Is actual resonance what you want? The argument I've seen runs as follows;
In a choke input supply, there's a critical minimum value of inductance for
regulation. At low currents, this is very high, but if the choke is tuned
slightly HF of the ripple frequency, it looks like a very much bigger
inductance. At resonance, it will look like a resistor, of course. As the
load current increases, the critical value of inductance decreases, and the
choke will start to lose inductance anyway.
From this, the choke needs to be tuned a tad HF at minimum load. This
certainly ahs worked for me. Incidentally, by using negative lead
filtering, you can rectify the ripple across the choke for a low current
negative bias supply.....
I tend to go for negative lead filtering anyway to ease the choke
insulation requirements.
73
Peter G3RZP
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