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In Reply to: Take a look at I(T1) posted by Russ57 on May 9, 2007 at 05:09:18:
Hey Russ,I'm not sure that it matters either, but it sure is fun to look at. ;-)
When all of the talk of RF hash being created and broadcast, i thought it might be interesting to look for the source. This is when i noticed that the current waveform for the "real choke input" seemed to have the most HF content.
How this content gets out is a whole new can of worms i'll save for a later discussion. What i do want to point out is that a distorted current drawn through a resistance gives a distorted voltage. luckily we can consider the line voltage to be a very low impedance source so this would seem to minimize the damage, but remember we do need to add the DCR of the windings as series resistors and suddenly we have the mechanism in place for the creation of a distorted voltage.
still not sure what that means in sonic reality, but we are determining merit by simulation dammit and i say the prettiest picture must sound best.
I'll also add that it seems logical that both undistorted current and voltage waveforms are desired when dealing with filter systems.
Follow Ups:
"This is when i noticed that the current waveform for the "real choke input" seemed to have the most HF content."I don't understand. Are you saying that this will throw more RF than the one in the link below?
There are two "spikes" per cycle in both waveforms and these are much smaller than the spikes without the choke.
Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
In this scale, RF content is represented by a vertical line. the more the line approaches a pure vertical, the higher the frequency content. The magnitude of the signals has nothing to do with this. By adding a small choke in front of the first C you end up greatly reducing the narrowness of the current draw "spike" netting what appears to me to be a current draw with much less high frequency content than even a "real" choke input filter.
"By adding a small choke in front of the first C you end up greatly reducing the narrowness of the current draw "spike" netting what appears to me to be a current draw with much less high frequency content than even a "real" choke input filter."In this example, what value choke would be "best".
Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The best choke would be the one chosen by ear, but since we are in sim land you first have to decide what you want the current to look like then decide what looks best. How that translates to what sounds best is still up for discussion.
Anything that adds resistance/impedance between wall power and first cap will help increase conduction angle. Any increase in conduction angle moves you closer to a real choke input supply.Play around....up the transformer DCR...go to FWCT and a 5U4....try an RC filter stage. There is no best here. It is more of a mental exercise and to see if what looks "pretty" on the scope/sim.....and/or.....to see/hear if drawing current at a steady constant level (that reverses each 1/2 cycle) is better than drawing current in sine wave manner. Don't forget to increase load as needed.
Being who and what we are here, I reckon when we see an evil square wave we freak and think "sum of odd order harmonics".
but russ, that Evil R instantly converts distorted current into distorted voltage.
I didn't mean best in that way. When I add a small choke it lowers the amplitude but doesn't change the shape. Am I missing something?Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
if it lowers the amplitude, it has to change the shape. Assuming the same power into the load, the area under the plots must remain the same independent of filter type, so if you decrease amplitude, you must widen the trace at some point to keep the area constant.
It appears that the total magnitude is higher for green, but green drops off faster/more with increasing frequency. I'm a little hesitant to mindlessly trust the sim results. It would be interesting to build just these two simple supplies and measure the actual noise.
Yes, the FFT plot was an eye opener. I'll take it as gospel but it wasn't what I expected!So if we are going to draw power from a transformer and feed it into reactive parts how do we get some same voltage and current waveforms that we would if said transformer supplied power to a resistive load? I suggested one way but perhaps you have another you'd like to share? Also, have you played around with putting line reactors (chokes) before the power transformer? Maybe if we "contained" all the bad looking stuff to only the PT we are doing fine???
Anyhow, interesting discussion and I am glad to see I am not totally off base.
Russ
P.S. It looked like you were a little "kind" with the cap input filter. Perhaps we could come up with one that had worse spikes and see how that models.
actually the green trace was for a Low L input filter... it sort of takes the edge of the full C input.
Did the choke and cap models include parasitics? I've been playing around quite a bit with Spice sims of supplies and the effects are an eye opener above the first cap self-resonance.
Thermionically addicted.
Even on a picture-only basis, we're looking at less than half. Step Tre's 250H/220uF load and see what happens to the current.
Thermionically addicted.
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