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In Reply to: RE: 4 pole caps in a voltage doubler circuit posted by Eli Duttman on July 29, 2012 at 18:55:00
Choke and cap in parallel?
Inserted in series from the voltage doubler stack to the B+ power supply filters?
A choke and cap in parallel form a tuned circuit, which, if reasonably high in Q and in series with the rectified B+, will only be effective (as a filter) around the resonant frequency. I blieve what you want is a simple choke, which will have increased impedance as the frequency is increased.
No - the small choke goes in series between the doubler stack and the filter caps, the 1000pf goes to ground downstream of the choke and ahead of the filter caps. It's a simple LC filter.
Edited to make small clarification...
Treat the disease and not the symptom - use ultrafast soft recovery diodes for the restifier. They will produce 5 times less "hash" than standard diodes.
Even when zero switching noise Schottky diodes are employed, an issue remains to be dealt with, if high value caps. are installed in the doubler stack. Large amounts of capacitance imply a tiny conduction angle and a highly "triangular" ripple waveform. Per Fourier's Theorem, such a waveform contains high order harmonics of the ripple fundamental that extend well up into RF. The winding capacitance of a commonplace PSU filter choke is a short circuit at RF. The "hash" filter eliminates the crud that would sneak past the "routine" filter choke.
BTW, the "hash" filter also disposes of garbage riding on the AC mains.
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