Switching power supplies are a simple idea complicated to do well. The concept is an inductor and a switch across the input. Close the switch, and the inductor's magnetic field builds up. Open the switch, and the inductor tries to maintain constant current by producing a high voltage. If the input side inductor is part of a transformer, you can get a higher or lower voltage out as the magnetic field collapses. That's an auto ignition from the mid 20th century.
That approach suffers from arcing at the switch points, blithers all over the RF spectrum, and wastes energy by keeping the input on too long. Progress since then focuses on solving all those problems, plus some others.
Power MOSFETs provided an electronic switch with a really low ON resistance, in the millohm range, an OFF resistance in the kiloohm or even megohm range, and a switching time fast enough that you don't spend much time between ON and OFF. At very low resistance, almost no energy is dissipated in the switch, and at very high resistance, almost no energy is dissipated in the switch. Between those points, the switch loses energy through resistive heating. This is why switching power supplies get warm. The less time spent transitioning between OFF and ON, the less heating.
A switching power supply is almost a dead short across its input if the switch stays turned on after the inductor reaches magnetic saturation. This is why switching power supplies can burn up or catch fire. Failure of the power MOSFET (and they usually fail ON) or the control circuitry is big trouble. Which is why they need protection circuitry. This is what UL approval is for. Along with insisting that the input and output windings of the power transformer have enough insulation between them, so you don't get power line voltage at the USB jack.
In most other areas of electronics, you avoid generating spikes. Switching power supplies generate big spikes on purpose. Getting the energy of those spikes into the output capacitor is what it's all about. The energy can leak out as spikes on the input side, spikes on the output side, loud RF noise, or heat. Getting all those under control requires some extra parts. Surface mount ferrite beads and chip capacitors, mostly. Things you usually don't have to think about, such as the inductance of capacitors, are big issues. This is what FCC approval is for.
I designed and built a special purpose switching power supply a few years ago, and it's on Github. [1] There's a detailed explanation of how it works, including what all those minor parts do. The traditional linear solution to that problem is about 5% efficient, runs hot, and much larger.
Interestingly, the same transistors have revolutionized audio amplifiers. I'm a musician, and typically play with an amplifier. Over the years, my amp has gone from 40 pounds of steel, copper, and vacuum tubes, to a 15 pound solid state amplifier, to a 2.5 pound switchmode amp, with no loss of tone quality that I can perceive.
The rise of the new "micro" amplifiers has been driven in no small part by improved MOSFETs that can switch faster and more efficiently, at higher voltages. I can't imagine that demand for musical equipment drove this development, but we certainly benefit from it.
Also a guitarist. I own 3 amps, two tube and one hybrid. Used to have a solid state. You really can't tell the difference? It's night and day to me, even with the newer Fender mustangs that have great models.
I won't turn in my HT40 for a solid state until Kempers can deliver the same quality at the same price (which I picked up off craigslist for $400). Now my little mono price 15W (which is loud as hell) sounds pretty terrible in most settings but I haven't found a solid state that can give the same character with the right settings. Plus real spring reverb, i can't kick a DSP to make it jangle.
If you're talking acoustic sure solid state wins every day of the week. But in the mid tier amp market for electrics tubes win out.
I do think though that most people don't know how to use a tube amp to get a good tone though. Crank the power amp volume and use your gain as a volume control, push the input with a clean boost or light drive to get distortion. The harmonics stack through the chain, and that's how you get the crystal clear sound without being drowned in noise or fuzz. It's also something you can't do on a solid state, since the input is buffered and the DSPs don't really handle that idea well.
I firmly believe that DSP could emulate any guitar amp. If it's real, then it can be measured, and if it can be measured, then it can be simulated.
What I think is the big deal is, an amp might be capable of producing a certain tone quality, but that tone quality is unreachable if the controls don't cooperate or are not intuitive. It's a user interface problem. What's more, if it's frustrating to the guitarist, they will notice even if the audience (or the bassist) doesn't.
I also think it's a non-problem to some extent because tubes are not prohibitively expensive, and guitar amps don't need to be exceptionally powerful.
> I firmly believe that DSP could emulate any guitar amp. If it's real, then it can be measured, and if it can be measured, then it can be simulated.
This is absolutely true, but the possibility of it doesn't tell you anything about someone having been successful at it.
One way to think about is that the market for the product can be split into three populations: Those who will buy even if the simulation is poor (they can't tell, don't care, or buy based on price or other wizbang features), those who won't buy no matter how good the simulation is (they don't care about the cost/weight/power, are happy with the classic stuff, ones snub simulations for social reasons, ones who prefer products without long boot times or with physical knobs, or just can't tell and are going to be conservative), and those who would buy but only if it's good.
