Comment by JKCalhoun
3 days ago
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.
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.
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.
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.
2 replies →
> 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)
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.