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Could someone ELI5 what makes GaN PSUs/chargers more efficient than earlier technologies?

by aix1 4y ago

diffeomorphism 4y ago
It is not so much about efficency but about size. Galliumnitride generates less heat than silicon, so you can make much smaller power supplies.
- Doxin 4y ago
  If I recall correctly GaN transistors also just generally are better in a lot of metrics. Faster switch times, Lower resistance, Higher permissible voltages, etc. It really does look like a miracle technology.
  - rowanG077 4y ago
    Are they good for logic (CPUs, GPUs etc) as well or just for power applications?
    - namibj 4y ago
      In theory, but they are hard to miniaturize for logic ICs.
    - kf7njh 4y ago
      I would argue probably not. GaN has a higher bandgap voltage (3eV iirc... 1eV for Silicon), which means a CPU would need to be run at a higher voltage. As a quick rule of thumb for huge transistor count ICs: Power (heat) = freq*Voltage^2 I won't go into detail, but you can see how for a CPU designer decreasing voltage is critical to increasing speed. Remember a decade ago when CPUs were like 1.2V and we hit this ~3GHz "wall"? But now due to breakthroughs in process nodes, CPUs are running I think ~0.8V but boosting up to 5GHz. If we make the same CPU on a GaN process, the transistors would probably need ~3V to switch, and thus need to be run about 9x slower to meet the same package power (or I guess you could run it at the same speed but then try and figure out how to cool a 9x higher TDP CPU). Furthermore, GaN is difficult to manufacture into a monocrystaline perfect lattice compared to Silicon. You can image that for modern 7nm/5nm nodes, where there are sometimes angstroms of distance in a transistor, having a foundation full of defects can be devastating to the yield. Power electronics is a totally different domain with different challenges. In this area GaN excels, but for ICs I don't think it makes sense. Let's see in 20 years though. GaN is relatively new compared to Silicon and might just need some further refinement. Just my 2c though. Someone correct me if I'm wrong.
      - Doxin 4y ago
        On the other hand GaN is much more tolerant of hight temperatures than regular resistors, so who knows which way the balance would fall? Of course GaN is a much newer technology too so I imagine it'd have some serious catching up to do before it gets to the scales where it'd be useful for CPUs.
- yetanotherloser 4y ago
  Converting less of the switched energy to heat IS efficiency; there's no difference.
pjc50 4y ago
The scientific answer appears to be "high Johnson's figure of Merit", for which the primary source is a 1965 journal: https://worldradiohistory.com/hd2/IDX-Site-Technical/Company-Pubications/Radiotronics/IDX/Radiotronics-1966-01-OCR-Page-0002.pdf https://worldradiohistory.com/hd2/IDX-Site-Technical/Company... (you can go forwards by editing the URL) There are two factors: - you need a high breakdown voltage, so that for a given voltage you want to switch you can make the transistor channel as short as possible; shorten the physical distance that charge carriers have to flow in the semiconductor. - you need a high maximum drift velocity, which governs the rate at which charge carriers can flow through the semiconductor Those contribute to reducing the on-resistance of the transistor, thereby decreasing its heat output for a given size.

Could someone ELI5 what makes GaN PSUs/chargers more efficient than earlier technologies?

by aix1 4y ago

Could someone ELI5 what makes GaN PSUs/chargers more efficient than earlier technologies?

It is not so much about efficency but about size. Galliumnitride generates less heat than silicon, so you can make much smaller power supplies.

Doxin 4y ago
If I recall correctly GaN transistors also just generally are better in a lot of metrics. Faster switch times, Lower resistance, Higher permissible voltages, etc. It really does look like a miracle technology.
- rowanG077 4y ago
  Are they good for logic (CPUs, GPUs etc) as well or just for power applications?
  - namibj 4y ago
    In theory, but they are hard to miniaturize for logic ICs.
  - kf7njh 4y ago
    I would argue probably not. GaN has a higher bandgap voltage (3eV iirc... 1eV for Silicon), which means a CPU would need to be run at a higher voltage. As a quick rule of thumb for huge transistor count ICs: Power (heat) = freq*Voltage^2 I won't go into detail, but you can see how for a CPU designer decreasing voltage is critical to increasing speed. Remember a decade ago when CPUs were like 1.2V and we hit this ~3GHz "wall"? But now due to breakthroughs in process nodes, CPUs are running I think ~0.8V but boosting up to 5GHz. If we make the same CPU on a GaN process, the transistors would probably need ~3V to switch, and thus need to be run about 9x slower to meet the same package power (or I guess you could run it at the same speed but then try and figure out how to cool a 9x higher TDP CPU). Furthermore, GaN is difficult to manufacture into a monocrystaline perfect lattice compared to Silicon. You can image that for modern 7nm/5nm nodes, where there are sometimes angstroms of distance in a transistor, having a foundation full of defects can be devastating to the yield. Power electronics is a totally different domain with different challenges. In this area GaN excels, but for ICs I don't think it makes sense. Let's see in 20 years though. GaN is relatively new compared to Silicon and might just need some further refinement. Just my 2c though. Someone correct me if I'm wrong.
    - Doxin 4y ago
      On the other hand GaN is much more tolerant of hight temperatures than regular resistors, so who knows which way the balance would fall? Of course GaN is a much newer technology too so I imagine it'd have some serious catching up to do before it gets to the scales where it'd be useful for CPUs.
yetanotherloser 4y ago
Converting less of the switched energy to heat IS efficiency; there's no difference.

pjc50 4y ago

The scientific answer appears to be "high Johnson's figure of Merit", for which the primary source is a 1965 journal: https://worldradiohistory.com/hd2/IDX-Site-Technical/Company-Pubications/Radiotronics/IDX/Radiotronics-1966-01-OCR-Page-0002.pdf https://worldradiohistory.com/hd2/IDX-Site-Technical/Company... (you can go forwards by editing the URL) There are two factors: - you need a high breakdown voltage, so that for a given voltage you want to switch you can make the transistor channel as short as possible; shorten the physical distance that charge carriers have to flow in the semiconductor. - you need a high maximum drift velocity, which governs the rate at which charge carriers can flow through the semiconductor Those contribute to reducing the on-resistance of the transistor, thereby decreasing its heat output for a given size.