question about dc filter choke in power supply

Lane Zeitler zeitler at IBM.NET
Sat Aug 7 20:54:10 EDT 1999

The next project is a dc power supply that will go as high as 4500 vdc at 1
amp CCS. I will be using a new Dahl xmfr and a dc resonant filter choke
followed by a cap. This is going to be the universal power supply for
numerous amp projects.

Scenario: Output E of one of the taps is 2400 vac. Using a full wave bridge
followed by a resonant choke I get 2150 vdc at the output; approx. 90%. This
is where it should be using ony a choke.

Now follow the choke by a cap. In this case 15uF at 5 kv (just happened to
be in the junk box). Now the output voltage is 2480 vdc.

The "output factor" went from .9 to 1.05.

Why the increse in output voltage when the cap is in place?

90% of xmfr secondary voltage with just choke and 105% with the choke
followed by the cap.

I am sure the answer is very basic but for some reason I lost the concept.


Lane Zeitler
San Diego

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