Electronica: Ericsson sees benefits in digital power

Ericsson believes that dynamic voltage control that is possible on a intermediate power bus allows designers to make energy use more efficient in heavy load applications such as data centres. Steve Bush takes a look at the arguments

Ericsson Power Modules is proposing the design of an agile 4-12V regulated intermediate bus to save power in energy-hungry data centres.

With intermediate power busses, traditional 48V distribution-level power is converted to an intermediate voltage bus, 12V for example, for distribution across a PCB. This relatively high voltage keeps current down, and therefore I[super2]R losses.

Each high-consuming load or load cluster gets its own ‘point-of-load converter’ to supply chip Vcc – generally 3V or lower.

At the Electronics Goes Green (EGG) congress in Berlin, Ericsson argued that this solution is wasteful in the gaps between data processing surges when power demand is low.

“The choice of 12V has been made to ensure a high enough voltage to deliver all the power required by the board, or load, in times of high data traffic. However, this approach becomes highly inefficient when the traffic demand is low,” said the firm.

Its solution is to have a variable intermediate bus voltage that can be modulated along with the processing load.

“Dynamic bus voltage is an evolution of the intermediate bus architecture and provides the possibility to dynamically adjust the power envelope to meet load conditions. It achieves this by adjusting the intermediate bus voltage via the use of digital power control and optimised hardware combined with energy-optimising algorithms,” said Ericsson.

“This is a technology that makes possible to reduce board power consumption from anywhere between 3 and 10%, depending on the board application,” added Patrick Le Fèvre, marketing director at Ericsson Power Modules.

In data centres, power needed for cooling has a multiplying effect on power dissipated on PCBs, with 1W of board load requiring 0.5-1W of cooling.

According to Ericsson, is can be worse: “1W saved at the board level can result in a 3W saving at the power grid level.”

The firm has implemented its agile bus concept in two 48V to intermediate voltage DC-DC converters.

BMR456-DBV is a greater than 400W 13.0-8.2V output quarter brick, with extension to 4V for sleep.

BMR457-DBV is a 300W (25A) 13.2-8.2V output eighth brick, with extension 6.9V for sleep.

Both products implement digitally-controlled voltage tuning algorithms on ARM7TDMI-S processors.

Output voltage to be adjusted via PMBus (rev 1.2) commands or preset profiles stored by the system designer in built-in memory.

These are the first converters to be implemented on the firm’s FRIDA II platform. This platform was introduced by Ericsson at the beginning of the year for use in telecoms power supplies, particularly those in Advanced Telecommunications Computing Architecture (ATCA or AdvancedTCA) applications, or for remote telecom equipment supplied from unstable power sources.

Digital control allows switching parameters to be controlled on-the-fly for maximum efficiency without component count getting out of hand.

“Exploiting the possibilities offered by its core processor’s fast response and computational abilities, the embedded firmware integrates a fast response-loop algorithm,” said Ericsson. “The algorithm adjusts parameters to guarantee output voltage will always be contained within a narrow band-gap, and remain tightly controlled whatever the input conditions, over the input voltage range from 36 to 75V.”

Input voltage transients with slew-rates up to 0.5V/µs can be handled while keeping the output voltage within +/-10% to avoid triggering over-voltage protection.

“It also manages pre-bias start-up operation, and shut down is controlled avoiding voltage spikes that cause avalanche conditions in the secondary-side synchronous rectification mosfet, making a contribution to further improve reliability,” claimed the firm.

The power architecture is isolated (2,250V input to output), with full-bridge drive to the transformer primary and a centre-tapped dual half-bridge arrangement on the secondary.

The power converters are available in 36-75V (+/-2% output tolerance) and 40-60V input ranges.

Power density in the smaller one is 129-147W/in2, 126-140W/in2 for the quarter brick, and there is an optional base plate for high temperature applications.

Typical peak efficiency (12V out, half load) is 95.2 or 96.4% respectively.

Feed forward regulation is included for input transients, and droop load sharing for 10% tolerance is available over 36-75V inputs

Converter’s physical size is 58x23x10mm or 58x37x11mm.

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