Hi Rick,
I don't know where he gets that the output voltage will be any different with
the choke in the negative lead rather than the positive lead. As far as
rectifying the voltage across the
choke for a bias supply?? That one has me too. It seems it would go all over
the place.
Negative lead filtering works just as well as positive lead filtering. The only
thing you have to be careful of is the transformer center tap. Some
transformers are designed to have the
center tap grounded. They have very little insulation. If the choke was put in
the negative lead with one of those transformers it could arc to ground
internally and destroy the
transformer. That same transformer could not be used with a full wave bridge
either.
The advantage to negative lead filtering is that the choke is not at full DC
voltage. It can have less DC voltage ratting than if it were in the positive
lead.
But for an SSB power supply a choke is not used unless it is a tuned choke. So
negative lead filtering would not exist.
Most of the older ARRL handbooks have a little on negative lead filtering and
so does Orr's handbook.
73
Gary K4FMX
RICK COLE wrote:
> Richard Brummer wrote about NEGATIVE LEAD FILTERING....this is the first time
> i have heard of this thing so where do i go to learn more about it..a net
> search did not help much at all
> Rick
>
> Re:
> "What you have is a transformer which was designed for use with negative
> lead filtering. The peak DC voltage with full wave rectification at no
> load will be about 1814 volts, 2500 / 2 = 1250; 1250 x SQRT(2) = ~1814,
> hence the warning on the transformer."
>
> Yes, and there is much to be said in favor of negative lead filtering.
> (filter choke
> from transformer centertap to ground) There is little dc stress on the
> filter choke,
> and output voltage is a bit higher than with positive lead filtering. Also
> you can
> rectify the ripple voltage across the filter choke to get (-) bias voltage.
>
> Richard Brunner, AA1P
>
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