1. Selection of △B is too high, the core heat (no-load check whether the core is hot);
2. The selection of △B is not high, the high frequency loss of the core itself is large, and the core is hot (no-load check whether the core is hot);
3. Line current density is too high and winding heat. If no-load core is not hot, it should be winding current density is too high, of course, excluding the high frequency harmonics caused by distribution parameters.
4. The current density of windings and the selection of magnetic core (△B) are not suitable, and both windings and magnetic cores are hot.
5. In boost transformer (output high voltage), high frequency oscillation of distribution parameters results in both core and winding heating.
6. Design transformer with high power density but improper heat dissipation measures, such as planar transformer, should have good heat dissipation measures. Current density should be selected according to power and volume: small power relative surface area, large heat conduction path, short current density can be selected larger; high power, long heat conduction path, small circuit density should be selected. After high frequency, attention should be paid to the general 200 kHz or more. The empirical formula of temperature rise (T=[total loss of transformer mW/transformer surface area (CM ^ 2)] ^ 0.833 planar transformer surface area volume is smaller than the traditional value of large iron loss/surface area, so higher B can be chosen.