** Introduction **

Electronic transformers play an indispensable role in modern electronic equipment, from our daily use of mobile phone chargers to complex industrial equipment power supply, are inseparable from it. An in-depth understanding of the working principle and basic structure of electronic transformers helps us better understand the power supply system of electronic devices and the key significance of electronic transformers in them.

** II. Working principle **

1. ** Fundamentals of electromagnetic induction law **
- Electronic transformers work based on Faraday's law of electromagnetic induction. When a changing magnetic field passes through a closed circuit, an induced electromotive force is created in the circuit. The magnitude of this induced electromotive force is proportional to the rate of change of the magnetic flux passing through the circuit. For a simple coil, if an alternating current passes through it, an alternating magnetic field is generated around the coil.
- its mathematical expression for \ (E = - N \ frac {\ d Phi} {dt} \), including \ [E \] is the induction electromotive force, \ [N \] is the coil number of turns, \ \ Phi (\) is a magnetic flux, \ \) (t is time. The negative sign indicates that the direction of the induced electromotive force always obstructs the change of the magnetic flux, which is an embodiment of Lenz's law.
2. ** transformer voltage conversion principle **
- In an electronic transformer, there are primary and secondary windings. When alternating current \(I_1\) passes through the primary winding, an alternating magnetic field \(B\) is generated. This magnetic field will pass through the secondary winding and, according to the law of electromagnetic induction, generate an induced electromotive force \(E_2\) in the secondary winding.
- a primary winding circle number for \ (N_1 \), the secondary winding turns to \ (N_2 \), primary voltage to \ (V_1 \), secondary voltage for \ [V_2 \). According to the ideal transformer model (ignoring the loss), there is a relationship between the voltage ratio and the turns ratio \(\frac{V_2}{V_1}=\frac{N_2}{N_1}\). For example, if the \ (N_2 = \ frac {1} {2} N_1 \], then \ (V_2 = \ frac {1} {2} V_1 \). This is the basic principle of transformer voltage transformation.
3. ** Current and power relationship **
In an ideal transformer, according to the law of conservation of energy, the input power \(P_1 = V_1I_1\) is equal to the output power \(P_2=V_2I_2\). Therefore, \(\frac{I_2}{I_1}=\frac{N_1}{N_2}\), that is, the current is inversely proportional to the number of turns. When the transformer step-down (\ (V_2 < V_1 \)), \ (N_2 < N_1 \), then \ (I_2 > I_1 \).

** Three, basic structure **

1. ** Core **
- ** The role of the magnetic core ** : The magnetic core is an important part of the electronic transformer, which provides a low reluctance path for the magnetic field. By concentrating the magnetic field inside the magnetic core, the utilization efficiency of the magnetic field can be improved, and the magnetic coupling between the primary and secondary windings can be enhanced.
- ** Common core materials ** :
- ** Ferrite core ** : It has the characteristics of high permeability and low loss (especially at high frequency). The ferrite core has a higher resistivity, which helps to reduce eddy current losses. It is suitable for high frequency electronic transformers, such as widely used in switching power supplies. Ferrite cores with different compositions (such as manganese zinc ferrite, nickel zinc ferrite) are suitable for different frequency ranges and power levels.
- ** Silicon steel core ** : Often used in low-frequency transformers. The magnetic permeability of silicon steel sheet is high and the cost is relatively low. It is made of silicon steel sheet laminated, this laminated structure can reduce eddy current loss. Silicon steel core is mainly used in transformers at 50Hz or 60Hz mains frequency, such as traditional linear power transformers.
2. ** winding **
- ** Primary winding ** : It is the winding connected to the input power supply. The number of turns is determined according to the input voltage, output voltage requirements and core characteristics. The amount of current in the primary winding depends on the input voltage and the input power of the transformer.
- ** Secondary winding ** : connected with the load, used to output the transformed voltage. The ratio of the number of turns in the secondary winding to the number of turns in the primary winding determines the ratio of the voltage transformation. When making windings, factors such as the material, thickness and number of turns of the wire should be considered.
- ** Winding Material and design ** :
- In high-frequency transformers, the current tends to flow on the wire surface due to the skin effect. In order to reduce the increase in resistance caused by this effect, a litz wire consisting of multiple strands of thin wire is often used. For low-frequency transformers, the main consideration is the current carrying capacity of the wire, and a single-strand wire with a larger diameter is generally selected.
3. ** Insulation material **
- In electronic transformers, insulation is used to isolate the primary and secondary windings and the electrical connection between the windings and the magnetic core. This is to prevent leakage and short circuit phenomenon.
- Common insulating materials include polyester film, polyimide film, etc. These materials have good insulation properties, mechanical properties and heat resistance. In the process of transformer production, the thickness and quality of insulation materials directly affect the safety and reliability of the transformer.

The working principle of the electronic transformer is based on the law of electromagnetic induction, and the voltage transformation function is realized through the coordination of the primary and secondary windings and the action of the magnetic core. Its basic structure includes parts such as magnetic core, winding and insulation material, each of which has an important impact on the performance of electronic transformers.