Analysis of a resonant reset condition for a single-ended forward converter

The reset condition of a transformer core flux is analyzed for a single-ended forward converter operating in a resonant reset mode. Relationships between reset time and device parameters such as the main switch output capacitance are derived. As a result, the maximum frequency in a resonant reset mode can be predicted. The main results are: the resonance period of the main transformer flyback voltage is mainly determined by transformer magnetizing inductance, main switch output capacitance, and diode junction capacitance; the main transformer flux excursion is between the first and third quadrant in B-H characteristics; and the maximum operating frequency in the resonant reset mode is determined by the above parameters and volt-second products during main switch on-time. The validity of the analysis is confirmed by comparison with experimental results for a low-power DC-to-DC converter with a 50 V input and a 5 V, 2 A maximum output.<>