Swiching power supplies are much more efficient, both in operation and in manufacturing. They use a lot less resources to manufacture.
That is what the world needs more than clean HF bands. Live with it.
Then you probably had one of those lucky situations where there was shunting impedance to ground. :-)
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Gee, it's great that there are people like you, People Who Know Best. Otherwise we the great unwashed would have no one to tell us how to think, and then where would we be?
There's nothing that prevents one from making quiet switching supplies. They just cost more.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
It's not just the HF bands. A few years ago, we were helping the county radio shop track down a noise source that was trashing the input to one of their VHF voting system receivers. It turned out to be a switching power supply running some LED lighting about 1.5 miles away. Something like these: Someone tore it apart and determined that there was little in the way of RFI protection on either the input or output. However, that wasn't the real problem. The PWM chip had a feature called "spread spectrum" where the RFI generated is spread over a much wider bandwidth, resulting in reduced peak power. In effect, it takes some fairly narrow band radiated switching junk and splatters it all over a wider bandwidth. The FCC allows this because some brilliant attorney decided that only the peak emission level was important, not the overall power belched by the interference source. So, you're right... the world needs more than clean HF bands. It needs a non-political FCC.
About 30 years ago, a few people saw what was coming and tried to convince the FCC and the ITU to allocate specific frequencies for switching power supplies. Such a frequency would be declared the dumping ground for switcher RFI, such as 13.56MHz. We worked out a preliminary frequency plan, which was far from ideal, but at least a good start. The idea was summarily killed when the spread spectrum trick was accepted by the FCC as the "solution" to the EMI/RFI problem.
So, while you're enjoying your switcher powered gizmos and gadgets, there are a few of us that are doing what we can to clean up the mess that your attitude seem to have left behind.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
It has never been very appealing, in my wannabe HAM days they mostly exchanged RST reports. Several days of listening to the real HAMs entirely killed the desire to obtain my own license. I wanted to build devices, not to become a protein-based RSSI.
But they moved from designing electronics to connecting modules. Sometimes the results are very spectacular, but, on the other hand, no ready-made module == impossible. Still much better that listening to Bieber, though... Best regards, Piotr
Germany and a fair fraction of Europe work thanks to the AM transmissions (DCF77@77.5kHz for time broadcast, DCF49@129kHz for remote control of power meters etc.). Unfortunately, the lower LF band is where the EMI is highest. There are PM signals too, but no consumer-grade devices use that due to the involved complexity. There is also LORAN, but it is not very useful on land.
Best regards, Piotr
But would it ever work? The frequency of the switchers is mostly limited by the magnetics and then by the MOSFET drivers/losses. That puts them in the 50kHz...1MHz band, which is/used to be densely populated. They use square waves of variable duty cycle, with the harmonic garbage way above their "baseband". The resonant soft switchers are a novelty from the mass market perspective. So how would a static allocation of, say,
100kHz help here?Best regards, Piotr
Over a mile away? Did you sic the FCC on them? Good point, though, they should ban all those new fangled fluorescent and LED lights and go back to good old tungsten.
Nonsense. Receivers are sensitive to the in-band energy. Spreading it out *helps* EMI. It has other issues but it does do exactly what it was intended to do. BTW, EMI tests aren't just peak tests. The unit has to test quasi-peak and average masks, as well.
Which would do absolutely nothing for harmonics (the real problem) unless all of the harmonics of your magic switching frequency were also reserved. 13.56MHz would be rather useless as a reserved switcher frequency, considering that this is rather high for the fundamental (see above for harmonics).
The issue is proper design. It can be, and is, done. Some industries have stricter limits than the FCC's and they deal with switching power supplies without too much trouble.
Not too self-important. No, not you!
Oh, I assumed the common mode got in at the source. The computer ground (or something) was bouncing around.
George H.
I'm fairly sure the scheme would work if the switchers were frequency stabilized with either a crystal oscillator or ceramic resonator. Same as with any uP or clocked device. Most of the energy would be in the fundamental and 3rd harmonic. As the harmonic frequency increases, it becomes easier to shield and filter.
