I would like to make a USB dongle. According to USB 2.0 spec, max 500mA can be driven from one device. But I am afraid it may not be enough. I have seen some USB hard disk using a dual head USB cable to double the power supply. I would like to know if anyone has detailed spec of the cable. Does it mean 1000mA will be supplied? And what the dual head USB cable doing actually? It just connects the power pins of two ports together? Thank you so much.
What i believed these days is that, if you use a dual connector USB, your PC motherboard will not get loaded. otherwise, it max. current from the single USB port, so over the time the chances of USB port failure is more due to excess power drawn for long period.