| 270V DC power system is an attractive alternative aviation primary power system. The equipments for communication, control and protection in aircraft need the power supplies with low DC voltage of 3.3V, 5V and±12V, so a multi-output converter is required to convert the high voltage of 270V to these low voltages.The multi-output converter should have good output voltage cross regulation, high efficiency, small size, etc. In order to meet such requirements, this thesis proposes a two-stage approach for the multi-output converter. The first stage is a half-bridge converter, which is operated at full duty cycle, i.e., the duty cycle of each switch is 0.5. The output rectifiers for +12V and ?12V are Schottky diode rectifiers for simplifying the circuit, and the output rectifiers for 3.3V and 5V are synchronous rectifiers to reduce the conduction loss. The second stage is synchronous Buck converter, each of them are independently controlled to obtain a well-regulated output voltage.The parameters design of the power stage of the converter is discussed in this thesis as well as the devices and components selection. And the transformer design and its PCB windings arrangement are analyzed. The small signal models of half-bridge converter and Buck converter are derived, and based on which, the output impendence of the half-bridge converter and the input impedance of the Buck converter is calculated. It is found that the magnitude of the output impendence of the first stage is smaller than the input impendence of the second stage over the whole frequency range, which means that the two-stage converter is stable.A prototype with 270V input, four outputs including 12V/2A,–12V/1A, 5V/10A and 3.3V/6A is fabricated and tested in the lab, and the experimental results verified that the proposed two-stage approach and the parameter design are effective, and the prototype presents good output voltage cross regulation, high efficiency, fast dynamic respond, and small size.
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