1. Introduction to Transformer Principles

A transformer, as its name suggests, is an electronic power device designed to change voltage levels. It operates on the principle of Faraday's law of electromagnetic induction, enabling the transformation of alternating current voltages. Typically, a transformer consists of key components such as a primary coil, an iron core, and a secondary coil. Transformers can facilitate matching and conversion of input and output currents, voltages, and impedances, while also providing physical isolation between the primary and secondary circuits. Depending on the voltage ratio between the primary and secondary windings, transformers are classified into types such as step-down transformers, step-up transformers, and isolation transformers.

2. Based on the operating frequency, transformers are classified into low-frequency transformers and high-frequency transformers.

The frequency of electricity used in our daily life and production is 50 Hz, and we refer to this type of alternating current as low-frequency AC. When a transformer operates at this frequency, it’s called a low-frequency transformer—or, alternatively, a power-frequency transformer. These transformers are typically bulky and less efficient. Their iron cores are constructed by stacking mutually insulated silicon steel laminations, while the primary and secondary coils are wound using enameled wire. Notably, the voltage across each coil is directly proportional to its number of turns.

In addition, some transformers operate at frequencies ranging from tens to hundreds of kilohertz—these are known as high-frequency transformers. Unlike conventional transformers that rely on iron cores, high-frequency transformers typically use magnetic cores instead. As a result, high-frequency transformers are compact in size, feature fewer turns in their primary and secondary coils, and boast high efficiency.

3. Differences and similarities between high-frequency and low-frequency transformers.

High-frequency transformers typically operate at frequencies ranging from tens to hundreds of kilohertz. These transformers use magnetic cores, whose primary material is manganese-zinc ferrite— a substance that minimizes eddy currents and reduces losses at high frequencies, resulting in high efficiency. In contrast, low-frequency transformers, which operate domestically at 50 Hz, rely on soft magnetic metal cores. The use of thin, laminated silicon steel sheets significantly cuts down on eddy current losses—but even so, their core losses remain higher compared to those of high-frequency transformers.

For transformers delivering the same power output, high-frequency transformers are significantly smaller in size and generate less heat compared to low-frequency ones. That’s why many modern consumer electronics and networking device power adapters today rely on switch-mode power supplies, with the high-frequency transformer being the core component of these systems. The basic principle involves first converting the incoming AC power into DC, then using transistors like bipolar junction transistors or field-effect transistors to step up the frequency. This high-frequency signal is subsequently transformed by the high-frequency transformer, followed by another rectification stage to produce a stable DC output. Finally, additional control circuits ensure that the output voltage remains consistent and reliable.