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High Frequency Transformer Design Common Method Introduction
Apr 05, 2018

     

             High Frequency Transformer Design Common Method Introduction


The high-frequency chain inverter technology replaces the bulky power frequency transformers in traditional inverters with high-frequency transformers, which greatly reduces the size and weight of the inverter. High-frequency transformers are an important part of high-frequency-chain hardware circuit design. High-frequency transformers are power transformers whose operating frequency exceeds mid-frequency (10kHz). They are mainly used as high-frequency switching power transformers in high-frequency switching power supplies, and also used in high-frequency inverter power supplies and high-frequency inverter welding machines for high-frequency inverters. Transform the power transformer.


High-frequency transformers are non-standard parts, and their specifications vary. There is no naming standard. The so-called model is simply a sign for the manufacturer to distinguish between classifications. It is usually necessary to design custom processing.

  Designing a high frequency transformer should start with the core first. Switching power transformer cores are mostly soft magnetic materials used under low magnetic fields. They have high magnetic permeability, low coercive force, and high resistivity. High magnetic permeability, when a certain number of turns of the coil, through a small exciting current can withstand high applied voltage, so under the output of a certain power requirements, can reduce the magnetic core volume. Core coercive force is low, hysteresis area is small, the iron loss is also less. With high resistivity, the eddy current is small and the iron loss is small. The ferrite material is a complex oxide sintered body, which has a high resistivity and is suitable for use at high frequencies. However, the Bs value is relatively small and is often used in switching power supplies.

 

The design of high-frequency transformers generally uses two methods: The first is to find the product AP of the core window area AW and the effective cross-sectional area Ae of the core AP (AP = AW × Ae, called the core area product), According to the AP value, look up the table to find out the required magnetic material number;

The second is to find the geometric parameters, look up the table to find the core number, and then design.

In the process of high-frequency transformer design, attention should be paid to:

 

1) During the transient process, high-frequency chain leakage inductance and distributed capacitance will cause inrush current, peak voltage, and top oscillation of the pulse, which will increase the loss. In severe cases, the switch tube will be damaged. At the same time, when the number of turns of the output winding is large and the number of layers is large, the influence of the distributed capacitance should be taken into account. The reduction of the distributed capacitance is advantageous in suppressing the interference of the high-frequency signal to the load. It is difficult for the same transformer to reduce the distributed capacitance and leakage inductance at the same time, and the appropriate capacitance and inductance should be guaranteed according to different working requirements.


2) In the design, the magnetic flux density in the magnetic core should not reach saturation at the time of maximum output power, so as to avoid distortion in large signals.



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