Vicor – Migration of power distribution from 12V to 48V: an accelerating trend

Today’s design engineers are constantly pushing the boundaries of power components’ performance by designing systems that feature:
• More processing capability
• Higher communication rates
• Added peripherals
• More torque in electric motors
• Brighter LEDs

To provide more functionality and performance, the system tends also to consume more power. But the ability to meet this increased power requirement is often constrained by size and/or weight restrictions.

In a bid to overcome this constraint, a growing number of product types are moving from 12V as the voltage for power distribution to a 48V distribution bus. This article describes the benefits of 48V for power distribution, and the key challenges that designers face in implementing a 48V bus.

Why migrate to 48V?
Power losses in the distribution system are equal to I2R: lowering the current by raising the voltage therefore has the effect of reducing losses. Power losses are of course detrimental to system efficiency, but they can also reduce the power supplied to the load, given the limitations of the system’s cables, connectors and PCB.

And typical loads are rising in many applications. As an example, the power consumed by the processor in servers has increased from less than 100W some years ago to 300W or more today. Distributing this increased power to multiple processors gives rise to more losses, unless mitigated by distribution at a higher voltage, or by the use of larger copper bus bars – which is not always possible or desirable. Any design with an increased power requirement will suffer from higher losses proportional to the square of the current.

Fig. 1: 48V power schemes support the heavy power demands of stationary vehicles

Fig. 1: 48V power schemes support the heavy power demands of stationary vehicles

Higher-voltage distribution reduces transmission losses: for example, a 48V power distribution scheme loses 16 times less power than a 12V scheme supplying the same load. This is a striking reduction: it might seem surprising, then, that any designs still use 12V for power distribution, but of course the truth is that there is a very wide range of components configured to operate on 12V systems.

The use of a 48V distribution bus, however, enables substantial efficiency, cost, size and weight improvements, and this is leading to increased interest in 48V design.

The start of 48V power: telephone systems
We can thank the development of the modern telephone and telephone exchanges for the earliest use of 48V, which has now become the standard for the communications industry. This is because of the efficiency advantage: it produces a lower voltage drop over distance as a percentage of the operating voltage, as well as enabling the use of smaller gauge wire, simpler battery back-up – which also explains the use of a 48V with a negative reference – while operating at a voltage level considered to be safe.

The new 48V
Many consider the use of 48V in domains other than communications equipment to be the ‘new 48V’ since, unlike a telephone system, it is positive-referenced, has no lightning or surge requirements, and has a more limited range of 30V-60V.

Fig. 2: Warehouse lift truck – the latest Cat® designs operate at 48V

Fig. 2: Warehouse lift truck – the latest Cat® designs operate at 48V

Voltages below a 60V DC limit are classed as Safety Extra Low Voltage (SELV). A 48V power scheme thus reduces distribution losses while maintaining the ease of handling of a SELV arrangement.

Today, 48V distribution is used in data centres, automobiles, LED lighting, industrial equipment and even power tools. In fact, so common is 48V now that it is impossible to go through a typical day and not use several 48V-powered systems.

Data centres lead the way
Data centres and supercomputers are particularly heavy users of electrical power; efficiency is a critical operating requirement for them. With interest in artificial intelligence surging, it seems likely that the demand for more computing power will only grow, and therefore that processors will continue to stretch the capabilities of existing power systems.

Supplying these higher levels of power to processors while maintaining efficiency presents physical challenges when using a traditional 12V system. Therefore engineers have turned to 48V distribution to enable the higher levels of power distribution and overcome these challenges.

Google adopts 48V
One example of 48V usage is by Google. At the Applied Power Electronics Conference 2017 and Open Compute Project 2017 events Google’s engineers openly discussed the merits and cost savings to be gained from implementing 48V power distribution in the company’s data centres.

Another example of 48V adoption was highlighted at Supercomputing 2017, when the recent Green500 ranking was announced. The Green500 ranks the most-efficient high-performance computer systems. This year, four of the top five ranked systems were designed by PEZY, a Japanese company which has deployed 48V distribution throughout its computer systems.

Commercial LED panels grow brighter and cost less
IT and communications are not the only sectors with growing power demands: commercial lighting systems are also getting ever bigger and brighter. New York’s Times Square illuminations are a case in point: the enormous, outdoor LED screens used in installations such as this are far bigger than they were even ten years ago.

LED panels continue to benefit from improved performance, delivering higher LED pixel density and brightness. The engineers designing these new panels are moving to 48V distribution, reducing the size and weight of the power cables while also increasing the efficiency. In addition to enhanced efficiency, these larger systems also benefit from reduced weight, making installation easier. Today a matrix of smaller panels are assembled together to create a single brighter, longer-lasting display which is easier to move and install.

48V power distribution also provides a cheaper and safer alternative to the AC distribution schemes used in retail store wall displays and the information displays found in train stations and airports.

Fig. 3: Vicor’s Cool-Power ZVS regulators step down a nominal 48V input directly to the voltage required at the point of load

Fig. 3: Vicor’s Cool-Power ZVS regulators step down a nominal 48V input directly to the voltage required at the point of load

Power tools: more torque, longer run-times
Consumer and professional battery-powered tools are following a similar trend, moving to higher voltages for more power. More power enables longer run-times between charges and higher torque.

The operating voltage of the batteries in cordless tools has steadily risen, from 9V to 12V to 18V to 20V to 24V, and now to 48V and even 60V.

Battery-driven power tools from brands such as DeWalt and Greenworks now operate at 60V. Likewise, lightweight yard tools such as Snapper’s high-performance chainsaws and mowers operate at 60V.

Automotive is driven to adopt 48V
Mild hybrid petrol/electric cars increase fuel efficiency by 10% or more compared to pure combustion engine-based vehicles. Automotive engineers at suppliers such as Delphi are using 48V power distribution schemes for mild hybrids to take some load off the internal combustion engine. They do this by powering accessories during the Stop phase of Start/Stop operation, as shown in Figure 1. Initial designs deployed a 12V battery scheme, but this could not power all of the cabin features during the Stop phase. A 48V scheme has proven to be the most efficient alternative.

Powering robotics and industrial equipment
Industrial equipment is starting to use 48V for the same reason: a higher power requirement.
• Kiva Systems, which makes robotic fulfilment equipment for large warehouses, is using 48V to support Amazon’s warehouses.
• Advantest uses 48V to minimise wire size in its automated test equipment.
• Caterpillar offers 48V Cat® warehouse lift trucks, as shown in Figure 2.

Process control, manufacturing equipment and factory automation equipment are additional product types which are using a 48V distribution bus.

48V is the new 12V
The message to be drawn from the above is: if more power is needed, consider 48V. Engineers are finding the losses caused when increasing the power throughput in 12V distribution schemes are impairing the performance and value of their designs.

The enhanced 48V converters and regulators available today provide comparable levels of efficiency and performance to 12V counterparts, at a comparable cost, size and weight. Many power designs are benefitting from the additional advantage of replacing intermediate-stage regulators with a single regulator that converts directly from 48V to the load voltage, instead of first regulating to 12V.

The number of suppliers providing 48V DC-DC converters has increased over the past few years. Vicor provides 48V DC-DC regulators and isolated converters which achieve very high levels of efficiency, density and performance, as shown in Figure 3. There are several reasons for the superiority of Vicor’s 48V converter range:
• The use of high-efficiency switching topologies such as zero-voltage switching
• 3D packaging technology which enables high-density power components. The SM-ChiP package is a good example of this.

In addition, engineers designing 48V systems have access to Vicor’s online selection and design tools, which reduce design time and help the designer to implement an optimised solution.