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Power Electronics

Bus Converters Push Power Levels Higher

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It's only been a few years since dc-dc converter manufacturers began introducing bus converters for use in intermediate voltage bus architectures (IBAs). But in that short time, the power density of these isolated dc-dc converters has increased significantly, just as the number of performance options available has risen.

In the typical IBA, the bus converter steps down a 48-V input to an intermediate voltage bus somewhere in the 5-V to 12-V range. Nonisolated point-of-load converters (POLs) may then be used to generate the other lower-voltage supplies required on the pc board. The bus converter provides isolation but does not necessarily need to provide regulation. For example, in computing applications where the bus converter takes its power from a regulated 48-V source, an unregulated bus converter can simply provide a fixed-ratio voltage transformation.

Such bus converters are referred to as dc transformers. Like the fully regulated dc-dc converter “bricks,” these bus converters are designed for a nominal 48-V input. But unlike the fully regulated bricks, dc transformers are designed for operation over a narrower input-voltage range than the 36 V to 72 V demanded in telecom equipment.

By reducing the regulation requirements and narrowing the input voltage range, the dc transformers can achieve higher efficiencies and greater power output than the standard bricks. Some of the recently introduced models promise as much as 97% full-load efficiency. Consequently, some bus converters now specify output-current ratings as high as 50 A in a quarter-brick package.

Despite the high efficiency, significant amounts of heat must still be dissipated at such high power-output levels. In order to maintain high current ratings at high ambient temperatures, through-hole rather than surface-mount interconnect is the norm among higher-current bus converters. In addition, some units have provisions for heatsinking, and most units rely on airflow to minimize derating. For example, Power-One's QTS48T46096 maintains its 46-A, 9.6 V output at ambients up to 80°C with 400 LFM of airflow or 70°C with 200 LFM.

As new bus converters continue to be introduced, output current ratings are expected to go even higher. For example, by the fourth quarter, Bel Power, a division of Bel Fuse, plans to introduce a 5-to-1 fixed-ratio quarter-brick bus converter rated for 56 A at 9.6 V.

In addition to the dc-transformer type of bus converters, there are models that offer either semi-regulated or fully regulated output. A semi-regulated output may be useful in powering high-performance POLs with narrow input voltage ranges, which are more common and easier to apply than the wide-input range POLs. Some bus converters specify the full 36-V to 72-V input range to enable their use in telecom applications. And some with the full-input voltage range also may provide a fully regulated output, just like conventional bricks.

Some of the recently introduced bus converter models are listed in the table, along with a few of their key specifications. Note that beyond these basic parameters there are many performance features, such as operation over temperature, programmability and fault protection, that distinguish one model from another and suggest their suitability for a given application.

Table. Recently introduced bus converters for IBAs.
Artesyn Technologies IBC38AQT, fixed ratio 42 to 53 37.5 A at 12 V (450 W) 95.5% typical Quarter-brick June 2005 Available now
Artesyn Technologies IBC30AQS, semi-regulated output 42 to 53 30 A (360 W) 94.5% typical Quarter-brick June 2005 Available now
C&D Technologies QBC-12/22-L48, fixed ratio 40.5 to 57 22 A at 12 V (264 W) 96% typical Quarter-brick February 2005 Available now
C&D Technologies EUS models 4-to-1, 5-to-1 or 6-to-1 fixed ratio 36 to 55 25 A at 9.6 V (240 W) 94% typical Eighth-brick September 2004 Available now
Cherokee International CBQ5, 5-to-1 fixed ratio 38 to 55 33 A at 9.6 V or 350 W 96.5% typical Quarter-brick July 2005 Now sampling
Bel Power 07CM-38S10L, 5-to-1 fixed ratio 36 to 55 38 A at 9.6 V 96.5% typical Quarter-brick November 2005 Available now
Bel Power 07CR-25S10L, 5-to-1 fixed ratio 36 to 55 25 A at 9.6 V 96% typical Eighth-brick November 2005 Available now
Power-One QTS48T46096, 5-to-1 fixed ratio 36 to 55 46 A at 9.6 V or 500 W 97% typical Quarter-brick March 2005 Available now
SynQor BusQor HEA, fully regulated 35 to 75 30 A at 12 V (360 W) 95% typical Half-brick July 2004 Available now
SynQor BQ55090ETA27, 5-to-1 fixed ratio 35 to 55 27 A at 9.6 V > 95% typical Eighth-brick June 2005 Available now
Tyco Electronics Power Systems QBK033 series, semi-regulated 36 to 60 up to 33 A at 12 V (400 W) 94% typical Quarter-brick April 2005 Samples available
Vicor VIC-in-a-Brick, Intermediate (fixed ratio with 3-V to 48-V output) 38 to 55 50 A at 12 V (up to 100 A or 600 W at other voltages) 96% typical Quarter-brick January 2004 Available now

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