Naoki Murakami

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.<<ETX>>

Low reverse transfer capacitance VDMOS transistor

A VDMOS (vertical double-diffused metal-oxide semiconductor) transistor structure is proposed that reduces reverse transfer capacitance. The structure features an additional p-region formed at the surface of the n-epitaxial layer, using a poly-Si gate as a mask. Its measured reverse transfer capacitance is about 50% less than that of the conventional VDMOS, and the rise time reduced 50%. measured I/sub D/-V/sub DS/, drain-source breakdown, and switching characteristics are also presented.<<ETX>>

Analysis of high-frequency resistance in transformers

An accurate, analytical method is proposed for calculating the lead and winding high-frequency resistance of complex transformer constructions. High-frequency resistance is derived from the resulting matrix system equations, common to the leads and windings. The effect of eddy currents in the leads is confirmed by theoretical results. The high-frequency resistances of three winding arrangements are compared, and a winding geometry that reduces winding high-frequency resistance is derived.<<ETX>>