I think in many cases this last group is much smaller than the other two. As a result it doesn't necessarily make commercial sense to make the simulation especially good.
Even in the case of linear effects (e.g. typically reverbs) where it's easy to measure them and determine scientifically that any difference would be (nearly-)inaudible there are many implementations that don't even bother to try being particularly faithful. For non-linear effects like guitar amplifiers it's much more difficult to objectively characterize their performance.
[I own no tube amps or other similar things, but I understand why people do.]
> those who would buy but only if it's good.
>
> I think in many cases this last group is much smaller than the other two.
Maybe, but the professionals have spoken and deemed the modeling amps "good enough". Lots of them now regularly tour with a modeling amp so they don't have to carry a half-ton of equipment and risk their precious vintage amp in the hands of stage and transport monkeys.
And, I might concede that tube amps sound better than solid state ... if you have one of the "stage queens". Marshall's and Mesa Boogie's, for example, are notorious for having a few exemplars in a line that sound great, but the vast majority of them are just kind of "meh".
The modeling amps allow you to always have the "stage queen".
Indeed, and an additional issue is that success is impossible to measure. Objective testing (double blind or whatever) is prohibitive, and there's a tradition of judging gear based on subjective opinion, that will be hard to overcome. We could already be past the stage where the simulations are good enough, and never know it.
Commercial success might not be driving the development of these products. Anybody who's that good with DSP could make more money outside of the musical instrument business. Someone is doing this because it's their passion.
There are plenty of folks who research this problem at the manufacturers as well as in academia. Stanford, McGill, NYU, UMiami, Aalto University, are a few places where you can find great researchers. The leading journals are the jAES and DAFX journal, and in industry I know of Fender, Native Instruments, Waves, IZotope, among others that were hiring PhDs for this kind of role in the last year. Decent money, not SV money however, but it's more honest work than going to study audio projects for DARPA contractors.
It's a deceptively tricky DSP problem. The surface issue is that nonlinearities create harmonics that wrap around the Nyquist frequency, which creates aliasing. To deal with it you oversample, which introduces some frequency/phase distortion, and in the cutting edge solutions they run at 8-16x oversampling (which means 8-16x more CPU cycles for the distortion algorithm). And it gets worse with heavier distortion.
On the algorithm side there has been some crazy good work with creating black box models using Volterra Series and dynamic convolution, but it's an O(n^2) algorithm (although I believe there's an O(logn) solution out there). The top of the line modeling amps (mostly Kemper, there are a few others) use these approaches among others to give you hundreds of amps at your fingertips, and they sound great. Plenty of high profile bands use them, Metallica probably the most prolific.
I bet someone has applied convolutional neural nets to the problem, since I'd suspect they're exceptionally well suited for black box modeling of nonlinear distortion. Sub in an atan(kx)/atan(k) for your activation function and each neuron would be it's own first order model of a tube stage. The asymmetry might be more difficult to handle, which is where a lot of the warm tube goodness comes from.
The UI problem is well known. That's really what sets one amp design apart from another. No tube amp is particularly unique in signal path or component choice, the ability to dial in a tone is the secret sauce behind the classic designs imo, also why some newer models from Marshall are so much worse than newer guys on the block, but that's just my opinion.
Because upsampling requires interpolation. I'm using distortion in the abstract/academic sense here.
Any signal through a non ideal (or nontrivial, eg a gain) system will introduce distortion, harmonic being new energy at different frequencies, frequency distortion in the relative magnitude at the output that is different than the input, and the same for phase.
If you use a polynomial interpolator there will be harmonic distortion. If you use an interpolation filter there will be frequency distortion, which is highly correlated to the phase distortion.
What that distortion is and if it is perceptible depends on your design and constraints. But the key element that is at play here is that oversampling for nonlinear system modeling, which introduces harmonic distortion after the fact, is that it can amplify frequency (and therefore phase) distortion and your constraints are tighter than they normally are.
If you want an example take a the ideal interpolator, which is a sinc function. Because a true sync is non causal you cannot implement it, therefore lossless interpolation is not achievable. There will always be some loss of information, the design problem is trading off that loss with the resources required. We can do pretty damn good upsampling today however.
One thing that might work in our favor here, is that for this particular application -- simulating a guitar amplifier -- we are only dealing with the subset of behaviors that are physically realizable in an electronic circuit.
