[Amps] Resonant choke filter

[R.Measures]

On Aug 2, 2004, at 10:54 AM, Will Matney wrote:

> Peter,
> With looking through the books texts I have here, That is the way you 
> design this filter using a swinging choke. With mine, I needed 400 Vdc 
> @ 80mA maximum. So Lcrit = E / Imax which is 400 / 80 = 5 Henrys. Now 
> the choke is a 5-20 henry swinging choke. So to get the minimum 
> current for the bleeder resistor to have the 20 Henry portion we take 
> 400 / 20mA = 20 Henrys or 20H x 20mA = 400V. So for 20 mA at 500 
> Volts, our bleeder resistor would be 400 / .02 = 20K ohms. Then to 
> size the wattage, 400 x .02 = 8 watts. A 10 or 15 watt resistor would 
> work here. As long as Lcrit is met, the swinging chokes inductance 
> will swing and level out with the DC load without saturating.

Will --  Swinging filter chokes work well with constant current loads 
such as RTTY, FM, and AM linear amplifier service.  However, with a 
varying current load, such as in a SSB linear amplifier, they do not 
provide satisfactory transient regulation.  The only types of filter 
that do are the capacitor-type and the resonant-choke-type.  Those who 
doubt this should do a bench test with a DC oscilloscope since a meter 
can not follow the transients.  Step up or down the load current and 
the resultant V-transients are no less than amazing.  This is the 
reason why Harris, Collins, Henry, Hughes, and other manufacturers of 
SSB amplifiers use resonant-choke filters.
end

> If Lcrit is below this value, it will try to run as a capacitive input 
> filter. Actually, I will be adding a page on filters to the 
> transformer tutorial when I get to feeling like it as promised. I have 
> some done, but nothing ready yet to publish it. Last, Tony, I0JX, has 
> a page on this at:  http://www.qsl.net/i0jx/supply.html
>
> 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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>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org