Noise reduction mechanism in common-source type active-clamped DC-DC converters

We have pointed out that the common-source type active-clamp converter has a good feature of common-mode noise reduction and have shown its low noise characteristics. This paper analyzes the noise reduction mechanism in the common-source type active-clamp converter in detail. By measuring the near-field magnetic radiated noise, we examine the noise current path on the converter circuit board at some frequencies in problem. From this analysis we derive a high-frequency equivalent circuit for conducted noise current. The effect of stray capacitances on the near-field magnetic radiated noise frequencies is examined to confirm the validity of the high-frequency equivalent circuit. It is shown that the near-field magnetic radiated noise is reduced by shrinking the noise current loop.