APEC 2014 is over. Held this year in Fort Worth, Texas, the annual IEEE power electronics conference left me with a number of impressions. The first is that the PMBus standard has finally been vindicated. Another is that gallium-nitride (GaN) power transistors are evolving in interesting ways. Finally, there are some interesting developments in Power over Ethernet (PoE) and at a clever university startup.
PMBus All Over The Place
The Power Management Bus (PMBus) arrived on the scene about the same time I started as the Analog/Power Editor for Electronic Design. I came on-board in May, 2004, so I missed that year’s APEC. The following March, “Digital power” was the big buzzword at the conference, and one aspect of it was PMBus. (The other large issue was managing the feedback loop for regulation in dc-dc converters in the digital domain. That also has become non-controversial for most power folks.)
PMBus was and is a variant of the two-wire System Management Bus (SMBus), intended for the digital management of power supplies. What makes it different from SMBus is its suite of commands for functions like turning the supply on and off and setting a fixed output voltage, as well as its ability to read back operational and environmental parameters on demand.
After a promising start, PMBus went into eclipse in 2008, when a jury in a patent lawsuit found that any communications bus used for controlling power supplies violated the intellectual property (IP) of power supply company Power-One, now part of ABB. It took several years after that to work out a royalty system satisfactory to all parties. (See “Power-One’s Z-Bus And Patents”)
Those days are now behind PMBus. At APEC this year, many companies introduced new regulator devices that were designed to be compatible with the latest PMBus release, PMBus+ V1.3. The new spec supports a separate adaptive voltage scaling (AVS) bus for controlling processor voltages. AVS deals with process and temperature variation between multiple devices in real time by continuously updating the voltage requested from the power supply. Manufacturers of FPGAs, ASICs, systems-on-chip (SoCs), and processors in the networking, communications, and computing markets all have requested it as a feature.
GaN Reliability Data
I also chatted with Carl Blake, senior advisor of marketing at Transphorm. The company has been boasting of its position in practical GaN devices for several years at APEC. This year, Carl was pleased to announce that Transphorm had complete data about reliability of its products’ failure rates under voltage stress to show the world. He was particularly tickled because one of the speakers in the plenary sessions had pointed to the lack of such data as an indicator that GaN technology was not yet mature. Blake did acknowledge that there was still no reliability data relative to thermal stress, but promised that it would be available before the next APEC conference. (Watch the Video.)
Better Things To Do With GaN?
Also on the topic of GaN, I had a short chat with Alex Lidow of Efficient Power Conversion (EPC) about new and novel applications. When he founded the company, the vision was always on power semiconductors. But different applications have cropped up since EPC began shipping products, and the range of applications has stretched far beyond the power realm. Applications that are real today include lidar for autonomous vehicles and envelope tracking for output power control in cellular devices.
Going beyond transportation, evolving medical applications for lidar include a colonoscopy pill that patients swallow and excrete. The pill is much smaller than anything like that I have reported on before, but the idea is the same. It broadcasts what it sees as it travels through the intestines. What’s new is that it is so inexpensive (potentially) that it needn’t be recovered after use.
(Watch a video of my chat with Alex that describes some of the other applications.)
90 W On PoE
Akros Semiconductor demonstrated its work in PoE, which has grown from a way of powering non-video Voice over Internet Protocol (VoIP) phones up to a maximum of 15 W to LED lighting an office cube with up to 90 W. The secret is to “use more pairs.” The tricky part is managing the feedback from the powered device to the power source equipment (PSE) so an Ethernet switch with PSE doesn’t cost more than it has to.
Spinning Capacitors For Isolation
The most intriguing booth was way in the back of the hall for a startup created by some folks from the University of Wisconsin-Madison. The company, C-motive, has developed a way of feeding power to a rotating machine through a capacitor in which one of the plates (about the diameter of a 5-in. disc drive; in fact, it helps to think in terms of the physics of disc drives) spins with the motor shaft. The tricky part is that both plates are flexible and the face of one of the plates is micromachined so aerodynamic forces shrink the air gap to a very short distance. C-motive even had a working demo.