Field analysis of TWT HVPS transformer and HV module

The role of a high power density DC power supply is very important in designing a compact and high efficiency TWT microwave amplifier. In order to fabricate a compact power supply, it is necessary to reduce transformer volume by increasing switching frequency of the power supply. However, a step-up ratio of the transformer in the high voltage DC power supply could not be indefinitely increased due mainly to self-resonance by stray capacitance and leakage inductance. Therefore, the pulse transformer should be carefully designed to fulfill its function in the power supply. A high frequency and high voltage pulse transformer is designed, fabricated, and tested. Switching frequency of the transformer is 100 kHz. Input and output voltages of the transformer are 250 V and 4 kV, respectively. Normal operation power of the transformer is 3 kW. Maximum allowed volume of the transformer is 400 cm³. The transformer is installed in a metal box that has nominal operation temperature of 85 degree centigrade. The transformer and other high voltage components in the box are molded with silicon RTV that has a very low thermal conductivity. Calculated and measured results of various parameters such as transformer loss, temperature rise, leakage inductance, distributed capacitance, and hysterisis characteristics are presented. In addition, field analysis results obtained with ANSYS code for the transformer and the HV module are also presented.