Class D (or Class T) amplifiers are just switching power supplies "turned sideways." By which I mean that the important input changes from the AC power to the regulation signal. The latter is a DC reference voltage in a power supply; it's the audio input in an amp.
Owning a good enough oscilloscope is actually an issue. The switching signals are high speed, and subtle variations impinge on both the efficiency and stability of the amplifier. Many of the components are operating in their regime of non ideal behavior, e.g., a capacitor is not just a capacitor. Circuit board layout is also a big deal.
Even the commercial amplifier makers have mostly reverted to buy-in modules. Most of the "mini amps" sold for bass guitar contain IcePower modules made by a division of Bang & Olufsen.
I've gone so far as to simulate a switchmode amplifier in LTSpice just for fun. I'm quite heavily into electronics, but have made it a personal rule not to mess around with homemade line powered equipment that I would actually take to a performance. I don't want to become known as the whiz kid whose homemade gear blew up on stage. ;-)
At lower power levels, there are some IC's made by Texas Instruments and others that shouldn't be too difficult to apply, but you can also get entire amplifier boards with these chips from online suppliers for next to nothing.
Not for testing a class-D amp, which switches in the MHz range, and you do want to test if it's stable, if your filters actually get rid of the HF parts, ... And even for an analog design 50kHz wouldn't really be enough for many potential problems which happen above that. Worrying just about the audio range is not enough.
Indeed, and it's the high frequency behavior where you see if you're getting charge on and off the gates of the MOSFETs fast enough with just the right timing.
There have been subsequent revolutions too: the silicon carbide MOSFET, which supports much higher voltages, and the IGBT (integrated gate bipolar transistor), which have done the same thing for much larger power electronics such as those in electric cars.
Switchmode power supplies have also benefited from better microprocessors allowing control of temperature, peak current, etc; my employer has done some neat tricks integrating this into audio amplifiers for phones. https://www.cirrus.com/company/media-center/releases/2019/ci...
Currently there is a new wave of better transistor technology, that should hopefully make our power supplies better. For example, Gallium Nitride transistors in combination with System in Package technology and spintronic isolators could and should revolutionize consumer power supplies again. Unfortunately, this area is not considered too sexy and does not get too much investment.
But hopefully, they do get around to it. I can't wait to get rid of the power bricks.
> Unfortunately, this area is not considered too sexy and does not get too much investment.
You are getting it better than the rest of the world. Power electronics is once of the last semiconductor niche where US has both the edge in already, and a prospect for future growth.
You have to thank your military for that. Military use power electronics is a giant market in USA, but it's also a very pathological one. US military buys simplest bucks and boost circuits (for non-engineers, those things amount to "power electronics 101") for few thousand dollars a pop.
Few months ago, I had a chat with BYD engineers about their own power electronics problem. The best China got domestically are few generations old IGBTs. E6 for example has a 89% efficient powertrain, as I was told. The only Chinese power electronics company on the road to SiC I know is IVCT, and I haven't seen them showing any life signs for quite some time.
They want to eventually do their own power electronics, or at least fully own it from the packaging/integration stage.
You can see how far Tesla went in Model S to Model 3 inverter design when they switched to SiC switches. Model 3's inverter is microscopic in comparison to Model S ones. And apparently, it's also more efficient at the same time, without any extra tricks used.
Probably the thing you dont know about Model 3 motor inverter is that its designed by a Dutch company and uses ST Microelectronics power mosfets manufactured in fab in Italy , Tesla is also considering second supplier for power mosfets, Infinion technology again European based electronics components manufacturing company.
For those of us who travel a lot, GaN is fantastic! They are inexpensive, tiny and light weight. I got a $35 61w usbc adapter and it has no problems keeping up on my macbook pro 15" and is a fraction of the weight/size as the apple brick.
Ditto for welding equipment. A switched mode stick welder weighs next to nothing and will happily max out whatever socket you plug it in to. Steady as can be too under fluctuating load.
They are marvels, and today's MOSFETs make for even smaller and lighter supplies. They bring noise with them though, so you will often see switching supplies that take line voltage down to some lower DC voltage, and then a crap ton of filters, connected to a linear supply that gives you the desired voltage in RF circuits.
Definitely power transistors are one of the most important developments of the last 50 years that most people don't know about.
They enabled not just computer power supplies but also variable frequency drives for electric motors. That saved enormous amount of energy. And made things like electric cars practical.
A related advancement is handheld car jump-starters have gotten cheap and tiny. They frequently include USB charging ports etc due to those same transistor advancements coupled with improved battery technology.
