Electronic Design

Factorized Power Module Redefines The Wall-Wart

No longer just for on-board dc distribution to point-of-load, this maverick architecture promises higher efficiency from the mains to the load.

Previously, Vicor's Factorized Power Architecture (FPA) concept seemed constrained to a role as an alternative to the intermediate bus architecture (IBA). Now, the company's newest V·I Chip family member, the power factor module (PFM), takes the company from point-of-load to the ac wall plug (Fig. 1). With it, FPA promises significant reductions in ac-adapter size and increased ac-dc converter efficiency in converter configurations from wall-warts to silver boxes.

FPA is a response to the limitations of conventional distributed power. Current FPA products include the voltage transformation module (VTM), which is in some ways a point-of load (POL) alternative, and the pre-regulator module (PRM). Enhanced versions of both combine to make the PFM.

VTMs, which arrived in April 2003, are more sophisticated-than their conventional non-isolated POL brethren. They can function as either a step-up or step-down dc-dc transformer and can operate on a voltage significantly higher than the usual 12-V distributed on an IBA bus. A loop regulates the VTM's output by controlling input voltage.

Since the VTM isn't switching into an inductance, it can respond virtually instantaneously to a changing load. As a result, with a VTM, designers need less bulk capacitance to support fast load di/dt changes. Moreover, they can place the bulk capacitance needed for energy storage ahead of the VTM, thereby dividing it by the square of the VTM step-down ratio. Finally, a VTM, although more complex than an IBA POL, operates vastly more efficiently at high step-down ratios. This, in turn, permits the use of higher bus voltages.

Vicor followed up the VTM with the announcement of a PRM, a dc-dc converter module crafted to work with its VTMs. A PRM generates a controlled bus voltage typically several times higher than an intermediate bus voltage, resulting in lower voltage drops and reduced I2R losses on the bus.

The VTM's and PRM's isolation functions are reversed from the roles of the POL and upstream converter in the IBA. The VTM at the point of load provides isolation, not the PRM. Therefore, system designers can locate the regulation function anywhere in the system.

The new PFM contains what Vicor calls an adaptive VTM plus a microprocessor-controlled PRM. The adaptive VTM steps down the rectified line voltage, which is then sent to a special kind of PRM.

The VTM is "adaptive" in the sense that it automatically configures its own step-down ratio based on where it's being used. If the input is in the range of 90 to 132 V ac, as it would be in North America or Japan, the VTM parallels its input cells. If the input is between 180 and 264 V ac, as it would be in the rest of the world, it connects its input cells in series. Adaptability makes possible an improvement over conventional ac-dc converters, which take an efficiency hit of around 3% when wrangling with the ac mains in Japan or North America.

The PRM in the PFM is like Vicor's earlier PRMs, but with power-factor correction. This is provided by an on-board microcontroller that monitors the PRM and adaptive VTM outputs to generate a control signal to an in-module ASIC. The ASIC both regulates the output and provides shaping of the module input current to achieve power-factor correction.

The PFM's microcontroller also can communicate with the rest of the system via its PMBus. In addition, the microcontroller monitors the module's input power, providing the capability to switch to an alternate source for continued operation or to a hold-up capacitor for graceful degradation.

The most interesting application area for PFMs may be laptop ac adapters. Vicor is working with customers on two different kinds of prototypes (Fig. 2). One would involve replacing a conventional adapter's boost converter, downconverter, and separate dc input boost converters (that handle 12-V mobile power) with a single PFM. Doing so would increase power density by a factor of about five while reducing wasted power by around 4.5 W.

A more aggressive approach would be what Vicor calls a factorized power adapter (Fig. 3). It would maintain the Adaptive VTM (along with a rectifier/filter) in the unit that plugs into the wall, while locating a PFC PRM, energy storage, and a battery charger inside the laptop. This substantially reduces the size of the external adapter. It also boosts power density by a factor of 10 and cuts external power dissipation to only 3.8 W.

Evaluation samples of the V·I Chip PFM will be available in November. Production quantities are slated for the first quarter of 2006. As of this writing, target price is under $40. A preliminary data sheet is available now.

Vicor Corporation

TAGS: Vicor
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