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I have 4-port SS PCIe card, which outputs 5V 900mA on each USB port.

I have a need to communicate with a distant USB device and the cable length and current demands are probably dropping the available voltage below specification at the device end.

What modifications need to be done on the card to crank up output voltage?

  • No information yet on considering using larger conductor cross section cabling to minimise the volt drops.
  • USB maximum cable lengths are also limited by signal propagation delays and capacitive signal degradation.
  • The USB ports will obviously become dangerous for normal devices due to over voltage supply.
  • There is no comparison with other cards such as this one that can supply 2A per port and may not suffer from supply voltage droop as much under load.
KalleMP
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Zubaer Halim
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    Why would you even ask such a question? Do you want to fry some USB devices? – Eugene Sh. Sep 15 '17 at 17:22
  • No. To be precise, do you know any chip level modification that can be done to crank up the voltage? Cause the USB cable is ridiculously long, and voltage drops below required level at the end of the USB cable. – Zubaer Halim Sep 15 '17 at 17:31
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    Then use a USB repeater. Your proposed "solution" is the worst thing you could think of. – Eugene Sh. Sep 15 '17 at 17:32
  • Powered hub on the target end? – pjc50 Sep 15 '17 at 17:36
  • You would have to see investigate the power supply circuits for the USB ports. There is a vanishingly small chance that the circuitry could be hacked to up the voltage by 0.5V or whatever but the communications circuitry might complain if the supply is shared. I vote for a out of specification (over voltage) USB driver type device (single port powered hub) at the local end if you do not have power at the remote end. – KalleMP Sep 15 '17 at 21:23

2 Answers2

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Unless the PC card and peripheral device both support the Power Delivery specifications, there is not much one can do on the card to achieve higher power delivery modes. And definitely not with the Type-A ports as in the referenced card. You can't just crank-up the voltage, you need an intelligent system that negotiates higher voltage and currents on both ends of USB 3.1 link partners.

What can be done however is to have (or design and build) an adapter that provides the variable power (from likely external source) in compliance to Power Delivery specifications. The adapter should include a dedicated circuitry that provides PD communication, and must convert the original Type-A to Type-C port (because the PD works only over CC lines, and VBUS protocol was abandoned). Obviously your peripheral device should understand this protocol and respond accordingly. However, I wasn't able to find this kind of devices on the market, only some HDMI adapters with side function of power delivery.

If your suffer a simple voltage drop along long cables and want to compensate it, the solution is either to use self-powered devices, or use a self-powered (via Ac-DC adapter) hub on the side of peripheral device (if the device can't be self powered).

As a last resort, if you have this PC card and can get it's schematics (or reverse engineer it), and determine that VBUS power supply (+5V) has a voltage regulator of adjustable type, you can beef-up the VBUS to 5.5V by changing corresponding resistor dividers. But without details of your particular PC card, no advice can be rendered.

Ale..chenski
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Most likely whatever voltage you deliver to the 5V pin on the power input connector of that card will be delivered to the sockets on the back.

So you could build a power unit (or get one of the cheap adjustable switchmode converters from ebay and adjust it) that delivers slightly over 5V to that pin and most likely it will result in a higher voltage delivered to the sockets on the back. The problem is if you go too high you risk frying stuff and exactly how high is too high is something it's difficult to be sure of.

Peter Green
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