Yeah a hand held jump starter is like $40-60. I have one that was left in my car when it got recovered after being stolen. Works great. Also doubles as a USB charger and flashlight.
As long as it has enough charge to do its job when required. What type of batteries are in these, and how long do they hold appropriate charges? I've seen these smaller starters in stores that I immediately dismiss them as useful (dollar stores etc).
What I found is that if the car battery is completely dead they don't work. So they aren't a complete replacement for jumper cables. But I've left the lights on, battery dead. And the hand held jumper got my van started.
I don't know how long the batteries last. I assume they use lithium polymer batteries. Mine I just keep it plugged in all the time.
Let it sit for a few minutes before attempting to crank the car otherwise the starter motor and the battery are in competition and that leaves too little for the starter motor. First you need to bring the battery up to a voltage higher than what's left under maximum load by the starter motor. 10V should do it for most cars.
They all use some flavor of lithium. The one I got ( https://smile.amazon.com/gp/product/B0748D8KT6/ ) holds its charge well. I keep it in my glove box, and even charging it every few months, it only drops down one light out of five. The largest vehicle I've started with it was a V-10 gas Ford truck, and it worked without issue. I was genuinely impressed.
I just used my Noco 1000 Amp to help some guys in a parking lot on Friday. The last time I had charged it was many months ago, maybe a year. Came on at full power and got the car started in 30 seconds. Big fan.
so what are these manufacturers doing that allows a LiPo to keep power for that long with no maintenance charges? I have to remember to plug in my RC batteries periodically as well as my camera batteries to keep them from becoming useless.
“Instead of a conventional linear power supply, Holt built one like those used in oscilloscopes. It switched the power on and off not sixty times per second, but thousands of times; this allowed it to store the power for far less time, and thus throw off less heat.”
Not exactly, the power is stored in an inductor and fed to the load, the inductor being topped-up by switching the unregulated rail on-and-off thousands of times a second.
> As a tech enthusiast, you probably know what microprocessor is in your computer and how much physical memory it has, but odds are you know nothing about the power supply.
Ummm...tech "enthusiasts" generally spend a lot of time choosing the power supply if building a PC!
> For example, in 1962 the Telstar satellite (the first satellite to transmit television pictures) and the Minuteman missile both used switching power supplies.
I thought switching power supplies were for converting high voltage AC to low voltage DC. I would have expected a satellite to run off solar panels and missile electronics to run off batteries, both of which already produce low voltage DC. What am I missing?
SMPSes are also used for DC/DC conversion (up or down). Especially with solar panels, they are mixed current/voltage-mode devices, so you want to load them at a specific voltage (which depends on the incident light) to maximize the power draw. (This is what a power optimizer does in a solar panel installation.)
That approach suffers from arcing at the switch points, blithers all over the RF spectrum, and wastes energy by keeping the input on too long. Progress since then focuses on solving all those problems, plus some others.
Power MOSFETs provided an electronic switch with a really low ON resistance, in the millohm range, an OFF resistance in the kiloohm or even megohm range, and a switching time fast enough that you don't spend much time between ON and OFF. At very low resistance, almost no energy is dissipated in the switch, and at very high resistance, almost no energy is dissipated in the switch. Between those points, the switch loses energy through resistive heating. This is why switching power supplies get warm. The less time spent transitioning between OFF and ON, the less heating.
A switching power supply is almost a dead short across its input if the switch stays turned on after the inductor reaches magnetic saturation. This is why switching power supplies can burn up or catch fire. Failure of the power MOSFET (and they usually fail ON) or the control circuitry is big trouble. Which is why they need protection circuitry. This is what UL approval is for. Along with insisting that the input and output windings of the power transformer have enough insulation between them, so you don't get power line voltage at the USB jack.
In most other areas of electronics, you avoid generating spikes. Switching power supplies generate big spikes on purpose. Getting the energy of those spikes into the output capacitor is what it's all about. The energy can leak out as spikes on the input side, spikes on the output side, loud RF noise, or heat. Getting all those under control requires some extra parts. Surface mount ferrite beads and chip capacitors, mostly. Things you usually don't have to think about, such as the inductance of capacitors, are big issues. This is what FCC approval is for.
I designed and built a special purpose switching power supply a few years ago, and it's on Github. [1] There's a detailed explanation of how it works, including what all those minor parts do. The traditional linear solution to that problem is about 5% efficient, runs hot, and much larger.
[1] https://github.com/John-Nagle/ttyloopdriver