On 01-01-98 Alec Cameron wrote to Day Brown... 
 AC> Warning- tho the iron leaves will sop up the magnetically coupled 
 AC> spikes, 
 AC> there is a second route to worry about- the capacitance distributed 
 AC> along the 
 AC> windings. For steep spikes and high frequency AC, this capacitance 
 AC> "conducts" 
 AC> the spike really well. That's why transformers sometimes have an 
 AC> earthed 
 AC> shield between primary and secondary windings- to suppress the spike 
 AC> or "noise" so it doesn't travel via capacitance. 
Agreed.  I think the point was mentioned in the German PFC study, 
and that the capacitive spikes were picked up by the PWM chip, as 
well as, or instead of, the slope of the AC wave it was designed 
to be monitoring. 
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