Equipment vendors may be changing batteries from one design to the next. But in many cases, they may stick with the same power adapter, which not only supplies power for battery charging but also may power the device for extended periods of time when an external source is available. Available in wall-plug or desktop enclosures, these supplies generate single-voltage outputs ranging from a couple of watts up to about 70 W. These units offer a number of advantages over embedded power supplies.
Taking the power adapter circuit out of the equipment being designed allows for a smaller equipment design. It also transfers some of the burden in obtaining safety and EMI approvals from the equipment vendor to the power-supply vendor, and it simplifies requalification of a product when changes are made outside the supply.
As was the case with battery-charger circuits, linear versus switcher is the main distinction among power adapters. Linear-style adapters have a reputation for being low-cost but bulky ("bricks"). These supplies are still popular in many applications that require just a few watts. But switch-mode power adapters, with their smaller size, lighter weight, and greater efficiency, are gaining ground overall despite the fact they may cost more at the lower power levels. Additionally, emerging standards for power-supply efficiency provide further motivation for adopting switch-mode adapters.
In many consumer and business applications, customers will accept the additional cost of a switcher (perhaps a 20% premium over a linear) in exchange for its small size and light weight. It also offers advantages such as a universal voltage input and more flexible packaging options. Switchers can be made sleeker and less obtrusive, whereas linears are normally limited to a boxy shape because of their transformers.
This last point is important as more portable applications demand an adapter that blends into the design. Responding to this need, power-supply manufacturers such as EOS Corp., Camarillo, Calif., are getting more creative with their packaging (see the figure). Still, the main goal in adapter design is to make it smaller.
With this goal in mind, power-adapter vendors are developing some very-high-density switch-mode adapters with ratings of 10 W/in.3 and higher. According to Jim Schultz, executive vice-president of sales and marketing at EOS, such gains make it possible to replace a brick-sized linear supply that normally weighs 5 to 8 lb with a switch-mode version that weighs just 5 oz. Despite its small size, such a supply could produce 45 W of output.
These high power densities are made possible by the use of highly efficient circuit architectures that reduce requirements for heatsinking, through use of ASICs that reduce component counts, and by the use of high-quality capacitors and other passive components. For example, EOS reports that it achieves greater than 92% efficiency using a resonant-conversion switching technique.
Steven Willing, marketing director for imaging and mobile electronics at power-supply manufacturer Astec, indicates that design-automation tools are another element making higher- density adapter designs a reality. These tools let power-supply designers simulate electrical, thermal, and EMI performance so they can fine-tune their designs.
Nevertheless, there's a price premium when it comes to purchasing power adapters with the most power per unit volume. Willing cites as an example two 70-W switch-mode desktop adapters that he recently quoted. A version of this supply with just under 10 W/in.3 was priced at 25% to 30% above that of a low-density brick-shaped version with 2 W/in.3 Besides the tradeoff between size and cost, size can be traded for other parameters. A larger adapter design allows for better management of heat, which results in greater reliability.
New standards for green electronics also will impact adapter selection. To reduce the energy wasted by external power supplies that remain plugged in, the European Commission is drafting specifications for allowable standby power. In creating products for the European market, Willing advises designers to consider the current draft of specifications as guidelines (Table 4). Although these guidelines are still at the committee level, a formal agreement is expected shortly. Barring improvements in the linears' efficiencies, these specifications should lead to a phasing out of linear-style power adapters in Europe.
Such standards can be expected to provide added incentive for development of smaller, more efficient adapters. These advances, when combined with improvements in Li-ion batteries and associated charging circuitry, will help make portable equipment more portable while expanding the performance capabilities of these products.
Equipment vendors may be changing batteries from one design to the next. But in many cases, they may stick with the same power adapter, which not only supplies power for battery charging but also may power the device for extended periods of time when an external source is available. Available in wall-plug or desktop enclosures, these supplies generate single-voltage outputs ranging from a couple of watts up to about 70 W. These units offer a number of advantages over embedded power supplies.
Taking the power adapter circuit out of the equipment being designed allows for a smaller equipment design. It also transfers some of the burden in obtaining safety and EMI approvals from the equipment vendor to the power-supply vendor, and it simplifies requalification of a product when changes are made outside the supply.
As was the case with battery-charger circuits, linear versus switcher is the main distinction among power adapters. Linear-style adapters have a reputation for being low-cost but bulky ("bricks"). These supplies are still popular in many applications that require just a few watts. But switch-mode power adapters, with their smaller size, lighter weight, and greater efficiency, are gaining ground overall despite the fact they may cost more at the lower power levels. Additionally, emerging standards for power-supply efficiency provide further motivation for adopting switch-mode adapters.
In many consumer and business applications, customers will accept the additional cost of a switcher (perhaps a 20% premium over a linear) in exchange for its small size and light weight. It also offers advantages such as a universal voltage input and more flexible packaging options. Switchers can be made sleeker and less obtrusive, whereas linears are normally limited to a boxy shape because of their transformers.
This last point is important as more portable applications demand an adapter that blends into the design. Responding to this need, power-supply manufacturers such as EOS Corp., Camarillo, Calif., are getting more creative with their packaging (see the figure). Still, the main goal in adapter design is to make it smaller.
With this goal in mind, power-adapter vendors are developing some very-high-density switch-mode adapters with ratings of 10 W/in.3 and higher. According to Jim Schultz, executive vice-president of sales and marketing at EOS, such gains make it possible to replace a brick-sized linear supply that normally weighs 5 to 8 lb with a switch-mode version that weighs just 5 oz. Despite its small size, such a supply could produce 45 W of output.
These high power densities are made possible by the use of highly efficient circuit architectures that reduce requirements for heatsinking, through use of ASICs that reduce component counts, and by the use of high-quality capacitors and other passive components. For example, EOS reports that it achieves greater than 92% efficiency using a resonant-conversion switching technique.
Steven Willing, marketing director for imaging and mobile electronics at power-supply manufacturer Astec, indicates that design-automation tools are another element making higher- density adapter designs a reality. These tools let power-supply designers simulate electrical, thermal, and EMI performance so they can fine-tune their designs.
Nevertheless, there's a price premium when it comes to purchasing power adapters with the most power per unit volume. Willing cites as an example two 70-W switch-mode desktop adapters that he recently quoted. A version of this supply with just under 10 W/in.3 was priced at 25% to 30% above that of a low-density brick-shaped version with 2 W/in.3 Besides the tradeoff between size and cost, size can be traded for other parameters. A larger adapter design allows for better management of heat, which results in greater reliability.
New standards for green electronics also will impact adapter selection. To reduce the energy wasted by external power supplies that remain plugged in, the European Commission is drafting specifications for allowable standby power. In creating products for the European market, Willing advises designers to consider the current draft of specifications as guidelines (Table 4). Although these guidelines are still at the committee level, a formal agreement is expected shortly. Barring improvements in the linears' efficiencies, these specifications should lead to a phasing out of linear-style power adapters in Europe.
Such standards can be expected to provide added incentive for development of smaller, more efficient adapters. These advances, when combined with improvements in Li-ion batteries and associated charging circuitry, will help make portable equipment more portable while expanding the performance capabilities of these products.