DC-DC Converter Inductors work well
not as a blanket statement, but if properly selected.
I found the coilcraft DO3340 to be very linear, but they are not high enough power for what you ask. These are not shielded, which helps with their linearity, but they can crosstalk between adjacent channels
If using a DC-DC inductor, its best to have a good margin of current. Make sure the graph of inductance as a function of current is flat across the range you wish to use it.
not as a blanket statement, but if properly selected.
I found the coilcraft DO3340 to be very linear, but they are not high enough power for what you ask. These are not shielded, which helps with their linearity, but they can crosstalk between adjacent channels
If using a DC-DC inductor, its best to have a good margin of current. Make sure the graph of inductance as a function of current is flat across the range you wish to use it.
Thanks for the reply. Right now I am looking at the JW Miller / Bourns 2300LL (low loss) series. They are rated to 20A for 10uH and slightly less current for 15 or 22uH.
http://www.bourns.com/data/global/pdfs/2300ll_series.pdf
I found searching on this forum that someone used the smaller 2200LL series with success on a Tripath amplifier. What do you think of the 2300LL? I may try to order some and put them on the TAS5518/TAS5261 stereo eval board I have here.
http://www.bourns.com/data/global/pdfs/2300ll_series.pdf
I found searching on this forum that someone used the smaller 2200LL series with success on a Tripath amplifier. What do you think of the 2300LL? I may try to order some and put them on the TAS5518/TAS5261 stereo eval board I have here.
It's not that hard to design and build your own custom inductors. Suitable cores are available at several online shops.
http://www.diyaudio.com/forums/showthread.php?postid=1393703#post1393703
http://www.diyaudio.com/forums/showthread.php?postid=1393703#post1393703
Wurth electronics do some great pre made inductors for class D; like the 10u 20A inductor 7447180 data : http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6171300
low cost and they do a range of values suited to 2,4 and 8 ohm loads- the ferrite bar appears to soft saturate, however carefull design and layout is required as they bleed like pigs!
regards
low cost and they do a range of values suited to 2,4 and 8 ohm loads- the ferrite bar appears to soft saturate, however carefull design and layout is required as they bleed like pigs!
regards
classdphile said:
I am becoming increasingly annoyed by your critisism allied to your lack of contribution; these parts are designed for output filters and soft saturate- which is good; the fact they are a ferrite bar requires carefull layout and mechanical design, of interest to the many here who have hobby and commercial reasons to share their common experiences.
I do not know you or your background, I can only read your posts, English may not be your first language, however you are one of the most negative people I have come across, the replies you make do not contribute, rather deride or enflame, and as the old phrase goes if you have nothing to contribute please don't comment (highly edited to prevent offence)
I am a hobbist and a professional designer, my products are independantly tested and carry certificates to prove this, others on this forum also are involved in the professional allied arts, so we are all in this together.
I like this forum as a repository of knowledge, sharing and understanding, and feel loathed when it contains put downs and bad feelings, I appeal to you to consider others before you post, or find some other medium to vent your feelings.
You're either a hobbyist or you're a professional, not both. Each posts from a certain perspective and for different reasons. As you so often include your credentials, though english may not be my first language there's no doubt as to which you choose to portray.
Invoking hurt feelings when there was nothing personal there, to outright ad hominem such as this, are just fallacies that detract from your professionalism or the sageness that goes with it.
As a professional that wishes to be taken at a higher level as you clearly do per your chorous of credentials, you could better appreciate the scrutiny that can go along with it rather than supposing yourself above it and still expecting to reap whatever benefits. I still await your correction on the NTC soft start for class d. I felt that friendly tip would have gotten you thinking about it, but evidently you can't be wrong.
Rod cores have their uses, this isn't it. I hope this doesn't otherwise take away from our friendship.
Invoking hurt feelings when there was nothing personal there, to outright ad hominem such as this, are just fallacies that detract from your professionalism or the sageness that goes with it.
As a professional that wishes to be taken at a higher level as you clearly do per your chorous of credentials, you could better appreciate the scrutiny that can go along with it rather than supposing yourself above it and still expecting to reap whatever benefits. I still await your correction on the NTC soft start for class d. I felt that friendly tip would have gotten you thinking about it, but evidently you can't be wrong.
Rod cores have their uses, this isn't it. I hope this doesn't otherwise take away from our friendship.
Ordinary gapped RM cores are a very good basis for output filter inductors. They are available in the right sort of AL values (160 or 250 nH/turn), and are available in 3F3 ferrite, which works well at class-D switching frequencies.
Alternatively the range of precision-gapped ferrite toroids from Ferroxcube (designed especially for class-d output filters), have very low losses, although the core sizes available are only really of use for output filters for amps up to 250W or so.
I've had bad results from other toroidal powder cores. They work, but the core losses are too high for me to be happy with them.
Alternatively the range of precision-gapped ferrite toroids from Ferroxcube (designed especially for class-d output filters), have very low losses, although the core sizes available are only really of use for output filters for amps up to 250W or so.
