Green power takes centre stage
Energy conservation has become a major focus for electronic products no matter where they are to be sold around the world. Legislation and customer pressure are both working to ensure greener operation.
In the European Union, for example, under the EcoDesign Directive, manufacturers of energy-related products need to be able to demonstrate they have taken environmental factors into account. The European Commission has introduced a number of ‘implementing measures’ that specify the kinds of actions that manufacturers of electrical and electronic equipment need to put in place to improve their environmental performance.
The first implementing measure to be put in place focused on standby power consumption. The first move was to cut power consumption when devices are switched off to 1 W or less and to 2 W for systems running in standby mode. From the start of next year, these limits are halved to 0.5 W and 1 W, respectively. Other legislation focuses on power-factor correction (PFC) to ensure that electronic devices and lighting systems do not adversely affect the electricity supply.
Power Integrations has developed a range of components to target the increasingly stringent requirements for standby power and PFC. The company’s SENZero and LinkZero devices provide the building blocks needed to cut standby and off-mode power dramatically. For better PFC performance, Power Integrations has developed the Qspeed advanced diodes. These diodes combine an extremely low reverse recovery charge (QRR) with a very soft recovery waveform. By replacing existing ultra-fast diodes with the Qspeed devices, manufacturers can improve the efficiency of PFC circuits and switching power supplies by a significant factor and run cooler by more than 50 per cent.
At a higher level of integration, the Power Integrations’ Hyper series of components for mid and high-power industrial PSUs offer simpler circuits and higher efficiencies complete with support for PFC. The commission has followed up with implementing measures that focus on the energy usage of products that range from televisions and set-top boxes to lighting and electric motors.
As they see the cost of energy rise, customers are demanding greater attention to the power consumption of their systems. Data-centre operators are focusing heavily on the operational cost of their systems and are prepared to pay to reap the benefits of lower electricity bills. This in turn is changing the way PSUs are designed – putting the focus not on the traditional peak efficiency but on how well the PSU performs across its output range.
A data-centre PSU is typically loaded at 20 per cent of its rated power capacity. But the peak efficiency of many traditional PSU designs is only obtained when the PSU is running at 80 per cent of its power capacity or more. The efficiency of traditional architectures can drop off rapidly as the load decreases. This is because switching losses begin to dominate the equation.
Although legislation is not yet targeting the data center, computer manufacturers have opted to move in the direction of greater efficiency for differentiation and also to offer customers operational cost savings. The highest-profile campaign is the 80 PLUS initiative. The idea behind 80 PLUS was first presented at the American Council for an Energy-Efficient Economy (ACEEE) Market Transformation Symposium and was quickly adopted as the basis for PSU efficiency marking by the Energy Star programme. By the end of 2007, several hundred PSUs on the market were certified to the original 80 PLUS standard, which demanded PSUs could provide efficiency of at least 80 per cent down to 20 per cent of the rated peak load.
In 2008, the standard was revised to accommodate the demand for higher efficiency and greater cost savings. The Bronze, Silver and Gold classifications pushed efficiency at 20 per cent load up to 82, 85 and 87 per cent, respectively. In 2009, the Platinum category was added, which increased the 20 per cent load efficiency to 90 per cent.
The lifetime energy and cost savings for data centres simply by using these higher-efficiency PSUs are immense. By using 80 PLUS Gold-rated PSUs, a high-end can save between 30 MWh and 50 MWh during its lifetime. Because they offer higher efficiency, the servers also suffer less thermal stress and exhibit higher reliability from running cooler, which helps overall lifetime.
Using knowledge obtained from seven design centres around the world for standard and custom power supplies in the communications sector, Murata has become a world leader in the business for Gold and Platinum 1U front-end PSUs. The company provides products that offer 400W in the smallest 54mm-width housing up to 2800 W in a single power shelf. The S1U-3X shelf design supports for power ratings up to 6000 W.
Energy-efficient design does not just apply to the front-end modules that have embraced the 80 PLUS initiative. Energy-efficient design ripples through the entire system. Most computer and telecom servers, for example, employ distributed power architecture in which one or more front-end PSUs supply electricity to a tree of intermediate and point-of-load (POL) DC/DC converters. The distribution voltage is higher than that required by most digital integrated circuits (ICs) as this minimises cabling and PCB track losses.
A commonly used distribution voltage is 12 V and conversion from this level down to the 1 V or 2 V needed at the POL is seeing high levels of innovation from PSU manufacturers not just in power efficiency but density. An example is the EN5339QI made by Enpirion. Essentially a power system-on-a-chip (PowerSoC), the EN5339QI uses high-speed MOSFET technology to support very ultra-high switching frequencies. This design results in a 20 per cent footprint reduction and 40 per cent lower profile compared to previous Enpirion 3A design. The PowerSoC integrates the controller, power MOSFETs, compensation network and inductor in a 4 mm x 6 mm package and provides an efficiency rating up to 95 per cent.
Another supplier focusing on efficiency is Aimtec a relatively new entrant in both the AC/DC and DC/DC segments. The company offers AC/DC PSUs in chassis mount and units that can be soldered onto the PCB up to 150W.
Digital control is becoming increasingly common in distributed-power architectures. Leading manufacturers have chosen to support the PMBus as a way of managing and monitoring the performance of POL converters and their loads. The PMBus is an open protocol developed specifically for power-systems management. It is a serial bus, based on the System Management Bus (SMBus), itself a variant of the widely used I2C serial bus. The SMBus is already in use in computer servers so the addition of PMBus is a straightforward choice.
Commands and responses are sent over the PMBus between a system management unit and power controllers on plug-in boards or to the POL converters themselves. Products such as the GE Energy DLynx series offers customers the ability to use the communications protocol to optimise power conversion. As well as providing for monitoring and adjustment, the commands make possible complex designs to improve efficiency and detect faults automatically.
The PMBus makes it possible to manage power consumption dynamically by controlling the performance states of components such as microprocessors. For the example, the Advanced Configuration and Power Interface (ACPI) makes it possible for external logic to prevent a processor from going into a high-speed, high-energy state or send it to sleep. Thanks to techniques such as system virtualization, these functions are now being used in data-centre servers to ensure that software workloads are processed using the minimum energy states of the various processors in the system.
The management protocols keep thermal stress – and the need for air conditioning – to a minimum by preventing hotspots from forming. Workloads on overused processors that might cause the device to operate at a high clock speed, which will force up its energy usage, can be spread evenly among other processors that are more lightly used. Processors that are not needed at any given time can be sent to sleep and the power to those modules reduced accordingly, all under the management of the PMBus. Standardisation around PMBus makes it possible for suppliers to focus on improving capabilities and cost, not on reinventing the wheel.
Ericsson Power Modules offers both Advanced Bus Converter (ABC) and POL devices with PMBus communications. Recently, the company introduced 250 W to 300 W BMR457 Eight Brick series modules as well as the Quarter Brick BMR456 series offering 12 V at 400 W to 468 W. The digitally controlled DiPOL modules for POL use offer PMBus-compliant read and write functions and come in 12 A, 20 A and 40 A versions.
Delta is introducing digitally controlled brick power modules with PMBus support, starting with 600W-capacity models and will move onto higher power levels after the end of 2012. The company is also moving into the Intermediate Bus Converter arena for high-voltage datacom systems, providing 11 V at 50 A from a 350 V nominal supply in a half brick.
For front-end power, Emerson Network Power’s DS1200 range of distributed modules offer not just PMBus compatibility but models that offer compliance with the 80 PLUS Platinum efficiency rating.
The result is a range of offerings that deal with the demand for energy efficiency coming from both governments and customers.