Offline bus converter module maximizes system efficiency, minimizes heat losses
February 27, 2010 | Paul Buckley | 222900635
Joe Sullivan, Product Marketing Manager, Vicor Corporation explains how an offline bus converter module can minimize heat losses while maximizing system efficiencyOver the past quarter century or so, businesses - banking, insurance firms, dispensers of online music, search engines, and everyone else - have become ever more reliant on the computer. Data centers or server farms have been proliferating worldwide to satisfy the demand, but, of greater interest here, they are becoming more massive. Because they need increasingly more power, which, of course, is more costly, efficient operation has become a high-priority. Since 100 percent efficiency is not achievable, the management of the heat generated is also a high priority.
So small size, high efficiency, and heat management are valuable attributes for any element in the system, but the elements that comprise the system depend to some extent on the architecture of the system.
Electricity is generated somewhere and it is distributed to the user (to the data center, say) where it is further distributed, usually in a number of steps. Somewhere along the line, it is changed from AC to DC for final consumption by arrays of processors at increasingly smaller voltages and higher currents. Efficiency drops at every conversion (AC to DC, a higher voltage to a lower voltage), so it is desirable to keep the number of conversions low. Much more power is wasted when it is distributed at lower voltages (and higher currents) because of I2R losses, so it is desirable to distribute at high voltage.
High voltage from the power line is converted to a lower voltage by some means, whether it is done in a silver box, which is typical of computer type applications, or whether it is done in a central office application. These applications typically start with AC power from the utility. In order to get DC the AC voltage needs to be rectified, and it is typically line reference to ground; therefore, it needs to be isolated and down converted.
The VI BRICK BCM (bus converter module) Array is a high efficiency (typically 95 percent), high-power vertically-mounted BCM array (see Figure 1) that provides isolation and conversion from 380 V to 12 or 48 V for low-voltage distribution near the point of load. The device incorporates the technical attributes of VI Chip technology in a robust package that facilitates thermal management.
The new VI BRICK BCM Arrays are ideally suited for server applications using a PFC front end that require relatively high power levels with challenging thermal issues. The offline power can be bussed to the motherboard and converted to either 48 V or 12 V, which minimizes distribution losses, reduces conversion steps, improves efficiency, and reduces overall cost. These products can be used in a wide variety of applications that require high efficiency, high power density, improved thermal management, low noise, fast transient response, and overall design flexibility.
Ideal for PFC front-end applications providing the capability of a high voltage bus with minimal distribution losses, the VI BRICK BCM Array provides a highly efficient solution for applications using point-of-load (POL) converters to provide output voltages. They are available with 384 and 352 nominal input voltages and output voltages of 11, 12, 44, and 48 Vdc. The efficiency and compact size of these modules yields power density up to 290 W/in³ and fast transient response.
Less capacitance is required for energy storage near the load, which equates to space and cost savings. Due to its fast response time and low noise, the need for limited life aluminum electrolytic or tantalum capacitors is reduced – or eliminated – resulting in savings of board area, materials and total system cost. In addition, the BCM power train has a capacitance multiplication feature: the input capacitance normally located at the input of a regulator can be located at the input of the BCM. Since the K factor of a BCM array is 1/8, that capacitance value can be reduced by a factor of 64x.
These models provide output power up to 650 Watts in a board space of less than two square inches in a 1U high package that measures 89,9 x 14,2 x 28,7 mm.
The high power and compact size of the BCM array modules yield power densities up to 290 W/in3, resulting in a very small footprint on the PC board.
An important attribute is that VI BRICK BCM arrays are easily paralleled. Each array has up to 650-Watt output capability. If more power is needed, multiple arrays can very easily be put together to create a larger array for higher power such as for a server or in telecommunications. When connected in an array with other BCMs (all with the same K factor), the BCM module will inherently share the load current with parallel units, according to the equivalent impedance divider that the system implements from the power source to the point of load. It is important to know that, when started, BCMs are capable of bidirectional operation (reverse power transfer is enabled if the BCM input falls within its operating range and the BCM is otherwise enabled). In parallel arrays, because of the resistive behavior, circulating currents are never experienced because of the energy conservation law.
A couple of examples demonstrate the distribution of a high offline voltage (including the AC to HVDC 'silver box' for rectification, EMI and inrush current protection, and power factor correction) to the motherboard for final distribution on the board. Incidentally, the silver box is simpler at this high voltage stage reducing its size by more than 50 percent.
The example in Figure 2 shows the post-'silver box' 380 Vdc distributed directly to the blade, which virtually eliminates distribution losses because the I2R loss is 0.1 percent of the loss that would have been incurred if the distribution had been done at 12 V. Obviously, at 380 V, the wiring and connector sizes and costs are much less. The 380 V to 12 V conversion is done on the blade, leaving minimal distance to the voltage regulators.
The example in Figure 3 also shows the post-'silver-box' 380 Vdc distributed directly to the blade with the same high-voltage distribution benefits. In this case, however, the conversion on the blade is 380 Vdc to 48 Vdc. The voltage regulators have been replaced by PRM-VTM pairs, which convert the 48 V to1.x V at the highest efficiency and the smallest conversion package at the load. This arrangement minimizes on-blade distribution loss.
Both the VI BRICK PRM and VTM can achieve higher than 96 percent efficiency. Overall efficiency for a power system – including the combination of a PRM and a VTM – operating from an unregulated DC source and supplying a low-voltage DC output typically ranges from 90 to 95 percent. In many cases, it is possible to achieve overall efficiency exceeding 92 percent even at full load. With higher efficiency comes lower total heat dissipation, another important consideration in power systems design.
Please login to post your comment - click here
- No news
MOST POPULAR NEWS
- Touch screen technology goes behind the display
- Japan prepares to become world's largest solar revenue market in 2013
- Smart grid sensor market looks set to double in size by 2014
- Single-chip solar energy harvester operates wireless mesh nodes
- Bosch drives down fuel consumption - in a salami technique
- World's lowest power Bluetooth smart chip is unveiled
- Ceramic material drastically shrinks power supplies
- Lithium-ion batteries withstand 10.000 charging cycles
- Solar industry capital spending hits seven-year low in 2013 but upturn is on the cards
- 300 percent increase in battery life with low power Bluetooth wireless speaker module
- 60V Buck-Boost Controller Drives High Power LEDs
- Energy Measurement and Security for the Smart Grid
- Dangers of Aftermarket Counterfeit Battery Packs
- High Voltage Surge Stoppers Ensure Reliable Operation During Power Surges
- Motor-Drive Design made Simple
- Adaptive Cell Converter Topology Enables Constant Efficiency in PFC Applications
- Micropower Isolated Flyback Converter with Input Voltage Range from 6V to 100V
- Derating of Schottky Diodes
- Heatsink Optimization
- High Performance ZVS Buck Regulator Removes Barriers To Increased Power Throughput