mr. h

It's a shame you didn't get this article checked by someone who actually knows anything about power electronics. It's really quite confused in multiple ways.

Firstly, it refers to GaN "chips" implying that it's being used here for integrated electronics (i.e. a single die containing multiple transistors, like a microprocessor), but that's not what's happening. These chargers are using established switched-mode power converter topologies and replacing silicon (Si) MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors, a Si die consisting of a single transistor, that is able to handle lots of voltage and current, relative to a microprocessor transistor) with GaN HEMTs (High-Electron-Mobility Transistors).

Secondly, it refers to voltage being "conducted". Power transistors do not "conduct" voltage. In power converters like these, the power transistors operate in a "switched mode", being either "off", or "fully" on (where they behave like a very small resistance in the tens of milliohms range). When "on", they conduct current, and when "off" they block voltage.

When conducting, the power transistor dissipates some power (referred to as "conduction loss"), this being equal to the current squared multiplied by the resistance. So, lower resistance = lower losses. However, when making the transistor, there is a tradeoff between how many volts the transistor can block when off, and how low its resistance is. The more volts you need to block (in the case of these power converters, the transistors are usually rated at around 600 V to 650 V), the higher the resistance. The wide bandgap of GaN gives a better tradeoff between voltage blocking capability and on-resistance, compared to Si. Additionally, when transitioning from "on" to "off" or visa-versa, there is a brief period of very high power dissipation in the transistor (referred to as "switching loss"). Crudely speaking, the faster a transistor can perform these transitions, the lower the switching loss will be. GaN power transistors are much faster than Si devices and the switching losses are much smaller.

At a very basic level, switching power converters operate by taking small packets of energy from the source (in this case a mains/grid connection), storing that energy temporarily, and then outputting that energy to the load. The energy is stored internally in inductors and capacitors, and routed/transferred with power transistors and transformers. How often the packets of energy are routed around is referred to as the switching frequency. The higher the switching frequency, the smaller the energy storage components and transformers can be. However, as mentioned previously, each time a transistor transitions from "on" to "off" or visa versa, it wastes some energy as heat. So the higher the switching frequency, the higher the losses. If in each transition you lose less heat, you can afford to increase the switching frequency and therefore make the inductors, capacitors, and transformers in your power converter smaller.

In summary, the key benefits of GaN over Si, when it comes to power transistors, are:

A better tradeoff between on-state resistance and blocking voltage (lower conduction loss)
Much faster switching transitions leading to lower switching losses, allowing a higher switching frequency.

Now, both GaN and Si transistors have an upper limit of temperature that they can safely operate at, typically 150 C or 175 C. Any power dissipation in the transistor is converted to heat, which must be extracted by a cooling system to keep the transistor below the maximum allowed limit. If you've less heat to extract (due to lower losses), you can make the cooling system smaller. So, there's two ways that the power converter can be made smaller:

1. Get the losses down so the cooling system can shrink
2. Increase the switching frequency to make the inductors, capacitors, and transformers smaller

When compared to power converters using Si transistors, a GaN-based one will be using a mixture of these two approaches.

GaN transistors are also smaller than Si ones, but the impact of that is fairly minimal relative to the other effects outlined above.

To learn more, you can get a free book on power electronics here (registration is required, but free). For the avoidance of doubt, I am not Barry Williams.

The whiners who are trying to argue the case for an xMac do themselves a great disservice by poo-pooing the new Mac Pro. It makes you look like you are unable to process information logically and makes it more likely that people will just dismiss everything you have to say.

I do think that there is a very good case for the xMac, but there's no need to rubbish the Mac Pro in order to make said case. The new Mac Pro is a seriously awesome and absolutely gorgeous machine, as is the XDR display, and despite the fact I'm nowhere near the target market for these things, it still made me almost giddy with excitement when it was announced - and it's been a long time since any hardware announcement from Apple had me so excited. It was just so refreshing to see Apple take this stuff seriously and produce a correspondingly uncompromised product. The Mac Pro is expensive. But it is also good value. And as for the XDR display, that is just astonishingly good value - come on, this thing is better in every way than a monitor costing $40+k, and it costs $6k - if that's not staggeringly good value, I don't know what is. 

Now, having said all that, there does still remain the question - why on earth is Apple making the entry cost for a configurable machine on the macOS platform $6000??? It's like they actively don't want to sell more Macs! It's a decision that just baffles me. You can't seriously tell me that Apple offering an xMac that starts at $999 is going to cannibalise a $6000+ workstation? They are completely different products for completely different markets and there is simply no way that someone who would consider buying a $6k workstation would end up buying a $1k tower instead, and equally and just as importantly, visa versa. Here is what I would envisage an xMac consisting of:

A tower design with easy access to innards, but something much simpler and less high-end than the new Mac Pro
Support for intel Core i3, i5, i7, i9 desktop processors
Support for up to 64 GB RAM (in DIMM Slots)
NVMe SSD (user upgradeable)
two PCIe slots
dedicated graphics options (but not supporting anything like the MPX Modules for Mac Pro).

And what would the $999 option consist of? Take the $799 mini and put those specs in a tower:

• 3.6GHz quad-core 8th-generation Intel Core i3 processor
• 8GB 2666MHz DDR4 memory
• Intel UHD Graphics 630
• 128GB SSD

This configuration would have both PCIe slots empty. Adding a dedicated graphics card would enable macOS dynamic graphics switching.

BTW - just looked at the Mac Mini, and Apple's prices for storage and RAM are quite simply disgusting and totally unjustifiable. So that's the reason they don't have an xMac.

Rayz2016 said:

Agreed. It’s a personal device with limited storage. 

iPad Pro max storage = 1 TB.

And the MacBook Air base configuration is still only 128 GB. Should Apple disable multi-user support in macOS running on the MacBook Air?

StrangeDays said:

mr. h said:

entropys said:

The only thing could be multiuser support for ipadOS. It’s in TVOS though.

When watching the keynote I got all excited that multi-user support in tvOS might carry over to iPadOS, but no. It's a very disappointing and cynical move by Apple to leave this feature out of iPadOS.

No, it’s not cynical or conspiratory. … iPads are personal devices

iPads are only personal devices because Apple cynically forces them to be so. The technical issues to which you allude are not a problem; they have been well solved for over a decade in macOS. iPad is available with up to 128 GB storage, and iPad Pro is available with up to 1 TB, and the "large apps" would only take up one lot of storage space anyway; it'd only be personal files and preferences that are user-specific (see macOS). Oh yeah, and they've also already done most/all of the work with "Shared iPad" for education.

It would be easy for Apple to make iPad OS multi-user, but Apple doesn't want to do that because then you'd get people making their kids share an iPad instead of buying them one each. Admittedly I do that already but I'm teetering on the edge of buying a second one. So Apple's policy of refusing multi-user support in iPad OS may achieve its aim of selling more iPads, but I will continue to view that as a cynical consumer-unfriendly policy.

entropys said:

The only thing could be multiuser support for ipadOS. It’s in TVOS though.

When watching the keynote I got all excited that multi-user support in tvOS might carry over to iPadOS, but no. It's a very disappointing and cynical move by Apple to leave this feature out of iPadOS.

Changing the subject...

In macOS, when Dark Mode is enabled, you can set some apps to still display in "light mode", for example Maps, and messages in Mail. Can you do the same thing in iOS 13?