7 ms·

> That would force all power adapters to support a fixed maximum current, which in many cases would mean either wasted materials (consider e.g. shipping a 100W

by ilyt 3y ago

> That would force all power adapters to support a fixed maximum current, which in many cases would mean either wasted materials (consider e.g. shipping a 100W adapter with a smartphone) or unsafe conditions (with a device attempting to pull 5A from an adapter supporting only much less than that). No, it would not require any of that. It would require only for cable to signal it's max current capacity. So cheap cable would allow for say 20v/0.5A (10W), while decent one could signal 2A(40W) or max. Simplest way of signal would be as the previous USB buses used, via a specified value resistor on one of the pins. More complex would be signalling the power supply power to the device on the other side, especially if you want dynamic power or reversible charging direction. But USB-PD is generally horrifically complicated for what it does

lxgr 3y ago
> It would require only for cable to signal it's max current capacity. As you say yourself a bit later, you'd need at least two "simple" resistors (one for the cable itself, one for the adapter) – otherwise it's only fixed-cable power supplies (and I really, really hate having to throw away an entire high-quality power supply just because the cable frayed at the laptop end). > But USB-PD is generally horrifically complicated for what it does Which parts would you suggest are safe to omit, in a world where you want to be able to charge both small accessories (Bluetooth headphones etc.), smartphones, and large laptops using a single connector?
- ilyt 3y ago
  > As you say yourself a bit later, you'd need at least two "simple" resistors (one for the cable itself, one for the adapter) – otherwise it's only fixed-cable power supplies (and I really, really hate having to throw away an entire high-quality power supply just because the cable frayed at the laptop end). You could have end device regulate itself by looking at voltage drop, akin to MPPT. And note that simple (sub-10W) devices could opt to implement nothing whatsoever and just get the minimum 20V/0.5A, making small accessories need nothing whatsoever when it comes to extra chips to handle it. You really need communication only when you start needing features like switchable sink/source function or voluntarily lowering power usage. >>But USB-PD is generally horrifically complicated for what it does > Which parts would you suggest are safe to omit, in a world where you want to be able to charge both small accessories (Bluetooth headphones etc.), smartphones, and large laptops using a single connector? Not talking about featureset but how hideously complex the implementation is. I remember some early adopters tried to implement it using a microcontroller and it ate like 30+kB of code and it was more than half of total product's code The spec (3.0, rev 1.1) is 574 pages. No fucking wonder we have so many devices implementing it subtly wrong. Hell, they even decided "no, none of the existing serial protocols fits our super special use case, need to invent that too. At least they didn't reinvent CRC32...
  - eternityforest 3y ago
    I don't understand the implementation, it's pretty nuts. And the multiple layers of optional features and fragmentation are pretty awful. I kinda wish they hadn't specified any power levels other than 5v and full programmable PPS.... I also wish they had implemented a dedicated solar profile to simplify solar generators, so a panel could say "I will act like a current source and do MPPT". They probably could have done Dallas One Wire for the signalling and been just fine. It could also be how the cable chip communicates, and very small simple devices could use it without the full USB stack. But, I can accept it just because of how well it works in practice as is.

by ilyt 3y ago

lxgr 3y ago

> It would require only for cable to signal it's max current capacity. As you say yourself a bit later, you'd need at least two "simple" resistors (one for the cable itself, one for the adapter) – otherwise it's only fixed-cable power supplies (and I really, really hate having to throw away an entire high-quality power supply just because the cable frayed at the laptop end). > But USB-PD is generally horrifically complicated for what it does Which parts would you suggest are safe to omit, in a world where you want to be able to charge both small accessories (Bluetooth headphones etc.), smartphones, and large laptops using a single connector?

ilyt 3y ago
> As you say yourself a bit later, you'd need at least two "simple" resistors (one for the cable itself, one for the adapter) – otherwise it's only fixed-cable power supplies (and I really, really hate having to throw away an entire high-quality power supply just because the cable frayed at the laptop end). You could have end device regulate itself by looking at voltage drop, akin to MPPT. And note that simple (sub-10W) devices could opt to implement nothing whatsoever and just get the minimum 20V/0.5A, making small accessories need nothing whatsoever when it comes to extra chips to handle it. You really need communication only when you start needing features like switchable sink/source function or voluntarily lowering power usage. >>But USB-PD is generally horrifically complicated for what it does > Which parts would you suggest are safe to omit, in a world where you want to be able to charge both small accessories (Bluetooth headphones etc.), smartphones, and large laptops using a single connector? Not talking about featureset but how hideously complex the implementation is. I remember some early adopters tried to implement it using a microcontroller and it ate like 30+kB of code and it was more than half of total product's code The spec (3.0, rev 1.1) is 574 pages. No fucking wonder we have so many devices implementing it subtly wrong. Hell, they even decided "no, none of the existing serial protocols fits our super special use case, need to invent that too. At least they didn't reinvent CRC32...
- eternityforest 3y ago
  I don't understand the implementation, it's pretty nuts. And the multiple layers of optional features and fragmentation are pretty awful. I kinda wish they hadn't specified any power levels other than 5v and full programmable PPS.... I also wish they had implemented a dedicated solar profile to simplify solar generators, so a panel could say "I will act like a current source and do MPPT". They probably could have done Dallas One Wire for the signalling and been just fine. It could also be how the cable chip communicates, and very small simple devices could use it without the full USB stack. But, I can accept it just because of how well it works in practice as is.