Vicor Power Modules Simplify High-Voltage Conversion for the Shift to 48 V

Power delivery networks for high-performance computing, automotive, robotics, and industrial systems are shifting from 12 V to 48 V architectures, and the reason is rooted in basic physics. Power lost in a distribution path P is I squared times R, so the loss rises with the square of the current. Raising the distribution voltage from 12 V to 48 V cuts the current needed to deliver the same power to a quarter, which drops the conduction loss significantly and lets you use lighter, thinner conductors. The challenge, however, is that decades of systems have been optimized around 12 V distributions, and the loads usually run at low voltages, so you must bridge your high-voltage source to a 48 V bus, and onward to the point of load, without giving back the efficiency you set out to gain. Vicor tackles this issue with its high-performance power modules and a power architecture built specifically around 48 V.

Fixed-ratio conversion with Vicor’s bus converter module

The primary component of Vicor’s high-voltage to 48 V story is the Bus Converter Module (BCM). A BCM is a fixed-ratio converter whose output is a fixed fraction of its input, defined by a conversion factor Vicor calls the “K factor,” rather than a value the converter actively regulates. This distinction is what allows a fixed-ratio stage to achieve exceptional efficiency and density. The BCM is built on Vicor’s Sine Amplitude Converter topology, which operates in three stages: primary-side switching converting DC input into a sinusoid; an ideal-transformer stage scaling the voltage by its turns ratio, and secondary-side switching converting the sinusoid back to DC.

Since it behaves much like a transformer with a fixed turns ratio, a BCM is often described as a DC transformer. Consequently, Vicor’s high-voltage BCMs can step 800 V or 400 V down to a 48 V safety-extra-low-voltage (SELV) output at peak efficiencies up to 98%, and with a very high power density. The BCMs can be paralleled into arrays to increase power and series-connected at their outputs to reach even higher voltages, giving system architects a flexible building block rather than a fixed-function product.

Eliminating intermediate stages

What makes the fixed-ratio bus converter useful is how it simplifies the rest of the system. Vicor BCMs transform a high-voltage battery into a virtual low-voltage battery, presenting a lower impedance path and a fast transient response, allowing the HV source to directly and responsively feed a 48 V network. In an electric vehicle, this fast response lets the BCM replace the 48 V battery, reducing weight and saving space. The same property also serves robots and unmanned vehicles where a BCM can isolate and step down a high-voltage battery or tethered high-voltage feed to a 48 V SELV bus.

Why the Sine Amplitude Converter runs so efficiently

The efficiency and density figures a BCM achieves are not incidental, but derived from how the Sine Amplitude Converter operates. While the topology resonates, its switching devices commutate when the voltage across them is near zero, largely suppressing the switching losses that typically rise with frequency. This soft-switching behavior is what permits the converter to run at a very high resonant frequency, reducing the size of the magnetics and filtering. Operating the power transformer at a single resonant point, rather than across the wide range a regulating converter must sweep, also means that the transformer can be wound for one optimized condition.

The fixed-ratio nature of the scaling stage also compounds the advantages. In the case of a regulating converter, it has to hold its output steady against a moving input, which involves carrying control-loop margin, reserving duty-cycle headroom, and tolerating the losses that come with constant correction. A fixed-ratio converter avoids all of that, because it is not trying to regulate at all; it transforms its input by a set ratio and lets the rest of the system handle regulation where it is actually needed. The result is a stage with a very low output impedance and a fast response, capable of feeding a 48 V network without the sag a standard converter would show under a sudden demand.

Regulating the 48 V bus with DCM

A fixed-ratio bus converter establishes the 48 V bus, but many loads need a regulated voltage, which is where Vicor’s DCM converters come in. The DCM is a regulated DC-DC converter; the isolated DCM takes a wide, unregulated input and produces an isolated regulated output, while Vicor’s non-isolated DCM modules bridge a 48 V bus to a regulated low-voltage rail. The recent DCM3717 and DCM3735 (Figure 1), for example, operate from a 40 V to 60 V input, produce an adjustable regulated output around 10 to 12.5 V (12.2 V nominal), and can be paralleled to scale system power.

Figure 1: High-density DCM modules for bridging 48 V and legacy 12 V power buses. (Image source: Vicor)

Conclusion

Vicor’s ecosystem covers conversions across 800 V, 400 V, 48 V, and 12 V, allowing designers to assemble a path from a high-voltage source down to the point of load with compatible modules, and preserve 12 V investments by bridging 48 V and 12 V rails.

To explore the modules and architectures behind high-voltage to 48 V conversion, visit Vicor’s Converting High Voltage to 48V Efficiently product highlight.