[Amps] Resonant choke filter

[Will Matney]

Peter,
Yes, there's a minimum inductance which can be figured by L = 0.11 x E / 
Imin. Imin can be figured from the bleeder resistor or minimum current 
draw of a device. As long as it is over this value, it will be ok. Keep 
in mind that a choke will not saturate if it's a swinging choke and the 
inductance "swings" with the dc current drawn through it. A swinging 
choke means that the core is gapped and really all are to some extent. 
Even when using interleaved EI cores, they still are considered to have 
a small gap. However, interleaved cores could still saturate in my 
opinion if the demand on them was great enough. Non-interleaved EI or 
gapped C cores are really what you want. Remember also I mentioned 
tuning this choke by fiddling with the capacitance. I've never seen any 
of the chokes right on the money so playing with the capacitance is what 
you would want. It will still be withing the range you calculate.

Will Matney

peter.chadwick at Zarlink.Com wrote:

>
>
>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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