DETAILS ARE EMERGING about a project by the IEEE to establish a standard smart DC power supply that could eventually eliminate the need to carry around power adapters.
The project began a year ago and hit the news recently when it received the backing of Taiwanese manufacturers. But it has received remarkably little attention considering that it promises to make life easier for all users, reduce the cost of electronic products and lead to a radical shake-up of the multi-billion dollar market for power adapters.
The IEEE, which governs basic standards such as Ethernet and WiFi, has set up a working group called P1823 to develop a specification for what it calls a "universal power adapter for mobile devices" - shortened inevitably, if inelegantly, to UPAMD.
This could turn out to be a misnomer because a UPAMD could also power household devices such as hi-fi equipment and televisions. UPAMDs could eventually be fitted as standard in homes, hotel rooms, trains, aircraft and cars so that a DC supply becomes as ubiquitous as the mains. Goodbye portable adapters.
The industry already has a standard 5 volt supply in the USB port, but even the latest power-boosted version, USB 3.0, can deliver only 4.5 Watts. One of the few parameters already decided for a UPAMD is that it should be capable of delivering between 10W and 130W per connection, enough for more power-hungry devices like laptops and printers.
A simplified version of the UPAMD vision is shown below, and almost every aspect of it is up for debate. Note that an adapter with just one output might look like a standard laptop power brick, but differs in that it can power any UPAMD-compliant device. Also, a UPAMD client can itself act as a UPAMD source, allowing you for instance to power one laptop from another when the battery runs flat.
The P1823 group has formed four subcommittees to deliver specifications respectively for power, communications, physical connections and conformity certification.
Even the basic physical link is fraught with complications. All cables will be detachable at both ends and to avoid confusion the connectors will not mate with any existing socket. Disconnection must be easy, to minimise damage or injuries caused by people tripping on cables.
One idea under consideration is a magnetic grip, but this could run into patent issues with Apple. Bob Davis, acting chair of the UPAMD project, says it could also fail because of a requirement for the connection to be strong enough not to break under high acceleration in a car or aircraft.
The connector also has to provide a communications link so that a client can report its requirements. Most laptop power adapters today use an analog feedback loop, with the source device sensing the battery level in the machine it is supplying. The UPAMD is likely to use digital communication.
A default supply at perhaps 12 volts will be available to allow communication with clients with flat batteries. For safety reasons the current will be limited to 50 milliamps until communication is established.
UPAMD power issues are complex but four options are being considered: a single yet-to-be-decided voltage with a tight tolerance, a single voltage with a broad tolerance, any voltage within a range, or a choice of several set voltages such as 12V, 24V and 48V, for example.
A single-voltage solution, whatever the tolerance, has the advantage of simplicity but might require the client device to do more work tailoring the supply to its needs. Davis says this is not as big an imposition as it sounds because DC-DC converters are between 90 per cent and 98 per cent efficient.
That still implies that conversions can waste between two per cent and 10 per cent of the input power as heat on mobile devices that have a very tight thermal budget. But Davis points out that a laptop has to do several DC-DC conversions in the laptop anyway.
He wrote in an email, "The majority of the power, other than charging the battery, goes to the processor at 1.0 volt at possibly 20 amps and down to 0.3V in sleep. On some of the larger processors it is at 1.1 - 0.9 volts at 50-plus amps.... Next generation 22nm devices will be using a lower voltage yet at higher currents."
Those currents exceed the projected 9 Amp rating on the UPAMD connector, so it cannot supply them directly; the power would have to be delivered at a higher voltage and lower current, and converted inside the laptop.
Davis admits that optimising the input voltage for each client device could be more efficient for some tasks. The power subcommittee has to decide whether the advantages of offering this flexibility justify the added complexity and cost.
Paul Panepinto, who chairs the P1823 power subcommittee, reckons a smart variable-voltage power supply would add only between $1.50 and $2 to the bill of materials, which would translate to about $8 more on the shop cost.
But there are considerable savings if you look at the power ecosystem as a whole. "The model [for power supplies in use today] is totally broken. The model says everyone has to take AC from the mains and turn it into DC power that is specific to every electronic device sold," Panapinto said.
"That means when you retire a device you throw away a power unit that may be in perfect working condition. And every time you buy a new device you buy a new power supply."
Panepinto personally favours a variable-voltage UPAMD, though he admits a vested interest in that he is vice-president of ecosystem development at Green Plug, which has been developing a smart variable-voltage supply for four years.
"If you are putting in communications there is no reason not to offer a power supply that will dynamically tune itself to the load," he said.
He gives the example of a laptop with a low battery. "If this has a fixed 19v input the internal charger has to drop the voltage to, say 5v, to match that of the battery. The conversion will involve a loss."
A smart variable-voltage supply could match the voltage of the battery dynamically as it charged up. This not only offloads waste heat from the client to the adapter, it is more efficient as it involves only one conversion.
Green Plug is launching a processor early next year that will do this. It is designed in partnership with Britain's Imagination Technology.
Panepinto insists that despite his personal preference all options remain open for UPAMD, and indeed Davis seems to favour a simple future-proof single-voltage device.
Davis said, "The goal is to be able to buy a UPAMD... and have it still viable for your grandkids to use and pass on." µ
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