1. Stop power from back feeding after the computer is turned off.
2. Allow tapping the USB’s 5V signal for enabling the ACPPS without cutting a USB cable open.
3. Allow the USB port to be used to enable the ACPPS and still be a functioning USB port.
4. Power a USB hub using only the USB cable.

1. In a normal scenario, the computer ‘feeds’ power to the hub. ‘Back feeding’ is the opposite, the hub ‘feeds’ the PC, which it shouldn’t do. If power ‘back feeds’ the ACPPS will stay on after the computer turns off.  In a round about way, the ACPPS 5V output gets tied to the enable signal and it gets stuck in a loop. The ACPPS stays enabled until you disconnect a wire that is part of the loop. That’s where the isolator description comes in. The USBi stops power ‘back feeding’ into the computer with the use of a diode. (Orange arrow)

2. In many Car-PC applications the computer has a limited number of USB ports. Sacrificing a USB port solely to trigger the ACPPS doesn’t make sense. One option is to cut the USB cable open and extract the 5V signal to enable the ACPPS. The USBi does exactly this without cutting the cable open. (Blue arrow)

3. Some powered USB hubs won't turn on if the 5V signal is missing from the USB cable. The isolator allows power on the 5V wire to continue (Green arrow) so that the hub turns on. The diode used in the USBi is a Schottky diode, known for low voltage drop and quick response time. I have run several USB speed tests using flash drives connected through the USBi and saw no impact on performance or operation.

4. The USBI is capable of providing power from the ACPPS to the HUB without using a dedicated power cable. A buss powered hub is limited by the amount of current the computer supplies to it. USB ports have current limiting circuitry set at 0.5A. When more than 0.5A is used, the port will shut off and all attached devices will disconnect. In buss powered mode, a hub is limited to 0.5A to power itself and all attached devices. Using the USBi, the 5V output of the ACCPS can be connected to the device side of the diode, allowing the USB cable to carry more than the 0.5A. (Red arrow) A hub could act like an externally powered hub, wile in buss powered mode, because it is receiving power from the ACPPS instead of the current limited USB port of the computer. This use of this capability is AT YOUR OWN RISK. USB cables and connectors are only designed for 1A. Exceeding this may cause the cable to burn up, possibly damaging your equiptment or turning your ride into a car-b-que!