[time-nuts] Super Regulator links

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Dec 13 21:47:36 EST 2007

Matt Ettus wrote:
> Can you explain to me the use of fast recovery diodes if you are going
> to put capacitors across them?
Even with the snubber networks the reverse conduction time of the fast
recovery diodes is considerably shorter than when a standard recovery
rectifier is used.
Its the high current pulse during rectifier reverse recovery time that
generates the RFI when standard recovery rectifiers are used.
The transformer leakage inductance also exacerbates the situation
especially if a shunt capacitor and/or snubber isnt placed across the
rectifier AC input close to the rectifier.
As long as the reverse recovery isnt too abrupt fast recovery diodes
generate less RFI (at least at low RF frequencies) than standard
recovery rectifiers even when the input frequency is relatively low
(50Hz, 60Hz etc).

The effect of the additional capacitors and snubbers (particularly the
one across the rectifier AC input) is noticeable even when using
standard recovery diodes.
You can detect the RFI generated by unsnubbed rectifiers with an AM
radio at surprisingly large distances, when properly snubbed you have to
get much closer.
>> You also have to bear in mind the market into which he is selling these
>> devices, they expect some hype of this sort.
> The market he is selling into expects snake oil.
Thats why you have to make allowances.
> Matt

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