It appears to me that the currently available Expansion Cards for USB-A and USB-C do not include any galvanic isolation between the Laptop and any connected Device. Is that assumption true? If so, are there any plans to make versions with galvanic isolation in the (near) future? This would allow the Framework Laptop to be used in High Voltage applications and provide a protection against electric shock both for the user and the Laptop itself.
Just thinking out loud, because the case is metal, I’m not sure you can get enough isolation even if you had the right circuit. Unless you filled the module with epoxy…?
I guess I’m not familiar with the actual use case. I’m used to thinking about isolated USB for stuff like ground loops and interference. Could you explain a bit what your use case is?
That said, DIgiKey has a bit of a how-to article, https://www.digikey.com/en/articles/techniques-and-solutions-for-usb-power-and-data-isolation, and it looks straightforward enough. The ADUM6140 featured near the bottom does USB Full Speed (12 Mbps, which seems to be the fastest you can isolate), and it’s a bit big but I think it could be squeezed into a card, if all other problems could be solved. I think their recommended isolation transformer could be fit in, too.
Oh, I stand corrected, 480 Mbps versions are out, and there’s a Japanese firm that has a USB 3.0 5 Gbps isolator.
I like your thoughts so far, I have some additional comments about what you said. The case from the Ethernet card is plastic, so an isolated card could also be made out of plastic. Filling with epoxy would be possible in my opinion, this would reduce repairability, but a repair would likely void any certification anyway. One could argue in the same way that a longer card would more than make up for the benefit provided. I believe it would also help to distinguish the isolated version from the normal one, would not want to accidentally use the not isolated one.
My specific use case is for programming microcontrollers that are on an isolated level to earth in high voltage systems, in case of system failures the connection ground could be raised to the maximum system voltage. With the normal cards, this could lead to the Laptop being exposed to the high voltage and to the Laptop chassis being also connected to this voltage, touching the chassis (i.e., using the laptop) would now close an electric circuit.
There are of course other safety measures that would prevent this worst case, like removing the Microprocessor from the system, but we all know that someone will be too lazy.
I hopefully don’t have to explain why having a high voltage flowing through the human body is a bad situation.
1 Like
Already got a prototype going for USB-A. One thing to note is that according to my isolation calculations between pad to pad you will get about 1.2kV of isolation along with breakdown of the FR4 at these voltages. My first prototype was a USB1 speed one, my new version works at 12MB/s now, but I implemented a small switch as if you were using a mouse/keyboard at USB1 speeds with the 12MB/s mode it would not work. The issue being is the switch is only isolated to 250 or 500volts AC RMS, meaning it’s quite hard to just be a standard universal isolator.
1 Like
That’s pretty cool speaking as someone who made a mistake with a prototype on a breadboard and sent 120v through USB about a decade ago. Since then I use an optoisolator circuit when designing.
Fortunately that was when I could use cheap 200-300 dollar machines.
Today I would probably want to use an external COTS module since they probably tested it more thoroughly, and probably have a procedure for reimbursing destroyed equipment if the device is found faulty.
This is still really cool if working in an environment where there could be an unexpected “oops” especially if this is your own machine.