In high voltage input DC-DC converter, auxiliary winding of isolation transformer\nis usually used to supply power for control circuit. Due to the widerange\nof input voltage, the variable output voltage of auxiliary winding will\ncause a series of problems, such as variable drive pulse amplitude, increased\ndriver switching devices loss and drive transformer core saturation. This paper\nanalyzes the influence of variable output voltage of auxiliary winding in\ndetail. A novel method is proposed to solve the problem of large variation\nrange of auxiliary winding output voltage, which is adding a buck converter\nbetween the auxiliary winding and the control circuit. A dual switch forward\nconvert has been designed with 300 V - 800 V input and 24 V/5 A output. The\nresults show that this method is effective by comparing the different results of\nusing buck converter or not.
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