3 ms·
>Smartphones already do this. They essentially measure the resistance of the cable by measuring the voltage and correlating it with the current drawn, and regul
by shadowpho 1y ago
>Smartphones already do this. They essentially measure the resistance of the cable by measuring the voltage and correlating it with the current drawn, and regulate the current accordingly.
No! Where did you hear this?
Smartphones usually either rely on type-c pd nowadays or do far less standard Samsung/Apple resistor on usb line check.
Some power banks also do terrible thing where they increase current pull until they see voltage starting to collapse but that’s to check for OC limits on load switch. However that’s really starting to go away because type c just works
- lxgr 1y ago> Some power banks also do terrible thing where they increase current pull until they see voltage starting to collapse If I’m not mistaken, that was explicitly allowed under USB Battery Charging. But chargers have to opt in to that via signaling on D+/D-.
- userbinator 1y agoIt's been common for many years. Look for a document titled "Mediatek Pump Express Introduction". Another useful phrase to search for more information: "cable impedance detection". Apparently several patents on it too.
- shadowpho 1y ago>Mediatek Pump Express Introduction Yep read it. It does even more terrible things (modulating current to change voltage), but no monitoring for voltage drops. It’s also rarely supported, and looks like they just switched to pd3 (the sane protocol)
- userbinator 1y agobut no monitoring for voltage drops Did you not see: "Do cable imp. Calculation. Protect cable from burnout" on page 12 "Adjust Vbus according to cable impedance/quality" on page 14 and "Cable Impedance Measurement" on page 15? Pump Express is their fast charging protocol, but even before that, in the days of feature phones, they were already doing the measurements and adjusting charging current.