五、Meticulous Design for Excellence

1. Turns Calculation

The precise calculation of turns is the cornerstone of transformer design. Based on the input and output voltages and the operating frequency, engineers calculate the number of turns of the primary and secondary windings using the formula