Apple didn't revolutionize power supplies; new transistors did (2012)

6/12/2026 at 7:55:24 AM

> requiring transistors that can efficiently switch on and off at high speed under high power.

Right. Switching power supplies need to go from off to on fast. In the full on state, the resistance is near zero (millohms with modern MOSFETs), and there's little heat dissipation. In the full off state, the resistance is near infinite (megohms with modern MOSFETs), with little heat dissipation because the current is near zero. During the transition, the switching element dissipates power as a resistor. The less time spend in transition, the less heat generated and the higher the efficiency.

Today the components are so good this is easy and efficiencies have passed 90%. That wasn't true in the Apple 2 era. Power transistors had higher OFF resistances, lower ON resistances, and slower slew rates. The better power transistors cost more. A cost-effective power supply that wouldn't overheat was tough to engineer.

(I've designed and built a switching power supply. Worked fine, could handle no-load and a dead short, and didn't blither all over the RF spectrum. Probably had twice the parts cost a good designer could achieve.)

by Animats

6/12/2026 at 7:13:52 PM

Correction: lower OFF resistances, higher ON resistances. There was heat generation even outside the transition period.

Every modern locomotive motor is powered by a switching power supply. The transistor packages are about 10x20cm. You could hold one in your hand. They're not super-expensive. They're smaller than a mechanical switch of the same rating.

MOSFETs are insanely good switches. It's amazing that's physically possible.

[1] https://publisher.hitachienergy.com/preview?DocumentID=5SYA1...

by Animats

6/11/2026 at 9:09:10 PM

Previously:

(2012, 246 points, 74 comments) https://news.ycombinator.com/item?id=3636047

(2013, 170 points, 63 comments) https://news.ycombinator.com/item?id=6575994

(2021, 208 points, 158 comments) https://news.ycombinator.com/item?id=28700554

by js2

6/12/2026 at 12:09:55 AM

The Apple II power supply was the first switching PS I had ever seen. And I still saw a lot of linear ones post-Apple II… From the article, perhaps the IBM switching PS, four years after the Apple II, then more or less cemented the switching PS for consumer electronics.

by JKCalhoun

6/12/2026 at 10:36:00 AM

Are switching PSUs more expensive to produce than linear ones? Because, if you think about it, they took several decades to move from higher-end to lower-end products: my Atari 800XE (the third generation of the Atari 800, introduced 1985, so 8 years after the Apple II) still had a linear PSU. So did most cheaper mobile phones (most prominently the good old Nokia feature phones) up until around 2005.

by rob74

6/12/2026 at 10:48:09 AM

Yes for a few reasons: more components, more noise filtering needed for sensitive devices, and more design theory and analysis is needed. A linear supply is nothing more than a high current op-amp. A switching supply requires understanding currents in the time domain to choose or design the right inductor. It's just more.

However, they don't need the same heatsinking as linear supplies, so they're less expensive in that regard. If designing an optimal heatsink (which has the second order effect of determining what else around the part will heat up because of the regulator) is a lot of work, then maybe the NRE will be the same. But overall linear regulators are fewer and simpler components so the BoM cost is a lot lower.

by Neywiny

6/12/2026 at 11:18:14 AM

The materials in a 60hz transformer I think are the main BOM cost for linears? Relatively, transformers are say 2x cheaper than in 1970 (steel and copper are relatively MORE expensive than they used to be but the manufacturing improved) - but chips are more like 100x or 1000x cheaper. The high frequencies of switchers let you shrink the transformer (less materials) so its a big win.

Also the waste heat of linears constrains your design in terms of weight, power density, how big you need to make the enclosure, etc.

For reference I looked at what I'd need to buy on AliExpress to power my laptop off the cheapest linear PSU I could find (say 20v 5A), something like: https://www.aliexpress.com/item/1005003397909174.html - it weighs 4kg vs 300g for the charger I have. Apparently there ARE audio people who put their NAS on a linear PSU (I did not realise that was a thing!) but I'm going to try to forget I saw that.

by xyzzy123

6/12/2026 at 4:49:36 PM

Switchers in the 80s were only 80% efficient at best. The chips just weren't fast enough for much better.

Switching from maybe 70% efficient linear to 80% efficient switcher means only a 30% reduction to copper or transformers.

