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Old November 20th 05, 04:16 PM posted to rec.radio.amateur.homebrew
Fred McKenzie
 
Posts: n/a
Default choke input voltage doubler?

In article , "wa2mze(spamless)"
wrote:

I think I understand what you are saying here, but even with
a full wave rectifier doesn't the current through the choke drop
to zero (though only for a brief instant) between the two phases
of rectification when the diodes switch roles? And since there
isn't a capacitor before the chokes the voltage at the input
to the filter would drop to zero, unlike with a capacitor input
filter.

Also, with either type of rectifier (FW or HW) is shouldn't matter
which leg the choke is placed in, as Kirkoff's law is satified
either way.


Spamless-

Yes, it wouldn't matter what leg the choke is in as long as it is on the
output side of the rectifier (assuming full wave).

For Half Wave, you must also consider the voltage across the choke.
Voltage is L times di/dt where di/dt is very high at the moment the diode
stops conducting. This is why a diode is often placed across a solenoid
or relay coil, to prevent a high voltage pulse across the switching
device. As a side-effect, relay drop-out is slow since current continues
flowing as the magnetic field is discharged.

With the relay analogy in mind, perhaps there could be some advantage if a
diode were placed across the choke of a choke input filter fed with a half
wave rectifier. It would be connected with cathode towards the cathode
end of the rectifier, and would allow choke current to continue flowing
during the off-portion of the rectifier's conduction cycle.

73, Fred, K4DII