High Frequency Transformer Design Principles


  When designing a high frequency transformer, 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 the transient process of transmission, leakage inductance and distributed capacitance will cause surge current and peak voltage, as well as top oscillation, resulting in increased loss. Usually the leakage inductance of the transformer is controlled as 1% to 3% of the primary inductance.

  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, between layers, and between turns.

  Distributed capacitance--the capacitance formed between the turns of the transformer winding, between the upper and lower layers of the same winding, between different windings, and between the winding and the shielding layer is called distributed capacitance.

  Primary winding--the primary winding should be placed in the innermost layer, so that the wire length of each turn of the primary winding of the transformer can be the shortest, so that the entire winding wire is the least, which effectively reduces the distribution of the primary winding itself capacitance.

  Secondary winding - After the primary winding is wound, (3-5) layers of insulating pads should be added and then the secondary winding should be wound. In this way, the capacitance of the distributed capacitance between the primary winding and the secondary winding can be reduced, and the insulation strength between the primary and secondary windings can be increased, meeting the requirements of insulation withstand voltage.

  Bias winding - whether the bias winding is wound between the primary and secondary, or wound on the outermost layer, is related to whether the adjustment of the switching power supply is based on the secondary voltage or the primary voltage.

  High-frequency transformer is a power transformer whose working frequency exceeds intermediate frequency (10kHz). It is mainly used as high-frequency switching power transformer in high-frequency switching power supply, and also used as high-frequency inverter in high-frequency inverter power supply and high-frequency inverter welding machine. power transformer. According to the working frequency, it can be divided into several grades: 10kHz-50kHz, 50kHz-100kHz, 100kHz-500kHz, 500kHz-1MHz, and above 1MHz. When the transmission power is relatively large, the power device generally adopts IGBT, because the IGBT has the off-current tailing phenomenon, so the operating frequency is relatively low; when the transmission power is relatively small, MOSFET can be used, and the operating frequency is relatively high.