Introduction to the basic knowledge of low frequency transformers

A low-frequency transformer refers to a transformer used in low-frequency circuits. The iron core of the low frequency transformer is generally made of silicon steel sheet, and the common iron core shapes are E-shaped, C-shaped and annular, as shown in the figure below.

The advantage of the E-shaped core is low cost, but the disadvantage is that the air gap in the magnetic circuit is large, the efficiency is low, and the electrical noise is large during operation. The C-shaped iron core is composed of two C-shaped iron cores with the same shape. Compared with the E-shaped iron core, the air gap in the magnetic circuit is smaller and the performance is improved. The annular iron core is wound by cold-rolled silicon steel strip, there is no air gap in the magnetic circuit, the leakage magnetic field is extremely small, and the electrical noise is small during operation.
Common low frequency transformers include power transformers and audio transformers, as shown in the figure below.

The function of the power transformer is to step up or step down the mains voltage. Among them, the step-down power transformer that reduces the voltage is the most common. Some mobile phone chargers and external power supplies of small recorders all use step-down power transformers. This kind of transformer has a large number of primary winding turns and is connected to a 220V AC voltage; while the secondary winding has a small number of turns and outputs a lower AC voltage. In some high-quality power amplifiers, toroidal power transformers are often used.

Audio transformers are used in audio signal processing circuits, such as audio amplifier circuits of radios and recorders, which often use audio transformers to transmit signals. When an audio transformer is added between the two circuits, the audio transformer can transmit the signal of the previous stage circuit to the latter stage circuit to the greatest extent.