
A half century ago, better transistors revolutionized computer power supplies - kens
https://spectrum.ieee.org/computing/hardware/a-half-century-ago-better-transistors-and-switching-regulators-revolutionized-the-design-of-computer-power-supplies
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Animats
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.

[1] [https://github.com/John-Nagle/ttyloopdriver](https://github.com/John-
Nagle/ttyloopdriver)

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analog31
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.

~~~
hdiriekei
Quality micro amplifiers (class D) are extremely difficult to design.

They are way outside the possibilities of amateurs or boutique shops, unlike
classical amps (class A, ...)

~~~
kragen
What are the pitfalls?

~~~
analog31
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.

~~~
nwallin
Define "good enough oscilloscope"? A rigol 1054z can be had for $4-500. What
do you need from an oscilloscope that the 1054z doesn't provide?

I'm not saying you're wrong, I just don't understand.

~~~
analog31
That's probably good enough, but certainly better than what I have at home. In
fact, I bought a couple of those for my workplace.

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pjc50
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...](https://www.cirrus.com/company/media-
center/releases/2019/cirrus-logic-introduces-industrys-smallest-low-power-
boosted-smart-audio-amplifier-to-support-global-shift-to-mobile-stereo/)

~~~
kragen
*insulated

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hristov
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.

~~~
baybal2
> 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.

~~~
lisk1
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.

~~~
baybal2
Didn't know that. So they are saying bye to AC Propulsion people?

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jacquesm
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.

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ChuckMcM
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.

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Gibbon1
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.

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Retric
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.

~~~
pravda
I think in that specific case it's more due to improved battery technology.

~~~
kube-system
That's for sure. Those new small boost packs are using LiPos which are about
10x the power density of the old boost packs that were lead acid.

------
Stierlitz
“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.

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fortran77
> 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!

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rwallace
> 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?

~~~
colanderman
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.)

