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High frequency transformer working principle analysis
Feb 18, 2018

       

         High frequency transformer working principle analysis


What is the working principle of high-frequency transformers? The high-frequency power transformer is a power transformer whose working frequency exceeds mid-frequency (10khz). It is mainly used as high-frequency switching power transformer in high-frequency switching power supply, and also used in high-frequency inverter power supply and high-frequency inverter welding machine for high frequency. Inverter power transformer. The number of turns of each winding coil of the high frequency transformer determines the output voltage. The design method of power transformers with different working frequencies is not the same, and it should be self-evident.


High-frequency power transformer design principles


High-frequency power transformer as a product, naturally with the properties of goods, so the design principles of high-frequency power transformers and other commodities, is to achieve specific performance under the specific conditions of use in the pursuit of the best performance and price ratio. Sometimes it may be performance and efficiency, and sometimes it may be price and cost. Nowadays, light, thin, short, and small have become the development direction of high-frequency power supplies, emphasizing reducing costs. Product costs include not only material costs, production costs, but also R&D costs and design costs. Therefore, in order to save time, according to past experience, provide some reference data for the copper loss ratio of the core loss of the high frequency power transformer, the leakage inductance and the ratio of the excitation inductance, the loss ratio of the primary and secondary windings, the current density, and the degree of window filling. , winding wire and structure recommend some solutions,

 

High-frequency transformer principle design principle

In the design of high frequency transformers, the leakage inductance and distributed capacitance of the transformer must be minimized because the high frequency transformer in the switching power supply transmits a high frequency pulse square wave signal. During transmission transients, leakage inductance and distributed capacitance can cause surge currents and spike voltages, as well as top oscillations, causing increased losses. The leakage inductance of the transformer is usually controlled to 1% to 3% of the primary inductance.

 

The leakage inductance of the primary coil—the leakage inductance of the transformer is caused by the incomplete coupling of the magnetic flux between the primary coil and the secondary coil, and between the layers.

 

Distributing Capacitance—The capacitance formed between the winding windings of the transformer, between the upper and lower layers of the same winding, and between different windings, and between the windings and the shielding layer is called distributed capacitance.

 

Primary winding—The primary winding should be placed in the innermost layer, so that the length of each winding of the primary winding of the transformer is the shortest, so that the entire winding has the minimum number of wires, which effectively reduces the distribution of the primary winding itself. capacitance.

 

Secondary Winding ---- After the primary winding is completed, it is necessary to add (3 to 5) layers of insulating mat liners to wind the secondary windings. This reduces the capacitance of the distributed capacitance between the primary winding and the secondary winding, and also increases the dielectric strength between the primary and secondary, and meets the requirements for insulation withstand voltage.

Bias Winding—The bias winding is wound between the primary and the secondary or the outermost layer. The adjustment of the switching power supply depends on the secondary voltage or the primary voltage.

 

High frequency transformer should have the function


The high-frequency power transformer has three complete functions: power transmission, voltage conversion and isolation. There are two ways of power delivery. The first is the transmission method of transformer power. The voltage applied to the primary winding generates a magnetic flux change in the core, causing the secondary winding to induce a voltage so that the electric power is transmitted from the primary side to the secondary side. The second is the power transmission mode of the inductor. The input power of the primary winding causes the magnetic core to become energized and become magnetic energy, and then demagnetizes the secondary winding to induce the voltage and turn it into electrical energy for release to the load.


The voltage conversion is accomplished by the turns ratio of the primary and secondary windings. Regardless of the power transfer method, the voltage conversion ratios of the primary and secondary sides are equal to the turns ratio of the primary winding and the secondary winding. As long as the turns ratio is not changed, the voltage conversion is not affected.


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