For smartphones and compact notebooks, power supply via USB-C is now standard: The twist-proof connector can deliver up to 100 watts – provided a correspondingly thick power supply unit. For high-performance notebooks with rapid 3D graphics chips, this maximum specified in the standard was not sufficient, which led to a proliferation: with such notebooks, classic round plugs are again common, which cannot be exchanged between notebooks from different manufacturers. Dell, in turn, has expanded the standard proprietary to 130 watts, which then only works for the combination of certain in-house notebooks and power supply.
The USB-IF (Universal Serial Bus Implementers Forum) standardization committee has taken on the matter: In the future, charging power of up to 240 watts will be possible. Apart from a few desktop replacement systems, this is enough for the mass of gaming notebooks and opens up new possibilities for supplying power to other device classes.
The expansion from 100 to 240 watts made new revisions of two specifications necessary: The “USB Type-C Cable and Connector Specification”, which defines the electrical parameters of plugs, sockets and cables, was raised to revision 2.1 and the “USB Power Delivery” Specification “with the protocol details is available in revision 3.1. The double was necessary because new EPR voltage levels (Extended Power Range) are being defined, which has broader effects.
So far, USB-C stopped at 20 volts. With the EPR extension, 24 volts, 36 volts and 48 volts are now also possible. Up to 5 amps are still allowed to flow in all stages – an important difference to Dell’s proprietary 130-watt extension mentioned above, which provides 6.5 amps at 20 volts. The stronger EPR levels mean that USB-C cables are not thicker (and therefore stiffer) than they already are.
However, adjustments are necessary: other capacitors are required in the plugs so that when the voltage is removed, no arcing occurs, which would inevitably damage the contacts. Analogous to USB-C cables, which are approved for 5 amps, EPR cables have a corresponding electronic marking that shows them to be able to withstand up to 50 volts. Without such a marking, a maximum of 3 amps will flow in the previous mode, which is now called SPR (Standard Power Range). Since the human eye can only read electronic markings with difficulty, EPR cables should also have a corresponding visible mark.
New processes have been defined at the protocol level. There was already communication between the partners in the well-known SPR mode: A source had to tell a sink which modes it offered, and the sink had to tell which mode it would like to have. Only after such an agreement was more than the USB-typical 5 volts switched on (if negotiated).
For security reasons, EPR goes one better in several respects: The negotiation of an EPR mode does not begin until both partners have agreed on an SPR connection beforehand. Unlike there, both partners must continue to talk to each other during the negotiation process: If the sink is muted, the source immediately switches off the high voltages and begins a new SPR negotiation at 5 volts. Conversely, a sink can ask to exit EPR mode at any time by requesting the SPR maximum of 20 volts again – and then again lower levels. A source then no longer needs to apply their EPR skills to avoid hopping between the two modes.
In addition to the fixed voltage levels, there have been modes for a long time in which the voltage can and should decrease dynamically over time. The latter is practical for smartphones, for example, because a lithium-ion battery is no longer charged linearly from a fill level of 80 percent or more. If the power supply takes care of a dynamic supply to match the charging curve, the charging electronics in the smartphone (which is limited in terms of space and waste heat) can be less complex.