Square waves have 67% of the energy in the fundamental, and the remaining 33% in odd order harmonics. As the duty cycle changes the waveform become asymmetrical, producing more and more even order harmonics. Eventually, for really low duty cycles, it becomes a pulse train which produces a comb line of equal power signals.
Obviously, we're not suggesting that all switchers operate at
13.56MHz, which incidentally was one of the original diathermy frequencies. There are other frequencies, but none low enough to be usable in a switching power supply: So, we had to find an empty frequency and go through the ordeal process of getting the FCC, ETSI, CEPT, and later the ITU to allocate or reassign new frequencies. At the time (about 1977) it was apparent that the long wave marine navigation beacon band (160KHz to 530KHz) was eventually going to be replaced by NAVSTAR (now known as GPS) system. Since it was expected to take at least 20 years to get approval for a reallocation of the LW spectrum, this was a reasonable strategy. As it turned out, most of the US beacons were turned off in 1997, almost exactly 20 years later. There was also a problem with the US Navy, which wanted some of the low end of the LW beacon band for submarine communications. However, none of this happened when spread spectrum PWM power supply modulation arrived and killed the plan.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Nope. Complaining to the FCC doesn't work unless one has a VIP (very important person) behind the complaint. Basically, the FCC is out of the enforcement business, which is now handled by the Dept of Justice, which won't touch any case unless the recovered fines exceed the cost of investigation, enforcement, and the inevitable compromises. If I had discovered something that might generate a few thousand dollars in fines for the Justice Dept, I might have gotten their attention.
Personally, I prefer candles, natural gas, and kerosene lamps. The solution to technical problems is usually not to ban the new technology.
Look at a spread spectrum clock on a spectrum analyzer: Some PWM chips have a spread spectrum (SS) on/off pin or function. Try it both ways. What you get with SS turn on is something like the photo: What you get with SS off is a single coherent frequency, but with an amplitude equal to all the energy (area under the curve for each sideband) piled on top of the fundamental. However, you're right about SS helping EMI. Few of todays clocked devices would ever pass EMI/RFI testing without it.
Agreed. Ideally, all the harmonics would be reserved. However, since the fundamental would probably need to be a fairly low frequency (50Khz to 2MHz), the number of reserved frequencies needed to handle the harmonics could easily be huge. The assumption was that the higher harmonics are easier to filter with ferrite beads and easier to shield. I don't recall how many harmonics we expect to ask for allocations, but I think it was 11.
They have stricter limits today because the FCC limits didn't work for them, partly because they allowed spread spectrum clock modulation. Please remember that this was about 1977 and the life was a bit different. We didn't have decent power MOSFETs, IGBT devices, SiGe, and silicon nitride devices. Most switchers of the day used BJT, crude IC's, and no spread spectrum.
Sorry. There are a few topics that produce an emotional response, instead of a technical discussion. This is one of those and was a source of frustration for many years. I usually try to suppress my emotions but lost it this time. I'll try to be more diplomatic in the future.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Even without any filtering the interference would be confined to a list of frequencies. Perhpas it could even have done away with the need to filter a t all?
You could maybe cater for a range of SMPSU frequencies by permitting eg unf iltered operation at a ladder-like range of frequencies, leaving at least m ost of the spectrum free of junk, rather than just one frequency, which wou ld never work long or medium term.
NT
That assumption is simply wrong. It's never the fundamental or third harmonic that's the problem, rather the 101st. The problem is almost always in the parasitics around the switch node. Snubbers help but layout is the key.
Irrelevant.
The idea is simply nuts. It's not surprising no one listened.
Yet that's what you're proposing.
Oh, good grief!
OF course they do. Are you daft?
YEs, and a receiver is sensitive to the area under its sensitivity curve, too. The idea is to spread the interference signal further out than the interferred.
It's not uncommon for the interference to be the 100th harmonic, or even higher. I've seen combs into the FM band and above.
Who cares about "of the day"? Even so, you're talking about 13MHz, which would have been silly in 1977.
Thanks for the info.
The RIF-Ham.pdf is very helpful.
