Combined Two-Transistor Forward Converter with Output Coupled-Inductor and High Voltage Gain

To overcome drawbacks of the low duty cycle and the low voltage gain of two-transistor forward converter(TTFC) and only in low output voltage,a novel combined two-transistor forward converter(CTTFC) with a output filter coupled-inductor is proposed.The converter is connected in parallel on the input side for the higher input current and in series by the coupled-inductor on the output side for the higher output voltage.The CTTFC has high reliability and the valid duty cycle.Its voltage gain is four times than that of the TTFC.So under the condition of the same input and output voltages,the voltage stress of secondary side freewheeling diodes of CTTFC is 1/4 of the corresponding diodes of the TTFC.As a result,the CTTFC is suited to the high output voltage application,and its secondary side freewheeling diodes can be replaced by low voltage fast recovery ones,thus improving the reverse-recovery problem of diodes and enhancing the reliability of the converter.