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Old 15th January 2013, 11:30 AM   #101
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Just think about it: In a well-balanced PP output stage the same amount of idle current, and thus the same amount of ripple current, flows through each primarie's half, but in opposite directions, thus balancing the magnetic fluxes induced by both.

The ohmic resistance, as only this would dissipate heat, doesn't matter at all in this context!

Best regards!
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Old 16th January 2013, 12:39 AM   #102
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uh, half the transformer primary is trying to make magnetic flux one way, and the other half of the transformer primary is trying to make magnetic flux the other way, I'd expact that to mostly turn all that opposed energy into heat and output nothing at all.
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Old 21st January 2013, 05:51 AM   #103
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I've been looking for a Thermistor (or perhaps more than one) to limit the in-rush current as the big filter caps fill. Like these:
http://www.partsconnexion.com/prod_pdf/thermo_74671.pdf
from this vendor:
Parts ConneXion - The authority on hi-fi DIY parts and components
This is just a soft-start to protect the transformer at start-up, as I intend to use a very hefty bridge that should handle any turn-on in-rush to the first cap. It might be good for the cap's lifespan too. I'm really hoping the thermistor is not ever needed during operation; I'd rather blow a fuse than limit performance, as I'm not looking for sag. The thermistor is probably not needed at all, but I'll need to run another simulation. When the first filter caps start to fill, the transformer always sees a ridiculously low impedance, my concern is how long it sees that load, which will be clear in simulation. If you can offer relevant advice, I'd appreciate it. If it makes the first main cap fill more slowly, it will also prevent the big coil from ringing and momentarily overshooting the rail voltage, which could be bad for subsequent components. A slow-blow fuse should be in here somewhere too.
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Old 21st January 2013, 06:01 AM   #104
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After a big main cap and the big choke, a capacitance-multiplier circuit does sound like a perfectly suited and compact way to practically eliminate residual ripple. So how does that behave at start-up and how do I simulate it?
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Old 21st January 2013, 08:29 AM   #105
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I have been looking at the ByBee Music Rail DC power conditioner, with the additional zeners and caps for high-voltage B+ applications. I'm assuming it's mostly a capacitance mutiplier. In fact, it sounds nearly perfectly suited for after the first big main cap and choke form a huge supply. I don't need a huge current reserve there, just something to get rid of a bit of residual ripple.

http://www.partsconnexion.com/bybee_musical_rails.html
http://bybeelabs.com/Apps___Data.html
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Old 28th January 2013, 05:39 PM   #106
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Now I'm looking for that capacitance-mulitplier circuit someone posted to this earlier.
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Old 28th January 2013, 06:10 PM   #107
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I decided I'm probably not going to use that enormous choke. It's just TOO heavy and difficult to package. Very difficult to find the perfect choke unless I have it made. Instead I've been considering weird things like two smaller chokes and a resistor in parallel. Very hard to model. Might really work well though, and ring less, and still have less voltage drop than just a resistor. The regualtion might be a bit less stiff than the enormous choke, but the ripple looks OK. Also some basic decisions to make, like under extreme load is it worse to sag or to ripple? I'd think the 60Hz would be mostly masked by loud signal, but I don't want hum trailing dynamics either. I think it's workable with a big cap or capacitance multiplier.
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Old 29th January 2013, 04:49 PM   #108
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Looks like a low-Q choke or a resistor in parallel with a choke rings less and carries more current, but gives worse isolation between filter stages unless the choke has more inductance. The ideal way to damp seems to be a big cap in series with a resistor (both in parallel with the final cap), but that damping cap is supposed to be 16 times the capacitance of the final filter cap. Perhaps that damping cap is a really ideal place for a capactitance multiplier, absorbing ringing more than ripple. Now where was that post someone made with a circuit for a capacitance multiplier using an FET?
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Old 29th January 2013, 06:53 PM   #109
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A resistor in parallel to your choke is not the best idea. It more or less cancels out the benefits from the inductance. Finally, I don't understand what you mean with 'ringing'?

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Old 30th January 2013, 06:31 PM   #110
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Check this out:
http://www.designers-guide.org/Design/bypassing.pdf
I'm proposing a little of figure 8 "B" on each inductor, and a little of figure 9 after it all. Of course, it's easy to make things worse instead of better.

For instance (worst case ringing), if all the components are very good (inductor has good Q, caps have low ESR) and imagine I have 1000uF across the rails, then 1.5 F inductor in the hot rail, then another 1000uF across the rails, whenever there's a change in load there's a current surge that "bouces" thru the inductor from one cap to the other and back and forth. It doesn't show up in steady-state simulation, but occurs when something changes, like the load. For this kind of application you really
want an inductor with a rather low Q that's not tuned sdso sharp when it all gets in resonance. A resistor in parallel with the choke does indeed harm the isolation the choke provides between the rungs of the filter ladder. And the inductor was more efficient than an inductor but the resistor loses some of that advantage. And the resistor probably hurts the inductor's superior high-frequency performance, but I'd hope the final cap fixes that. One preferred solution, instead of making the choke "worse" is to de-tune or damp some other way like a resistor in series with the last cap, tuned so it damps the oscillation by burning some off; unfortunately that resistor is like ESR and will ruin the cap's high-frequency performance for smoothing the edges of the ripple in fixing this low-requency ringing. So it requires another capacitor without a resistor in parallel with the one with the resistor. Unforutnately, in order to damp the ringing optimally, the capacitor with the resistor should be about 16 times the size of the one without.

Yes, damping the ringing makes the inductor and cap work worse. Just like a simple friction damper on an old auto suspension makes the suspendion less compiant Maybe there's an easier way involving diodes, or would that drop voltage?

Maybe there's an easier way of using a gyrator circuit to emulate a large inductor?

A capacitance multiplier is really nice for hadling the ripple, but I'm not so sure it's cut out for damping this ringing.
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