Palomar-Engineers that's a name I haven't heard in years, I have a box of cores from them that I got in the mid 90's. I see they have a wall wart kit for EMI, it's under this link:
The Clip on bead they use (square one) looks like the Lab favorite from Fairite, the one I have does not have the PN on it anymore. I've done the multi-turn thru the cores before ( like George suggested) with success, but these SMPS's are just screamers and hard to easily suppress.
The last RFI problem I had was with one of those 12DC auto cell phone chargers for a Nokia phone. Wound up putting a multi turn bead on and loading the output with 0.1uf 0.01uf and a 100uf capacitor. What was interesting was that the little switcher they used was not wired per the data sheet for the Nokia phone, once I wired it for my Motorola phone (5V) it created nice birdies in the AM band.
Cheers
That's all I could find while eating dinner. This article explains it in more detail and with nicer looking spectrum analyzer screen shots.
Right and spreading the signal over a wider bandwidth allows it to interfere with more narrowband receivers operating on adjacent channels. Instead of trashing one receiver, the SS noise causes problems with all of them. Of course, the noise power bandwidth will be less, so the interference would be less, which is why the FCC accepted the idea. Whether this is a good tradeoff is subject to considerable debate.
Sure, but like I previously muttered, a common ferrite bead on the in/out wires can stop 100 MHz trash quite easily. Trying to do the same at 100 KHz would require a much larger ferrite bead. If you're seeing a comb line at 100 MHz (assuming the harmonics weren't created in the spectrum analyzer front end from overload), then someone didn't do a very good job of designing the switcher.
I was commenting about the lack of modern solutions, techniques, and devices that were not available in about 1977 when we were working on a political solution.
Yep. See my comments elsewhere about the selection of frequencies and the lack of harmonically related possibilities among the ISM frequencies. Basically, we were trying to have allocated marine LW beacon band frequencies and their harmonics after the LW beacon band transmitters were shut off. The allocation of RF spectrum is normally not done for the convenience of power supply manufacturers and we didn't have even a preliminary list of usable frequencies. 13.56 MHz would probably have been a harmonic of some lower frequency.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Y'er welcome.
It's RFI-ham.pdf. It is much better than most articles on RFI/EMI suppression because it has a good mix of theory, experience, tests, and sources.
I'm not sure of the current status of the company. The owner died in
2013 and things seem to be rather confused since then: You can probably build all of the ferrite filters and chokes yourself.The smash-on split bead variety are quite common and cheap: However, you can get more turns and heavier gauge wire through a large toroid.
I built constant current dummy load for testing power supplies and chargers. These should work better than my mess: (I just ordered one of these) At some point along the load curve, I can often get a cheap Chinese bottom of the line charger to go unstable and oscillate.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I'm not "the one who knows best", I am the one that realistically sees that the use of frequency bands in the world has irreversibly changed.
In the past the HF bands were used to do radio transmissions, now they are emitted as unwanted byproduct by modern equipment, and they are no longer used for radio. At least not like before.
For sure it would be good to design switching supplies with low emission, but don't think that would solve the problem of "HF bands not being as quiet as they used to be". There are too many other sources of emissions that are not so easy to handle. E.g. ethernet over powerline.
One can argue that many of them are just "bad ideas" and "irresponsible engineering" but it is just irrelevant in a world where nobody cares about HF radio reception except some old-hat radio amateurs. In the modern society they are irrelevant and only hampering innovation.
I know, I have clocks like that and I am seeing all the time how they have more and more difficulty receiving the signal.
Both at home and at work, the reception of DCF77 is erratic at best:
remote refid st t when poll reach delay offset jitter ============================================================================== GENERIC(0) .DCFa. 0 l 289m 64 0 0.000 -0.717 0.000
So, I now use GPS as a reference.
But they are just consumer products, they can fail without many serious implications. Remote meter switching for the purpose of proper bill calculation is another story, can end with a lawsuit.
GPS requires direct sky visibility, which sometimes is a serious problem. The VLF signals can be received easily deep in the concrete buildings, it's just the noise that makes it hard to decode.
Best regards, Piotr
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