5 ms·
The failure modes are completely different. The MacBook went overcurrent when a bad cable told an attached phone it could draw more current than it should. Dete
by smbarber 11y ago
The failure modes are completely different. The MacBook went overcurrent when a bad cable told an attached phone it could draw more current than it should. Detecting overcurrent due to a badly behaved device or a short in the cable is fairly common.
The cable attached to the Chromebook was totally miswired and flipped Vbus and ground, supplying -5V where 5V was expected. As the article said, nothing is really designed to handle this kind of failure because it should be blatantly obvious to the cable manufacturer if there were any sort of quality control.
- X-Cubed 11y agoThat's not entirely true. Reverse polarity protection is very common, and often only requires a single diode in series with the +V line, so that current can only flow in one direction.
- marshray 11y agoA diode will drop about 0.5-0.6 volts, which could eat 10% of your energy, so reverse polarity protection is usually used in devices where someone could plausibly install the batteries backwards. I think it's probably rare on something on a highly controlled standard connector like USB.
- rrmm 11y agoIt's fairly easy to do it without the diode drop if you use a mosfet, but you do incur the cost of a more expensive part.
- yardie 11y agoIt's usually common in low voltage, low current devices. I have a massive inverter charger on our boat that has in giant letters "NO REVERSE POLARITY PROTECTION". It typically handles up to 200amps at 12V.