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1. If △B is selected too high, the core is hot (check whether the core is hot without load).

2. The △B selection is not high, the high-frequency loss of the magnetic core itself is large, and the magnetic core is hot (check whether the magnetic core is hot without load).

3. The wire current density is too large and the winding is hot. If the no-load magnetic core is not hot, then the winding current density should be too large. Of course, it is excluded that the magnetic core is heated due to the high frequency harmonics generated by the distributed parameters.

4. The winding current density and the magnetic core △B are not suitable, and both the winding and the magnetic core are hot.

5. In the step-up transformer (output high voltage), the distributed parameter is large and the high-frequency oscillation is generated to make the magnetic core and the winding heat.

6. The design transformer has a high power density but the heat dissipation measures should not be when the temperature of the transformer rises. For example, a planar transformer must have good heat dissipation measures. The current density selection is selected according to power and volume: low power relative to large surface area, short heat conduction path, short current density can be selected larger ; The power is large, the heat conduction path is long, and the circuit density should be small. After the high frequency is generally above 200kHz, attention should be paid to the adhesion effect and the appropriate wire diameter can be selected. The current is large, the stranded wire can be used. The temperature rise empirical formula △T=[total transformer loss mW/transformer surface area (CM^2)]^0.833 The surface area-to-volume ratio of a planar transformer is large. The iron loss/surface area value is smaller than the traditional one, so a higher △B can be used.