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Reduction of harmonic energy.

Posted by Al Sekela (A) on November 1, 2009 at 12:06:42

In Reply to: Fast, soft recovery diodes posted by megalomaniac on November 1, 2009 at 10:24:38:

Junction diodes store electric charge during forward conduction, and this charge is removed in the form of a pulse of reverse current upon reversal of the applied voltage. There are two consequences in mainstream electronic applications (not audio equipment power supplies): the pulse represents an energy loss mechanism in switching power supplies, and the shape of the pulse translates into an RF energy spectrum in applications where RF noise is a concern.

The steeper the trailing edge of the pulse, the more high harmonic content it has, due to Fourier's theorem. Thus, diode designs that minimize total charge in the pulse at the expense of a steep trailing edge will have lower energy loss but generate more RF noise. Designs that tailor the trailing edge to reduce RF noise may waste more energy in switching power supplies.

For audio use, both are still important. The pulses from diodes used as rectifiers stimulate associated power supply parts to ring. The charge magnitude may generate ringing even if the trailing edge is considered 'soft' for other applications. I think one would have to experiment with different available diodes to see which gives the most quiet results.

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