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Re: [Amps] Power transformer for 600 watt rig

Subject: Re: [Amps] Power transformer for 600 watt rig
Date: Tue, 18 Mar 2008 19:11:16 -0700
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I can't comments on the swinging choke, I haven't looked at that.  However, 
I've done quite a bit of modeling of a design I'm planning and find that a 
tuned choke does not solve the dynamic regulation problems of a regular choke.

The tuned choke provides a high impedance at the fundamental ripple frequency 
and therefore tends to produce an averaging effect on the output voltage with 
a minimum load on the supply.  I.e., it does keep the output voltage 
from "soaring" if the critical inductance value is not otherwise met for the 
minimum load condition.

However, adding a small value capacitor in parallel with the choke does not 
solve the problem that when the load suddenly increases (or decreases) the 
current through the choke [actually the choke and resonating capacitor in 
parallel] does not change rapidly enough to avoid an undershoot (or 
overshoot) in the output voltage of the supply.  With abrupt load changes, 
there is also the expected ringing on the output at about the resonant 
frequency of the choke and filter capacitor.

The dynamic regulation problem can be minimized by using a smaller value of L 
and larger value of C.  With a tuned choke, the minimum load can still be 
reasonable.  A lot of the other benefits of a choke-input filter (i.e., lower 
transformer dissipation, lower AC line peak currents, voltage drops, and 
losses, more favorable rectifier operating conditions, etc.) can still be 
attained for high output currents where they matter most.

Warren, NR0V


To: "'jeremy-ca'" <>, "'Amps'" 
Sent: Tue, 18 Mar 2008 20:21:29 -0400
Subject: Re: [Amps] Power transformer for 600 watt rig

Filtering isn't the problem. Dynamic regulation is a problem with a choke.
You get severe voltage drops when current is drawn at an audio rate from the
power supply. A swinging choke is even worse than a regular choke. They
should never be used in an SSB power supply.
Put a scope on the high voltage output of the supply with a choke (thru
appropriate divider resistors) and you will see some pretty nasty looking
voltage drops with modulation.
Only a tuned choke is desirable as it does not have the problems of a
regular choke.

Series resistance of the transformer is the second problem for voltage
regulation in a power supply used for SSB. We want as low a resistance as we
can get. Most of the older power transformers are not well suited for SSB
operation because of their rather high series resistance.

Gary  K4FMX

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