I've had bad results from other toroidal powder cores. They work, but the core losses are too high for me to be happy with them.
Not all powder cores exhibit high losses, only the higher permeability low-cost ones do. MPP (Molybdenum Permalloy Powder) achieves reasonably high permeabilities and moderate losses (26u, 60u, 125u are best). Micrometals RF materials like "2" exhibit very low losses at the expense of low permeabilities. Several other Micrometals materials are a compromise between low permeability and low losses, but "2" is the lowest cost option.
Gapped ferrites have two main drawbacks: If the gap is covered by the windings, winding losses in front of the gap become very high due to the stray magnetic field from the gap inducing Eddy currents in the wire/foil. This is partially solved by using Litz wire (expensive and hard to source). If the gap is not covered by the windings, an undesirable strong stray magnetic field is produced because there is nothing acting as a shield in front of the gap.
I don't recommend gapped ferrites, at least not for compact high power designs. On the other hand, they are great for high current "pi" filter inductors where flux is not high and leakage is not a problem.
Gapped ferrites have two main drawbacks: If the gap is covered by the windings, winding losses in front of the gap become very high due to the stray magnetic field from the gap inducing Eddy currents in the wire/foil. This is partially solved by using Litz wire (expensive and hard to source). If the gap is not covered by the windings, an undesirable strong stray magnetic field is produced because there is nothing acting as a shield in front of the gap.
I don't recommend gapped ferrites, at least not for compact high power designs. On the other hand, they are great for high current "pi" filter inductors where flux is not high and leakage is not a problem.
Anyone looking for an off-the-shelf shielded inductor could look at the new SER2918H range from Coilcraft. This is surface-mountable and uses copper strip as the winding material.
Coilcraft (in the UK at least) will supply small quantities to hobbyists. Pricing is shown for most parts on their website.
Coilcraft (in the UK at least) will supply small quantities to hobbyists. Pricing is shown for most parts on their website.
Ouroboros said:
Interesting. Extreme low DCR. Do you have any experience with these?
I also stepped over this:
Ferroxcube Class D OF
Hmmmh: By looking at the filter calculations in above PDF I realized that I need not only to change the C in the filter if working with higher loads - as it is recommended in most of the e.g. Tripath datasheets.
For e.g. going from 4R to 8R I'd also need to double the size of the inductor according to above.
Is this correct?? How about 16R? And what is actually the result - soundwise - if working with the wrong filter size?
Cheers
One more:
Also interesting to see in above pdf, that on low power (<15W) applications as delivered by e.g. by T2020/T2021B the differences (obviously) and losses are quite small.
Which brings back the question if the air-core inductor for these low power amps wouldn't be the best choice.
And another obvious conclusion would be, that (small) digi-amps work best on high efficiency speakers due to lowest distortions/losses.
Cheers
Also interesting to see in above pdf, that on low power (<15W) applications as delivered by e.g. by T2020/T2021B the differences (obviously) and losses are quite small.
Which brings back the question if the air-core inductor for these low power amps wouldn't be the best choice.
And another obvious conclusion would be, that (small) digi-amps work best on high efficiency speakers due to lowest distortions/losses.
Cheers
I have four samples of the SER2918 in a 22uH size. I was looking at using these in a bridged 400W class-D (UCD style) amplifier to drive a 100V step-up transformer, but as they are very expensive, I'm going to use custom-wound inductors on RM12 cores instead.
The SER2918 range use cores of 3C92 ferrite, which is pretty good for use at class-D oscillation frequencies.
The SER2918 range use cores of 3C92 ferrite, which is pretty good for use at class-D oscillation frequencies.
The on-line purchasing facility on their website shows the 1-off price at $5.55. The first price break is at 250-off, when the price drops to $4.63 each.
It is true that to get an optimum match between the filter and the load, the filter component values need to be changed to suit. There are a number of free passive filter design programs on the web which will design a second-order Butterworth filter for you if you specify the source impedance (low), the load impedance, and the desired -3dB frequency. If you have access to a SPICE program (such as the simple 'TINA' available free on the TI website) or the fully featured LT spice available free on the Linear Tech website, then you can see the effect on the frequency and phase response when alering the load impedance.
( The free version of TINA is severely reduced in types of components, functional blocks and analysis features compared with the bought version).
I only use UCD-style amplifiers with post-filter feedback, which greatly reduces the effect of the filter termination load on the frequency response.
It is true that to get an optimum match between the filter and the load, the filter component values need to be changed to suit. There are a number of free passive filter design programs on the web which will design a second-order Butterworth filter for you if you specify the source impedance (low), the load impedance, and the desired -3dB frequency. If you have access to a SPICE program (such as the simple 'TINA' available free on the TI website) or the fully featured LT spice available free on the Linear Tech website, then you can see the effect on the frequency and phase response when alering the load impedance.
( The free version of TINA is severely reduced in types of components, functional blocks and analysis features compared with the bought version).
I only use UCD-style amplifiers with post-filter feedback, which greatly reduces the effect of the filter termination load on the frequency response.
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