This is great. It gets into the flux density and iron loss calculations that affect the physical size of a transformer core, choosing the wire, and then exquisite detail of actually winding and finishing the thing.
I need to spend a bunch more time reading this site.
(Also, Murray Gell-Mann was a whimsical character to begin with).
They tend to be much smaller, lighter, more efficient, cooler and cheaper. They also have features like adjustable output voltage, current limits, and overheat protection. Some can input and output AC or DC, at a configurable frequency and sometimes waveform. Some offer the same galvanic isolation that a transformer offers too.
The core of a switched mode supply usually is a transformer, or at least an inductor, but the key difference is that it operates at far higher frequencies than classic uses of transformers, which allows them to be far far smaller, and therefore cheaper for the same power output.
I designed a switching power supply a few years ago for a specialist application - driving 1930s Teletype machines which need 120VDC 60mA.[1] A switching power supply is a spike generator. Here's the schematic.[2]
This is reasonably RF-quiet. The transformer of the switching power supply is a toroid in a metal can, so you don't get too much RF from the transformer itself. But that's not where it usually comes from. The important thing is to keep spikes out of both the input and output wiring. That's dealt with by using LTSpice to simulate the circuit, and adding small capacitors and inductors until the spikes have disappeared in both voltage and current. At the output end, note the snubber C7, R1, D10, and D11, to soak up any spikes from the inductive load, and L2, to soak up output side current spikes. There's L1 and C12, to soak up kickback from the switched input side of the power supply. Plus C10 at the power input, which is from a USB port. They're all tiny surface mount components. The inductors are ferrite beads in surface mount form.
So there are eight extra components, just to prevent unwanted RF generation. The LTSpice simulation shows that they're all needed. The simulation was used to choose the values.
This is why good switching power supplies have more parts than bad ones. You see that in teardown videos.
[1] https://github.com/John-Nagle/ttyloopdriver
[2] https://github.com/John-Nagle/ttyloopdriver/blob/master/boar...
Eventually it will be worth switching out old transformers - they contain a massive amount of valuable copper and quite valuable steel, and their lower efficiency means every year they remain in service they are wasting $$$'s of electricity.
Transformers in cities can often be replaced with much smaller switched mode units underground, allowing the building housing the old transformer to be rebuilt as luxury flats to make the project much more profitable too!
Far different, but if you enjoyed this you may also enjoy another classic (which does not have explanation), Claude Paillard making a vacuum tube from glass and metal: https://www.youtube.com/watch?v=EzyXMEpq4qw
Okay this is what I come to HN for, thanks everybody!
Here's a more modern video on winding toroids by hand.[1]
I forgot how many windings it has, I think around 300 on the input side and 40 on the output.
Wiring it was a major pain in the ass, as the core is round, a closed circle.
And it draws too much current when idle, which means I have not used enough wire on the input side or the core is too small, fuck knows, I was 14 when I made it.
It does weld well, especially on DC through 4 huge diodes I also found in some scrap.
Sorry for my English, I'm drunk and tired.
