A transformer is a device that uses the principle of electromagnetic induction to transform AC voltage. Its main components include a primary coil, a secondary coil, and an iron core.

In the electronics profession, transformers are often seen, and the most common ones are used in power supplies for voltage conversion and isolation.

Simply put, the voltage ratio of the primary and secondary coils is equal to the turns ratio of the primary and secondary coils. Therefore, if you want to output different voltages, you can change the turns ratio of the coils.

According to the working frequency of the transformer, it can generally be divided into low-frequency transformers and high-frequency transformers. For example, in daily life, the frequency of power-frequency alternating current is 50Hz, and we call the transformers working at this frequency low-frequency transformers; and high-frequency transformers The operating frequency can reach several tens of kHz to several hundreds of kHz.

The low-frequency transformer and the high-frequency transformer with the same output power, the volume of the high-frequency transformer is much smaller than that of the low-frequency transformer.

The transformer is a relatively large component in the power supply circuit. If you want to make the volume small while ensuring the output power, a high-frequency transformer must be used, so high-frequency transformers are used in switching power supplies.

The working principles of high-frequency transformers and low-frequency transformers are the same, and both work on the principle of electromagnetic induction, but in terms of production materials, the materials used for their "cores" are different.

The iron core of a low-frequency transformer is generally formed by stacking many silicon steel sheets, while the iron core of a high-frequency transformer is composed of high-frequency magnetic materials (such as ferrite). (So ​​the iron core of the high frequency transformer is generally called the magnetic core)

In the DC regulated power supply circuit, the low-frequency transformer transmits a sine wave signal.

In the switching power supply circuit, the high-frequency transformer transmits a high-frequency pulse square wave signal.

The low-frequency transformer is generally on the circuit symbol, and the primary coil has only one winding. The symbol you often see is probably like this:

As for high-frequency transformers, on the circuit symbol, you may find that some high-frequency transformers actually have two coils on the primary side?

In fact, there are not two primary coils. There is only one primary coil and the other is an auxiliary coil. The "auxiliary coil" actually belongs to the secondary coil. The reason why it is called the auxiliary coil is because it plays an auxiliary role in the circuit.

The auxiliary coil serves the circuit connected to the primary coil. The auxiliary coil is in the primary and can provide a voltage source and feedback signal for protection of the transformer. Through the feedback function of the auxiliary coil, the internal power supply can be stabilized.

In addition, when the output of the secondary coil is overloaded, the excessive current will lead to insufficient carrying capacity of the secondary coil, which will cause the output voltage of the secondary coil to drop, and the output voltage of the auxiliary coil will also drop. vibration, thus protecting the switch tube.

At rated power, the ratio between the output power of the transformer and the input power is called the efficiency of the transformer,

When the output power of the transformer is equal to the input power, the efficiency is 100%. In fact, such a transformer does not exist. Because of the existence of copper loss and iron loss, the transformer will have a certain loss.

What is copper loss?

Because the transformer coil has a certain resistance, when the current passes through the coil, part of the energy will become heat. Since the transformer coil is wound with copper wire, this loss is also called copper loss.

What is iron loss?

The iron loss of the transformer mainly includes two aspects: one is the hysteresis loss, and the other is the eddy current loss; the hysteresis loss means that when the alternating current passes through the coil, a magnetic line of force will be generated through the iron core, and the molecules inside the iron core will rub against each other to generate heat. This consumes part of the electric energy; because the magnetic lines of force pass through the iron core, the iron core will also generate an induced current, which is also called eddy current because the current is eddy current, and the eddy current loss will also consume part of the electric energy.