Remember the “good old days?” 1993, to be precise. Yes, we know that 1993 was the year of NAFTA and “Robin Hood: Men In Tights,” but that year also notched up several technological firsts: the first Pentium microprocessor; the birth of the World Wide Web at CERN; and the launch of IBM’s Simon Personal Digital Assistant, the world’s first smartphone.
It cost $899 and had a battery life of just one hour. Some would say we haven’t progressed much in the last two decades. Although its per-dollar performance has improved dramatically since 1993, the price for a top-end smartphone hasn’t seen a whole lot of change. And short battery life is still the biggest complaint of consumers.
One feature that has changed is the charging method. Back in good old days, mobile phones had power plugs and dedicated chargers. Now almost all phones charge use the power pin of their USB port.
For a given charging current, the charging time of a battery is approximately proportional to its capacity. Over the last decade, smartphone manufacturers have steadily increased battery size (Fig. 2). All things being equal, a USB port will take twice as long to charge a Galaxy S8 as it will to charge an S1.
As the power and data requirements increased for USB-connected devices, the USB specification has tried to keep pace. The data rate has gone from 480 Mb/s (USB 2.0) to 10Gb/s (USB 3.1). The table shows the increase in maximum power for successive USB revisions.