USB-C Trigger Board Voltage Roulette

[jjoonathan]

I have been periodically testing USB-C trigger boards and cables because I eagerly anticipate a future with no wall warts, no 5.5mm barrel jacks, no mystery meat voltages and no copy/pasted incorrect barrel jack diagrams.

However, the first generation of USB-C trigger boards all had a huge problem: if the voltage wasn't available or if negotiation failed, they didn't fall back to 0V output (perhaps with a little red light or other hint), they just picked a random lower voltage from the bargain bin and gave it to you. "12V? Eh, best I can do is 9V, enjoy!" Of course, they also frequently put out 5V before they put out the final negotiated voltage, whatever it is. This obviously saves a few cents on a power transistor but it is just as obviously makes the trigger board completely unsuitable for anything not designed specifically to tolerate it. Devices going forward are probably fine, but this behavior makes retrofits a complete non-starter. "Eh," I thought, "most products have glaring issues in their first incarnation, I'll just wait it out." Well, it has been years, the generations of USB-C trigger products have turned over, but the "voltage roulette" behavior seems to not only have survived but still completely dominates the market.

Wtf? Am I using the wrong search terms? Is the world populated entirely by masochists who love debugging surprise brownout issues? What gives?

[jjoonathan]

I'm this close --->||<--- to "fine I'll build it myself," but storing wall warts isn't actually hard enough to justify much effort and I probably shouldn't try to productize this because integrating the functionality into the trigger chip will always win over stapling it on, so it would be a dead end product.

This rant was mostly triggered (groan) by having to allocate a second storage bin to wall-wart storage, which means I now have to evict a more worthy bin to cold storage. So it goes.

[Phil1977]

Many USB-PD interface chips have a "Power Good" status output that - if correctly implemented - exactly tells you that the right voltage was negotiated and is present. If you are not afraid of a low-side-switch then you can just connect an extra FET to this output to switch the load only on if everything is okay.

[thm_w]

Wtf? Am I using the wrong search terms? Is the world populated entirely by masochists who love debugging surprise brownout issues? What gives?

The first thing I would think is label your USB supplies with a max output voltage or get an inline volt display.

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