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Comment by dreamlayers | Hacker News Reader

I find it a bit a bit scary that a microcontroller controls charger voltage. There might be a risk of power glitches or bugs causing output voltages which destroy devices.

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Author here.

Thankfully device-side microchips that interface with USB chargers come with overvoltage protection. For example: http://www.ti.com/lit/ds/symlink/tps65983b.pdf

Devices which charge from wall chargers have to undergo testing for power glitches to obtain FCC certification. I forget the name of the test. Somebody else will know what I'm talking about!

There's a bunch of twilight power conditions in embedded systems that can screw up their function. E.g. brownouts that can lead to partially or fully destroying flash memory in a microprocessor system.

They are usually sporadic and no surge protection test will provide a guarantee against them.

I experienced a brownout a few months ago that destroyed three of my in-wall smart switches. I assume it was the flash memory that got corrupted or destroyed.

This somewhat legendary teardown of an Apple charger is a fun read: http://www.righto.com/2012/05/apple-iphone-charger-teardown-...

Basically, they seem to do a pretty good job isolating high- and low-voltage circuits. As far as I understand it, it is air-gapped, and physically impossible to induce dangerously high voltage on the device side without some mechanical failure that bridges the gap.

a USB pd charger could try to put out 18v to a device that's expecting 5v though, and that can still burn out the device

Assuming reasonable charger design (ie. at least some overcurrent protection) the internal ESD protection of USB-C port in the device that only ever expects 5V (think SRV05-4) should be more than enough to safely trip the overcurrent protection in the charger (or overload it enough that the destroyed component is the charger and not the device).

On the other hand there are documented cases of USB-C PD between two device-ish things (ie. things that can be both power source and sink) failing in variously spectacular ways.

The problem is that the ESD protection can only stop short duration spikes. The device would have to have a fuse (or other overcurrent protection) to prevent the 20V @ 5A as allowed in the USB spec from destroying the ESD circuit.

A USB port should always have a polyfuse. And active disconnect isn't hard either.

Yes, of course. I was thinking of the risk of death and injury, not broken gadgets. Because it is somewhat disconcerting to think how often we/babies touch/stick in our mouth a cable with an almost direct connection to the grid.

I remember there being a guy who reviewed a lot of usb-c cables for compliance (NathanK) having a video on how non-compliant cables can wreck devices:

https://www.youtube.com/watch?v=SjeZB12985c

Maybe that's an example of what you mean?

The spreadsheet by NathanK is here:

https://docs.google.com/spreadsheets/d/1vnpEXfo2HCGADdd9G2x9...

And then there's the Nintendo Switch, a black abyss of USB compliance.

https://switchchargers.com/safety/

I would say the risk is the same as with hardware 'bugs'. Where for example a passive component that drives a power transistor can exceed it's expected tolerance rate. Thats why reliable electronic systems (medical, space, avionics) have some components or circuits redundant.

Some definitely can. There’s a Google Sheet out there listing many different chargers and their levels of compliance. I only remember that Apple did pretty well.

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