Rich,
I'm running a regulator after the swinging choke for the bench supply. I
was wanting to do this to try and clean up the ripple before the
regulator had to handle it (plus I have a surplus swinging choke). If I
hadn't wanted the regulator, I would have tried a straight resonant
choke. I would think that the regulator would hold the choke output
current some steadier unless I'm not thinking correctly. Also, by what
I've read, the chokes made today using interleaved lams still act
somewhat like a resonant choke with a gap but the swing is not as large.
I seen a couple of remarks that they could not saturate easily, but I
think they can. You are correct though that without a constant load, the
circuit can produce transients and spikes especially if the bleeder
resistor opens or is not sized correctly. The circuit I'm using is a
standard choke input with capacitance across the choke to resonate at
120Hz. There is no capacitor to ground before the choke (capacitive
input) which is very bad to produce high voltage spikes. Let me know if
you have any ideas on this before I fire up my iron =)
Will
R. Measures wrote:
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@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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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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