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Since I need knowledge about transformers, I couldn't find any relevant content in this forum, so I looked for some on the Internet. I don't know if it will be useful, but the moderator will decide. Transformers The main functions of a transformer are:: voltage conversion ； Impedance transformation ； isolation ； Voltage stabilization (magnetic saturation transformer), etc. The commonly used core shapes of transformers generally include E-type and C-type cores. 1. Basic principles of transformer When a sinusoidal AC voltage U1 is applied to both ends of the primary coil, there is an alternating current I1 in the wire and an alternating magnetic flux ф1 is generated. It passes through the primary coil and the secondary coil along the core to form a closed magnetic circuit. Mutual inductance potential U2 is induced in the secondary coil, and ф1 will also induce a self-induction potential E1 on the primary coil. The direction of E1 is opposite to the direction of the applied voltage U1 but has a similar amplitude, thus limiting the size of I1. In order to maintain the existence of magnetic flux ф1, a certain amount of power consumption is required, and the transformer itself also has certain losses. Even though the secondary is not connected to a load at this time, there is still a certain current in the primary coil. This current is called "no-load current". If the secondary is connected to a load, the secondary coil will generate current I2, and thus generate magnetic flux ф2. The direction of ф2 is opposite to ф1, which cancels each other out, reducing the total magnetic flux in the core, thereby reducing the primary self-inductance voltage E1. As a result, I1 increases. It can be seen that the primary current is closely related to the secondary load. When the secondary load current increases, I1 increases and ф1 also increases, and the increased part of ф1 just supplements the part of the magnetic flux offset by ф2 to keep the total magnetic flux in the core unchanged. If the loss of the transformer is not considered, it can be considered that the power consumed by the secondary load of an ideal transformer is the electrical power obtained by the primary from the power supply. The transformer can change the secondary voltage as needed by changing the number of turns in the secondary coil, but it cannot change the power the load is allowed to consume. 2. Loss of transformer When the primary winding of the transformer is energized, the magnetic flux generated by the coil flows in the iron core. Because the iron core itself is also a conductor, an electric potential will be induced on a plane perpendicular to the magnetic lines of force. This electric potential forms a closed loop on the cross section of the iron core and generates a current, which is like a vortex, so it is called "eddy current". This "eddy current" increases the loss of the transformer and increases the temperature rise of the transformer's core heating transformer. The loss caused by "eddy current" is called "iron loss". In addition, a large amount of copper wire is needed to wind the transformer. These copper wires have resistance. When the current flows through, the resistance will consume a certain amount of power. This loss is often consumed as heat. We call this loss "copper loss". Therefore, the temperature rise of the transformer is mainly caused by iron loss and copper loss. Since the transformer has iron loss and copper loss, its output power is always less than the input power. For this reason, we introduce an efficiency parameter to describe this, eta = output power/input power. 3. Transformer Materials To wind a transformer, we must have a certain understanding of the materials related to the transformer. For this reason, I will introduce this knowledge here. 1. Core material: The core materials used in transformers mainly include iron sheets, low silicon sheets, and high silicon sheets. Adding silicon to steel sheets can reduce the conductivity of the steel sheets and increase the resistivity. It can reduce eddy currents and reduce losses. We usually call the steel sheet with silicon added as silicon steel sheet. The quality of the silicon steel sheet used in the transformer has a great relationship. The quality of the silicon steel sheet is usually expressed by the magnetic flux density B. Generally, the B value of black iron sheet is 6000-8000, low silicon sheet is 9000-11000, and high silicon sheet is 12000-16000. 2. The commonly used materials for winding transformers include enameled wire, sand-covered wire, silk-covered wire, and the most commonly used enameled wire. The requirements for wires are good electrical conductivity, sufficient heat resistance of the insulating paint layer, and certain corrosion resistance. Under normal circumstances, it is best to use Q2 model high-strength polyester enameled wire. 3. Insulating materials In winding transformers, insulating materials must be used for isolation between coil frame layers and windings. Generally, transformer frame materials can be made of phenolic cardboard, polyester film or telephone paper can be used for isolation between layers, and yellow wax cloth can be used for isolation between windings. 4. Impregnated materials: After the transformer is wound, the last step is to impregnate it with insulating paint, which can enhance the mechanical strength of the transformer, improve its insulation performance, and extend its service life. Under normal circumstances, cresol varnish can be used as the impregnating material. And this: A transformer is a device that converts AC voltage, current and impedance. When AC current flows through the primary coil, AC magnetic flux is generated in the iron core (or magnetic core), causing voltage (or current) to be induced in the secondary coil. A transformer consists of an iron core (or magnetic core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary coil, and the remaining windings are called secondary coils. 1. Classification by cooling method: Dry type (self-cooling) transformer, oil-immersed (self-cooling) transformer, fluoride (evaporative cooling) transformer. Classified by moisture-proof method: Open transformer, potted transformer, sealed transformer. Classified by core or coil structure: Core type transformer (slice core, C-type core, ferrite core), shell-type transformer (slice core, C-type core, ferrite core), toroidal transformer, metal foil transformer. Classification by power phase number: Single-phase transformer, three-phase transformer, multi-phase transformer. Classified by use: Power transformer, voltage regulating transformer, audio transformer, medium frequency transformer, high frequency transformer, pulse transformer. 2. Characteristic parameters of power transformer 1. Working frequency The core loss of the transformer has a great relationship with the frequency, so it should be designed and used according to the frequency of use. This frequency is called the working frequency. 2. At the rated power, under the specified frequency and voltage, the transformer can work for a long time without exceeding the output power with specified temperature rise. 3. The rated voltage refers to the voltage allowed to be applied to the coil of the transformer, which shall not exceed the specified value during operation. 4. Voltage ratio refers to the ratio between the primary voltage and the secondary voltage of the transformer. There is a difference between no-load voltage ratio and load voltage ratio. 5. When the secondary of the no-load current transformer is open circuit, there is still a certain current in the primary. This part of the current is called no-load current. No-load current consists of magnetizing current (generating magnetic flux) and iron loss current (caused by core losses). For a 50Hz power transformer, the no-load current is basically equal to the magnetizing current. 6. No-load loss refers to the power loss measured on the primary side when the secondary side of the transformer is open-circuited. The main loss is the core loss, followed by the loss (copper loss) caused by the no-load current on the primary coil copper resistance. This part of the loss is very small. 7. Efficiency refers to the percentage of the ratio of secondary power P2 to primary power P1. Generally, the greater the power rating of the transformer, the higher the efficiency. 8. Insulation resistance indicates the insulation performance between the coils of the transformer and between each coil and the iron core. The insulation resistance is related to the performance of the insulating material used, temperature and humidity. 3. Characteristic parameters of audio transformers and high-frequency transformers 1. Frequency response refers to the characteristics of the secondary output voltage of the transformer changing with the operating frequency. 2. Passband: If the output voltage of the transformer at the intermediate frequency is U0, the frequency range when the output voltage (the input voltage remains unchanged) drops to 0.707U0 is called the passband B of the transformer. 3. Primary and secondary impedance ratio. The primary and secondary impedances of the transformer are connected to appropriate impedances Ro and Ri, so that the primary and secondary impedances of the transformer match. Then the ratio of Ro and Ri is called the primary and secondary impedance ratio. In the case of impedance matching, the transformer works in the best state and has the highest transmission efficiency.