Advanced power supply topologies improve efficiency without cost penalties
BY LAURENT JENCK
ON Semiconductor
Phoenix, AZ
http://www.onsemi.com
With an estimated 2.5 billion electrical products in use in the U.S. alone, and with 400 to 500 million new power supplies sold every year, improving power supply efficiency is absolutely essential to meeting energy efficiency standards, reducing the pressure on global energy resources, and mitigating the impact of our use of technology on the environment. However, power supply implementation or selection often comes late in the overall product development process, leaving little time to optimize the design for the target application and leaving little flexibility in terms of cost of acquisition. Driven by advancing technology and both voluntary and mandatory standards, the energy efficiency of power supplies is increasing.
The need
As a result of economic growth, rapidly evolving technology, and expanding populations, world energy consumption is projected to grow by a staggering 50% between 2005 and 2030. This equates to a leap from 462 quadrillion BTU in 2005 to 695 quadrillion BTU in 2030 (Source: Energy Information Administration).
Such high levels of energy consumption are not naturally sustainable and will have an increasing impact on the environment and the lives of the global population because the traditional answer to rising energy demand has been to increase supply by building more power plants fueled by coal, natural gas, nuclear energy, and petroleum. While research development and implementation of renewable energy in the form of hydropower, biofuels, wind, and solar power has grown significantly, our dependence on fossil fuels means that we must become markedly more efficient. This is both in terms of how we use electrical products as well as their inherent energy efficiency.
Initiatives
In the U.S., it is estimated that energy-efficiency initiatives could reduce energy use by 10.6 quadrillion BTUs about 10% of projected U.S. energy use in 2020, according to analysis by the American Council for an Energy-Efficient Economy (ACEEE).
Initiatives such as Energy Star have been very successful and are now used to identify compliant products in a total of approximately 60 different categories. There are ongoing efforts to harmonize energy efficient guidelines by gaining acceptance of Energy Star around the world. To date, Europe, China, and Australia have signed agreements to recognize the initiative.
Some governments have adopted a stronger stance by implementing mandatory standards. Given the environmental challenge ahead, this looks to become an increasing trend.
Some countries tighten standards regularly to foster constant improvement. Japan’s Top Runner scheme, for example, identifies the most-efficient appliances on the market in different categories, and then requires all competing brands to improve on them within four to six years. Those that fail face financial penalties. All the regulations around the world, whether mandatory or voluntary, target wasted power of power supplies in standby mode and active mode.
Supply types and options
Power supplies for electronic devices can be broadly divided into linear and switching (or switch-mode) power supplies (SMPSs):
Linear power supplies have a very simple design. SMPSs meanwhile are more complex. Linear power supplies have a typical efficiency ranging from 40% to around 55% while SMPSs can achieve much higher efficiency ratings, ranging from 60% to 95%.
In terms of straight efficiency comparisons, it is easy to see that SMPSs offer the best option for designers seeking to meet either voluntary or mandatory standards for their new products. However, two other factors may affect the adoption of power supplies.
Cost. The greater complexity of SMPSs typically means a larger bill of materials compared to linear power supplies. Also, more-advanced, more-efficient, tighter-tolerance components used in some topologies tend to be more expensive than basic performance derivatives. Linear power supplies have a simpler design, but use components such as iron core transformers that require large amounts of copper for their windings — this can have an impact on cost. Overall, incremental costs for SMPSs are modest and sometimes lower than those for inefficient linear power supplies.
In order to nurture widespread adoption of the more-energy-efficient SMPS approach, it is important for costs to be comparable or lower than those of linear power supplies. This is because ultimately when consumers are presented with two products with identical performance they will tend to opt for the one with the lower ticket price. Whilst consumers are becoming more environmentally aware and beginning to consider total cost of ownership — that is, the initial purchase cost plus the energy costs to use the product through its lifetime – this is a notion that has been slow in gaining traction.
Size. Linear power supplies are typically larger and heavier than SMPSs. For external power supplies this is less of an issue than for designs that integrate the power supply functionality into the product housing. In this scenario linear power supplies not only use up valuable space, but as a result of their low efficiency also generate large amounts of waste heat that must be thermally managed in order to ensure the long life and reliability of the equipment. Heavier power supplies may also present an issue if the piece of equipment into which they are used is designed to be portable.
SMPS advanced topologies
SMPSs with higher efficiency, smaller size, and less weight represent the way forwards. With the support of advanced integrated ac/dc controller and regulator devices such as those offered by companies like ON Semiconductor, new topologies that support the drive for cost-effective high-efficiency SMPS designs can be implemented.
Many of the losses associated with SMPSs can be associated with switching. Soft-switching topologies such as half-bridge and full-bridge can overcome these losses. In addition to improving efficiency, these topologies also help drive up power converter density (measured in W/in.3 ) — a key requirement for many new product designs. Topologies that had previously been used only in high power applications (for example, 500 W or 1 kW), are now finding their way into medium- and lower-power applications (for example, 100 W) because of the impact they can have on efficiency and power density.
Reference designs
Reference designs such as ON Semiconductor’s GreenPoint (see Fig. 1 ) provide manufacturers with turn-key solutions that meet or exceed the minimum energy efficiency standards in a wide number of applications such as desktop computers, set top boxes, notebook ac/dc adapters, and LCD TVs. By providing tools that make the design of efficient products more straightforward, the route to a scenario where the majority of electronic products achieve efficiency levels in the region of 80% or 90% will be accelerated. It is estimated that employing reference design approaches such as GreenPoint could increase the efficiency of home products by as much as 20% and office equipment products by 15%.
Fig. 1. Reference designs such as ON Semiconductor’s GreenPoint, which provide manufacturers with a turn-key solution to help them meet or exceed minimum energy efficiency standards.
High-efficiency SMPSs can dramatically increase the efficiency of electronic appliances. Now that there is general parity in SMPS and linear power supply costs, great opportunities exist to significantly increase the efficiency of many types of products. This will help equipment producers meet and exceed the demands of both voluntary and increasingly prevalent mandatory energy efficiency standards. The growth in the use of electronics products set against the sustainability of energy sources means that things have to change; significantly improving power supply efficiency can play a major role in achieving those goals. ■
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