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.