Hifh frequency transformer is a power transformer whose operating frequency exceeds the intermediate frequency (10kHz). It is mainly used as hf switching power transformer in hf switching power supply, as well as hf inverter power supply transformer in hf inverter welding machine. According to the working frequency, it can be divided into several levels: 10kHz ~ 50kHz, 50kHz ~ 100kHz, 100kHz ~ 500kHz, 500kHz ~ 1MHz and above. The transmission power is relatively large, the operating frequency is relatively low; The transmission power is relatively small, the operating frequency is relatively high. In this way, there are the difference of working frequency and power supply, and the design method of power transformer with different working frequency is different.