Bus Converter Enables High-Voltage Distribution

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

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Vicor's high-voltage V•I Chip bus converter module (BCM) steps down a 384-Vdc input to an isolated but unregulated 12-Vdc output, while achieving a power density of greater than 1000 W/in³. The B384F120T30 module is rated for 300 W (25 A at 12 V) of output, but multiple BCMs may be paralleled to increase the current, or series connected to raise the output voltage. Because of these capabilities, the B384F120T30 presents a building block for implementing advanced systems of high-voltage power distribution in the data center or for improving power density in conventional power systems.

The industry is exploring the use of a high-voltage dc bus as a means of reducing power-distribution losses in data centers. With its ability to step down a 384-Vdc supply rail in a small form factor (1.28 in. × 0.87 in. × 0.26 in.), and with its high efficiency (> 95%), the B384F120T30 eases the implementation of high-voltage power distribution.

As an example, Vicor cites a server blade application in which four BCMs are paralleled to generate a 48-V supply rail on the blade. That supply rail is then stepped down to chip-level voltages using the company's preregulator modules (PRMs) and voltage-transformation modules (VTMs), which are also V•I Chips (Fig. 1).

Meanwhile, in more conventional server and telecom power systems, the bus converter can be used to increase the power density in the dc-dc converters that follow the power-factor correction stage. For applications where the 12-V output is desired, output current can be scaled by paralleling the modules without requiring additional circuitry, thanks to the positive temperature coefficient of the bus converter's output impedance. The company has paralleled up to 10 modules to produce 3 kW of output. Fig. 2 charts efficiency versus load when four BCMs are paralled to produce 1200 W at 12 V.

Another benefit of the B384F120T30 is its ability to minimize the capacitance requirements. Consider an application where a 12-V power rail feeds multiple point-of-load converters (POLs) that generate lower supply voltages. In a typical application, capacitance would be required on the input of each POL. However, because the BCM acts as a low-impedance current multiplier, the POL input capacitance at 12 V can be transferred to the input of the BCM at 380 V. And since energy stored in a capacitor is proportional to voltage squared, the capacitance requirement decreases by (12/380)², or approximately a factor of 1000.

The BCM uses the sine amplitude converter technology found in Vicor's VTMs, but adds soft-start and protection features needed in the high-voltage bus converter applications. Despite the additional circuitry, the B384F120T30 has the same dimensions as other V•I Chips and is similarly compatible with standard pick-and-place machinery and assembly processes.

The B384F120T30 is priced at $37.50 each in OEM quantities and is available from stock. Single 300-W BCM evaluation boards and two 1.2-kW demo boards (12-V, 100-A outputs or 48-V, 25-A outputs) are also available. For more information, see www.vicorpower.com.

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