Re: conventional power supply

Ban wrote...

During the simulations I tried various caps and snubbers across
the rectifier diodes and found another audiophool myth. These
caps indeed reduce the even harmonics in the diode current,
but... the odd ones which are 30dB higher stay identical. So
what is the use?

That's not what they are for. Your entire analysis has a huge
error, in that you ignore the transformer's leakage inductance.
As I showed in multiple postings of measurements on ac-line
transformers, voltage drops from leakage inductance typically
exceed those from copper resistance. The s.e.d. threads also
have extensive theory and formulas to calculate transformer
leakage inductance, and these reinforced my observations.

While the inductance does not contribute to power dissipation,
it has a *huge* effect on your rectifier and filter-capacitor
calculations. This is good, because it serves to reduce the
inrush current at the top of each half-cycle, spreading it out.

A complete and accurate analysis will have to include not only
the transformer's leakage inductance but the diode's reverse-
recovery time model. You have some more learning ahead of you.

Back to your snubber, this is to damp the inductive pulse and
high-frequency ringing that occurs from the rectifier diode's
fast snap-off after the reverse-recovery time is finished. In
this case it's the transformer's leakage inductance that was
charged during the reverse-recovery time and forms a resonant
circuit with the winding and diode capacitances. You add more
capacitance in parallel to lower the ringing frequency and take
control of the resonant energy, plus a series resistor to lower
the Q and damp the ringing to a single cycle. (We've written
up a nice story about this scene, complete with scope photos
and spice models for the 3rd edition of AoE.)

Anyway, instead of a very sharp high-voltage spike (too short
to see with a scope unless you trigger properly) followed by
RF ringing, you get a single small long smeared-out innocuous
pulse. If left unattended to, the magnetic radiation from the
inductive spikes can be picked up and create an audible buzzing
signal (harmonics of 120Hz) in low-level phono or mic inputs.


--
Thanks,
- Win
.

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