With the pressure to improve power supply efficiency, size, speed, and cost in modern electronic systems, power supply architecture has evolved from a bulky inefficient centralized power architecture (CPA) to compact high-efficiency distributed power architecture (DPA) and intermediate bus architecture (IBA). In the older CPA scheme, all the system voltages were generated at a central location and then distributed to the load via distribution buses (Figure 1).
This can be effective if the voltages are high and the currents are low, or if the distances between the power supply and the loads are small. However, today’s system requirements are different. Populated with new generations of microprocessors, memory modules, DSPs and ASICs, they require multiple low voltages with high current. In addition, the low-voltage loads are distributed across the system boards. As a result, with CPA, the distribution losses are higher and overall system efficiency is lower, which increases the thermal management cost as well as lowers the reliability of components.
Figure 1: In centralized power architectures, all the voltages are generated from a single housing and each voltage is bused separately to the load. (Source: Vicor)
To overcome the limitations of CPA, DPA was introduced in the early 1980s with the idea of decentralizing power to reduce distribution losses. In DPA architecture, the front-end AC/DC converter generates a fixed-DC bus voltage, such as 48 VDC. Most data centers and telecom equipment use 48 VDC bus voltage to power a number of isolated step-down DC/DC converters at the point of-load (POL). The POL converters then generate the required low voltages at high output current to drive the required loads (Figure 2).
Figure 2: In the traditional distributed power architecture, a DC-bus voltage, such as 48 VDC, drives a number of point-of-load (POL) isolated step-down DC/DC converters, which then generate the required low voltages at high-output current to drive the required loads.
The efficiency, along with the power density, of the isolated DC/DC converters used in the DPA scheme is high (typically, above 90 percent). But, with the use of nanometer processes, the voltages of these latest semiconductor devices, such as DSPs, memories and ASICs, have further dropped to 1 V and lower while the current requirements have risen simultaneously. In addition, these newest ICs are also demanding faster transient response from the DC/DC converters of the DPA. As a result, the step-down ratio for these POL DC/DC converters has gone upward, resulting in more losses, which in-turn is lowering the efficiency of these converters.
To deal with the multiplicity of lower voltages and higher current at POLs across system boards, more cost-effective and efficient converters with faster transient response were introduced as intermediate bus voltage. This scheme is called intermediate bus architecture (IBA). Introduced more than a decade ago, the IBA incorporates another DC/DC converter step in the traditional DPA architecture (Figure 3). As a result, the 48 VDC bus voltage is now stepped down to an intermediate voltage of 9.6 V or 12 V. This intermediate isolated DC/DC converter, called intermediate bus converter (IBC), is used to drive non-isolated POL (niPOL) buck regulators, reducing the POL function to regulation and transformation.
Figure 3: The intermediate bus architecture (IBA) incorporates another isolated DC/DC converter called intermediate bus converter (IBC) in the traditional DPA scheme, which further drives non-isolated POL (niPOL) buck regulators to generate regulated voltage for the load.
There are a number of power supply companies that offer high efficiency, high density IBC converters to facilitate IBA architecture. They include Bel Power Solutions, GE Critical Power and Vicor, to name a few. Bel Power, for example, offers fully regulated 420 W bus converter QME48T35120-NJBBGGE in quarter-brick format that is designed to deliver 12 VDC output at 35 A from a typical 48 VDC input. Peak efficiency at half load is around 96 percent. GE Critical Power is another major supplier in this race. Its fully regulated 400 W bus converter, labeled QBVW033A0B Barracuda is also a quarter-brick that is DOSA compatible. The input voltage range for this converter line is 36 – 75 V and the regulated output is 12 V. Typical efficiency at half load is 96.4 percent. For applications that require digital control, the company is offering QBDW033A0B Barracuda, which is a fully regulated, DOSA-compliant 400 W quarter-brick with PMBus interface. It is designed to deliver 9.6 to 12 VDC intermediate bus voltages for driving non-isolated POL converters. The input voltage range is 36 to 75 VDC.
For systems that need 300 W or lower output power, GE Critical Power has released an eighth-brick member, EBVW025A0B, that supports fully regulated 9.6 – 12.0 V output with DOSA compliance. Plus, it offers PMBus interface for digital control.