Power Supplies Serve Up High Efficiency At Light Loads

Feb 1, 2007 12:00 PM
By David Morrison, Editor, Power Electronics Technology

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A series of 650-W to 1200-W ac-dc power supplies from Coldwatt leverages the company's control techniques and magnetics to achieve high efficiency across a range of load levels. The power supplies deliver 12-V output at efficiencies approaching 90% at full load, yet also achieve 80% or better efficiency at 20% to 40% rated power. This light-load performance is particularly significant as it represents the load range over which enterprise servers typically operate (Fig. 1).

High efficiency is achieved without sacrificing power density as the 650-W, 1000-W and 1200-W power supplies achieve 15 W/in³, 12.5 W/in³ and 15 W/in³, respectively. For IT managers and system designers, high efficiency in the power supply helps them address the challenges of increasing power and cooling requirements in the data center at a time when annual equipment operating costs due to power consumption may exceed the cost of the hardware being powered. Moreover, power conversion and power distribution account for roughly half of data center power consumption.

The three power-supply models are 1U modules that the company offers as part of 1+1 redundant power subsystems. These systems include rear-mounted power distribution boards (PDBs) containing dc-dc converters, which generate additional board-level voltages (Fig. 2).

To illustrate performance and features, consider the 650-W supply, which measures 40.25 mm high × 54.5 mm wide × 320 mm deep. The module generates two outputs: 12 V at 54 A and a 5-V standby supply at 3 A. Features include ORing FETs for achieving N+1 redundancy, hot-swap capability, active power-factor correction and a serial interface compatible with SMBus/I²C protocols. The unit specifies a universal input-voltage range and a 12-ms holdup time at 600 W.

The company offers a complete 1U power subsystem combining two 650-W modules with a PDB that generates four 12-V supplies at 16 A, one 5-V supply at 25 A, one 3.3-V supply at 12 A, and one -12-V supply at 0.5 A. The PDB measures 131 mm × 85 mm × 40.26 mm. According to Dan Artusi, CEO of Coldwatt, this subsystem is approximately half the size of what the industry has been using until now.

To achieve its high efficiency and high power density, the company has developed its own control algorithms and implemented them in silicon. According to the company, the control algorithms it developed for its power platform are tailored to application requirements. So, unlike off-the-shelf controller ICs that must accommodate a wide range of operating requirements, the Coldwatt controllers are optimized for best efficiency under the target conditions.

Coldwatt currently employs a hybrid analog/digital approach in which loop control is still analog. However, in future designs, the company plans to deploy a full digital approach.

Proprietary magnetics are also cited as an enabler of high efficiency. In this area, Coldwatt exploits magnetics circuits and topologies that were first developed at Rockwell Scientific, where finite element analysis tools were used to develop models that led to more efficient and repeatable designs.

In annual quantities of 600 to 1200 units, pricing is $143.51 for the 650-W unit, $211.06 for the 1000-W unit and $265.20 for the 1200-W supply. Coldwatt is currently shipping production quantities of the 650-W power supply and sampling the 1200-W system.

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