3 ms·

To be completely fair, those power banks should have a diode (or some protection circuitry) to prevent their damage. A loose cable could easily put higher volta

by bArray 3y ago

To be completely fair, those power banks should have a diode (or some protection circuitry) to prevent their damage. A loose cable could easily put higher voltage on the port than 5.25V. That said, what an awful USB port to come across. A little reading wouldn't have gone amiss though. My natural reaction would have been to assume it was an output, not an input.

lxgr 3y ago
A diode doesn’t protect from over-voltage; that requires more complicated circuitry as far as I understand. And how would a loose cable cause a voltage spike?
- cjwoodall 3y ago
  TVS diodes can protect from transient voltage spikes when used properly (low impedance to the input connector, properly chosen and with the proper supporting circuitry) Zener diodes can temporarily protect an overvoltage too but you will need something to take all that current that is now going through it, making it pretty hot and likely to fry something You can pair something like this with a positive temperature coefficient thermistor to act as a fuse (as it gets hotter the resistance goes up). These circuits are tricky to tune right, take up space and can add significant cost to a product. So with a drive in consumer products to lower cost smaller things you may not see them everywhere.
- KaiserPro 3y ago
  perhaps a they meant a zener diode, which can be used to clamp a voltage? The downside being that it dissipates the excess energy across it's self. > how would a loose cable cause a voltage spike? From the top of my flu-y head, connecting and disconnecting an inductive load (like a motor) can cause spikes. However in USB land, that's pretty rare. dc-dc step up devices use an oscillator to charge and discharge an inductor to achieve a certain voltage increase. They _could_ be noisy when starting up, or have transient load.
  - bArray 3y ago
    > perhaps a they meant a zener diode, which can be used to clamp a voltage? The downside being that it dissipates the excess energy across it's self. Maybe in conjunction with a self-reset polyfuse - buys just enough time to trip the fuse. > From the top of my flu-y head, connecting and disconnecting an inductive load (like a motor) can cause spikes. However in USB land, that's pretty rare. Exactly - and it's not all that rare. A USB fan, a spinning disk drive, etc. In the right condition even a capacitor can be a problem (difficult to simulate, but it can become a short-term battery cell).

by bArray 3y ago

lxgr 3y ago

A diode doesn’t protect from over-voltage; that requires more complicated circuitry as far as I understand. And how would a loose cable cause a voltage spike?

cjwoodall 3y ago
TVS diodes can protect from transient voltage spikes when used properly (low impedance to the input connector, properly chosen and with the proper supporting circuitry) Zener diodes can temporarily protect an overvoltage too but you will need something to take all that current that is now going through it, making it pretty hot and likely to fry something You can pair something like this with a positive temperature coefficient thermistor to act as a fuse (as it gets hotter the resistance goes up). These circuits are tricky to tune right, take up space and can add significant cost to a product. So with a drive in consumer products to lower cost smaller things you may not see them everywhere.
KaiserPro 3y ago
perhaps a they meant a zener diode, which can be used to clamp a voltage? The downside being that it dissipates the excess energy across it's self. > how would a loose cable cause a voltage spike? From the top of my flu-y head, connecting and disconnecting an inductive load (like a motor) can cause spikes. However in USB land, that's pretty rare. dc-dc step up devices use an oscillator to charge and discharge an inductor to achieve a certain voltage increase. They _could_ be noisy when starting up, or have transient load.
- bArray 3y ago
  > perhaps a they meant a zener diode, which can be used to clamp a voltage? The downside being that it dissipates the excess energy across it's self. Maybe in conjunction with a self-reset polyfuse - buys just enough time to trip the fuse. > From the top of my flu-y head, connecting and disconnecting an inductive load (like a motor) can cause spikes. However in USB land, that's pretty rare. Exactly - and it's not all that rare. A USB fan, a spinning disk drive, etc. In the right condition even a capacitor can be a problem (difficult to simulate, but it can become a short-term battery cell).