The dielectric loss of a high-voltage/high-frequency transformer for a switching power supply is investigated. Measurements were made on a transformer designed to operate in a 100 kHz power supply. The voltages of the primary, secondary, and tertiary windings are 60 V, 950 V, and 1200 V, respectively. The results show that the dielectric loss constitutes a large part of loss at high frequency and that thermal runaway can occur unless some precautions are taken in the design. In particular, the amount of dielectric loss depends very strongly on the type of insulating materials used.
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