High voltage power supplies for radar applications are investigated, which are subjected to high frequency pulsed load (above 100 kHz) with stringent specifications (regulation < 0.01%, efficiency >85%, droop < 0.5 V/micro-sec.). As good regulation and stable operation requires the converter to be switched at much higher frequency than the pulse load frequency, transformer poses serious problems of insulation failure and higher losses. The solution to this problem as a single stage converter is very difficult. In converters operating at high voltage and high frequency, the insulation failure of high voltage transformer is very common. Skin and proximity effect result in higher power losses. Because of high turns ratio, the winding capacitance results in delays and current spikes. Hence a two-stage converter has been proposed. It isolates the HV transformer from high frequency requirement of the regulation. Its block diagram is shown in the following figure. One stage of it, namely, Base power supply (BPS), operates at low frequency and produces majority of the output voltage and power. The other one, namely, fast power supply (FPS), operating at high frequency and low output voltage supplies the remaining power and takes care of the transient variations of line and load and provides the required regulation. The final output voltage is obtained as sum of the outputs of BPS & FPS. Each of the BPS & FPS use phase modulated-series resonant converter as the power-processing unit with zero voltage switching (ZVS). This topology also allows load frequency variation over a certain range.
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