Some real brain fodder here. John P. Your Spice model with the coupled
inductors seems to take a divergent turn and I am not sure about this
"coupled" part. Did you try a single inductor.

On to my original thoughts. This really takes me back and requires serious
thought. One thing to keep in mind. An inductor (by virtue of the
magnetic field cutting its own turns) tries to keep whatever current is
flowing, flowing. An inductor will make the voltage across it "do whatever
it takes" to keep that current flowing-- and allow this current to decay
(some say discharge) in what can be considered a normal manner. The diode
on the relay coil is a good example. The voltage can rise very high without
the diode, but using this model, you can figure out what the inductor
voltage does when the normally conducting device turns off.

That said... I had never studied choke input filters to such a degree...
However, its action must allow the filter cap to charge for a longer time,
thus keeping the average diode current lower...
Does the current through the inductor drop to zero in the normal choke input
filter?
If not, a close look at the current path in the full-wave circuit will show
where the current goes at the cross-over points. Brain full - can't figure
out now. I'd have to model it in Spice and watch things

Very interesting thingh. If the current does drop to zero, then it seems
the single choke would work.

Then, reading some of the latter posts, I too, wonder why the desire for
choke input.

73, Steve, K,9;D.C'I



John Popelish" wrote in message
...
Fred McKenzie wrote:
In article , Ken Scharf
wrote:


I was looking at some power supply circuits for
tube linears and was thinking about the full wave
voltage doubler. This is basicly two half wave
rectifiers in series. Now I could build this
circuit with a choke input filter for each half
wave rectifier of the voltage doubler, and I could
put the chokes in the lead without the rectifier.
In this case I could use one choke for both halfs
of the voltage doubler.


Ken-

This doesn't make sense to me. My recollection of the choke-input
filter,
is that it can only be used following a full-wave rectifier. You are
suggesting they be used prior to the rectifier, which is not where a
"filter" is normally placed. Instead, the choke would act as a series
impedance to the AC source.

It seems to me that you can't separate the capacitors from the
rectifiers,
or you wouldn't have doubler action. Therefore, capacitor-input is the
only filtering that makes sense for this circuit. Of course you might
use
the choke in a Pi configuration between the output and another filter
capacitor.

If you have any success with this approach, it will be from extra
voltage
generated by the choke's collapsing magnetic field. This is similar to
how switching regulators work, but without any active regulation.

73, Fred, K4DII

I played around with choke input filtering for this circuit with Spice
and got "continuous inductor current" if I used two highly coupled
inductors, one after each rectifier, and another pair of diodes from
the input side of the chokes to the capacitor common point. However,
this "continuous current" switches back and forth between the two
coupled inductors on alternating half cycles so each end of the
capacitor pair sees current as a half cycle approximately square wave
pulse. So each capacitor charges and discharges with a quite
triangular voltage ripple. But the sum of the two capacitor voltages
is a very pure DC, compared to the no choke version, since the ripples
cancel quite well. However, this reduces the output voltage to only
half of the no choke version, so you might as well have made a full
wave supply, instead of a doubler configuration.