-------

Today, a switcher is maybe 95% to 99% efficient. So switching from 70% efficient linear to 97% efficient switcher is a 90% reduction in coils/heat sinks.

by dragontamer

6/13/2026 at 1:25:00 AM

Switchers have much smaller transformers because the frequency is much higher, >20 kHz vs 60 Hz. (This is the same reason that avionics use 400 Hz power instead of 60 Hz.)

by kens

6/12/2026 at 7:49:42 PM

> Are switching PSUs more expensive to produce than linear ones?

They were, back in the day.

Around the time the Apple II came out, a (linear) power supply wasn't cheap, but robust. And machines like it were way more expensive than its PS. The complexity of a switcher would affect that cost ratio. So few manufacturers bothered to make the PS as small or efficient as it could be.

But computers became cheaper, some more power-hungry, switching PS designs advanced (and cut down weight, size & the amount of copper needed), and markets grew. And effiency became a thing (see eg. EU regulations). So the economics made switcher designs trickle down to ever smaller & smaller power supplies.

(the latter is still ongoing btw)

by RetroTechie

6/12/2026 at 7:05:17 PM

Switching PSUs have significantly more complicated chips, linear PSUs have significantly bulkier additional components. This means early switching PSUs were expensive while modern switching PSUs are dirt cheap.

by crote

6/12/2026 at 4:11:11 AM

Jobs mischaracterized the innovation, and the author is technically correct (the best kind), but it's a shame that the piece appears to want to bury Holt's actual accomplishment. Holt's work was innovative in the same way that Woz's Disk II controller was. He didn’t invent the underlying technology, and he did create an elegant, product-defining implementation of a known (but difficult) technique.

by CharlesW

6/12/2026 at 6:20:12 AM

Author here. Can you clarify what you consider Holt's innovative power supply accomplishment to be? I spent an excessive amount of time studying Holt's power supply to find out what made it special, but couldn't find anything particularly important.

by kens

6/12/2026 at 8:33:27 AM

Yeah it's nothing special. I find the whole Apple innovation thing quite tedious if I'm honest. I've seen some milspec stuff from around that era that purposely misused an LM723 as an SMPS. This was done without any fanfare at all even though it was quite interesting.

by cryo32

6/13/2026 at 4:02:06 AM

I wouldn't put Holt's power supply on the same pedestal as the Woz drive controller which I feel was actually innovative but perhaps what the angle they are looking at is just the apparent dearth of switched mode power supplies in the market for home computers, games etc at that time. If I think back to that time, Atari, Commodore, Radio Shack, TI etc - they all used heavy transformer bricks and linear regulators. I think the BBC microcomputer went to an Astec switch mode supply after a brick on launch and that was in 1982. Maybe it was this rise of Astec that you can somehow attribute to Apple and Rod Holt after a fashion.

by djmips

6/12/2026 at 6:56:57 AM

I second your analysis, there's nothing special at all about it. By the standards of the time it was a unusual to see a switch-mode supply in a computer, but the supply itself isn't unique when compared to contemporary designs. Mix "unusual application of a known technology" with "Apple fanboyism" and you get "Holt revolutionized power supplies" or whatever the claim is.

by ryukoposting

6/12/2026 at 7:26:25 PM

From that quote @ start of the article:

"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."

Aargh who wrote that?!? (not Jobs himself, I hope). Electronics designers everywhere grab their vomit bag.

Anyway, good read & well researched by Ken (as always).

by RetroTechie

6/13/2026 at 1:28:14 AM

That was written by Walter Isaacson, who wrote the biography of Steve Jobs.He is a good writer, but that description of a switching power supply is very messed up. You can see the right ideas inside there, struggling to escape.

by kens

6/12/2026 at 7:20:04 AM

Not sure what is the puzzle here: the most likely explanation is that Holt himself had very narrow historic knowledge of the provenance of the design he had learned off when doing oscilloscope power supply design, told his boss Jobs, and he then just repeated like a parrot what Holt told him.

Contemporary example would be a ceo who will repeat the hallucination of an LLM as fact and then some guy on the internet will spend days refuting it.

by yubblegum

6/11/2026 at 8:47:49 PM

What an excellent example of Brandolini's law: “ The amount of energy needed to refute bullshit is an order of magnitude bigger than that needed to produce it.”

by Modified3019

6/12/2026 at 8:23:47 AM