Everybody always talks about the massive computing power of smartphones (movies love the moon mission comparison) but still my phone rarely gets hot. (Only when I use it while charging sometimes)
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I also wanted to mention that there are “gaming” phones out there that do have built-in fans that can be very audible. I have the REDMAGIC 7S Pro myself and while both charging or playing a CPU intensive game, those fans will kick on and light up the fancy exhaust port on the side where the air escapes.
The phone will switch between performance states to never cross certain thermal thresholds both to protect the user and the battery, think of your phone as a performance free diver skilled at holding breath, while larger active cooling computers will have some functional breathing apparatus like a snorkeler or a diving bell, and when you get into liquid cooling you are more like submarines or just scuba divers. Charging will be the greatest thermal load especially if you are using a fast charging system, especially the top 20% of your batterys charge.
At the core the reason smartphones don’t need fans is because majority use ARM based processors which are more efficient in terms of power. ARM makes use of a small instruction set that’s highly optimized. Because it’s a smaller instruction set, it requires less transistors, which results in less wattage/power.
Instruction sets are the commands that essentially tells your CPU what to do. The problem with Intel processors is that they have backwards compatibility with x86 (32-bit) for x64(64-bit), which adds more instructions, which leads to more transistors and that leads to a higher power/wattage.
Going back to using less power, heat is generally produced by more wattage/power going through the device. Wattage/power is voltage*amps, so increasing either will raise wattage. On desktops, they use 12V rails for powering the GPU and CPU. If you look up specs on a computer’s CPU you’ll notice TDP ratings that can go well over 100W. The RTX 2060 if I recall, has 160W TDP rating, 160/12 = ~13 amps.
Meanwhile, most smart phones operate from ~3.2V (discharged) to 4.2-4.5V (charged), there are also some series battery phones that operate between 6.4V-9V. Most phones last most of the day while using them, it’s safe to say that amperage is below 1A for most cases.
One thing to also mention is that just because they don’t use fans, doesn’t mean they don’t use anything to dissipate the heat. Several phones have heat sinks and in some cases the casing of the phone also dissipates the heat.
They use a lower power cpu type called ARM which also saves on battery. Arm chips have improved rapidly due to the popularity of phones, and are feasible as a replacement for x86 (“typical” computer cpu’s)
Smartphones have massive computing power compared to moon missions, and weak computing power compared to laptops.
And they do get hot sometimes, like when playing certain games.
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