For a filter inductor in an LC filter, does the inductor size (core volume) scale linearly with inductance * current rating^2, all other variables the same, ie. core material, frequency etc.
Also I need some toroid cores for 200kHz LC filters, 250uH and 50Amps peak current, are these going to be huge cores and what core materials would be best to use, ferrite or powder cores?
I've downloaded the
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"Magnetics Inductor Design Using Powder Cores" program:
That's stored energy, which should be proportional to core volume.
Iron powder cores tend to burn their paint off in situations like this. Permalloy powder is very good but expensive. The "Kool-Mu" cores are almost as good, but cheaper. Gapped ferrites are OK here, too.
And... ur decreases especially on the knee to saturation.
Like biasing a transistor, best not to over bias. There has to be useful permeability for your target inductance. I've seen some app sheets suggest operating a ferrite toroid at
To properly design that inductor more info is needed, such as; Iac (For core, proximity and skin effect losses), Idc (For I^2R losses), Ipk (for core max flux density) and E*T (core saturation) along with the operating frequency already given. Max ambient temp, inductor temp rise and size constrains would be helpful. Given that we can then offer an opinion. Cheers, Harry
:-) My question here would be something along the lines of "why on earth do you need 250uH at 200kHz and 50 amps??" To me it implies either a huge amount of power (i^2*L*f/2; at rather high voltage), or a poorly/strangely designed filter system. If it's lots of power, you should of course expect to be using relatively large parts, and it's worth thinking very carefully about the design of the inductor and the system into which it fits--probably not something to just jump into without experience at lower power first. -- I wonder what it is that Jamie is actually trying to accomplish.
I have a simulator of the PWM controller for this circuit, if I set it to output 3.6kW at 120VAC, with a 250uH inductor and 10uF cap I get this waveform: (THD + noise = 1.7%)
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With an inductor RMS current of 28.5amps and peak current of 45Amps and capacitor RMS current of 1.8Amps and peak of 5.2Amps.
If I change the inductor to 50uH and the cap to 100uF, I get this waveform: (THD + noise = 2.4%)
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With an inductor RMS current of 32amps and peak current of 86Amps and capacitor RMS current of 17Amps and peak of 46Amps.
This larger 100uF cap is required with the smaller inductor or else there is way too much ripple. Also this 100uF cap will be expensive as it has a large current rating requirement.
It seems like a tradeoff, if going for the 250uH/45Amp inductor, what toroid material would be good and still economical to use?
I am planning on ordering some various toroids so I can experiment with winding them and stacking them if necessary, so am looking for the best core types to be using for this.
I saw Beowulf last night..cool graphics, Jolie is hot but I did wayyy too much fast forwarding.
Here's my version of Beowulf :)
King makes noisy party. Next door neighbor Grendal gets pissed, shows up, eats people. Grendal doesn't eat the King even when taunted. Mystery. Hired gun Beowulf shows up. Beowulf gets to boink the kings wife if he kills Grendal. Beowulf kills Grendal. Beowulf boinks kings wife. Grendal's mom gets pissed, shows up, kills people. Beowulf visits Grendal's mom.. What a hot milf! The deal. Beowulf boinks Grendal's mom and her magic makes Beowulf 'Super King'. (Grendal's mom likes popping out human/monster hybrid kids.) All's well until some jerk steals the horn from Grendal's mom. Her new son goes postal. Beowulf kills that one too. Beowulf dies. Successor to the throne wants some xxx with Grendal's mom. What a hot milf! And the cycle continues..
Jamie, Your Vout + PWM waveforms confuse me. The frequency of the output and PWM is about 0.35Hz. There is no PWM just a square wave and the filtered output is shifted 0 or 360d and at that amplitude and phase cannot be the filtered output. Please advise, Harry
?? Seems to me a reasonable starting point would be about 5uH and
10uF (comprising perhaps ten 1.0uF or twenty 0.47uF high quality polypropylene caps) as a first stage out of the FET bridge, followed by perhaps 1uH and another 10uF (which doesn't have nearly as high a ripple current), to yield a fraction of a volt p-p 200kHz ripple at the output, assuming a 3 ohm load and 150V out, input switching to
+200 for 4.3us and -200 for balance of the 5usec cycle. Looks like it does OK through the range of duty cycles needed to generate the output
60Hz sinewave. Though the first-stage capacitor has to handle a lot of ripple current, I'll bet you'll find that doing it this way, with a couple stages, will be cheaper by far than a 250uH inductor that meets your needs. I believe Wima MKP10 caps would do OK in this application. If you have frequencies lower than 200kHz on the output, I'd recommend solving that with a better control system.
Perhaps I don't understand just what you are doing, but at least the way that's obvious to me to generate a "clean" 60Hz wave from the partial schematic you provided suggests to me that you don't need anywhere near 250uH to do what you want.
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