Power-supply design trends are clear and dramatic: additional features, improved efficiency, and smaller size for the same power ratings, for both battery-powered portable units as well as larger, line-powered ones. For the AC-DC supplies, these changes are due to multiple factors combining to yield these more-compact designs. Some of the factors are obvious, but others are not.
Start with the most apparent change, which is the use of smaller passive components. Vendors are shifting the basic resistor and capacitor footprint from 0805 size (2.0mm by 1.25mm) to 0603 (1.5mm by 0.8mm), and to an even-smaller 0402 size (1.0mm by 0.5mm). Diodes, as well, are also available in smaller packages. The use of larger parts was a holdover habit from previous generations of supplies. It made sense for vendors to continue using parts, which were fully known and characterized in their supply chain and inventory, and all of the same size.
The pressure to reduce supply size, along with the electronic industry's growing use of smaller parts in consumer products, has made them the body size of choice. The result is a significant reduction in required PC board space -- the change from 0805 to 0402 cuts a component's immediate footprint to 20 percent of its previous value -- and there are many such devices on a supply's PC board.
Changes in the supply magnetics (inductors and transformers) are also helping reduce size. Traditionally, these components have been the most complex “simple” passive ones in the supply's implementation, often custom-designed by the OEM to get precisely the desired and often subtle combination of primary- and secondary-tier parameter values (including inductance, DC resistance, size, form factor, winding type, insulation, orientation, volume, and cost).
In addition, supply designers are making better use of the available inductor volume. For example, they are reorienting the inductor to take advantage of the supply's available height-dimension headroom, in return for a smaller footprint.
On the active component side, the power semiconductors’ packaging has shrunk, primarily for the critical MOSFETs of the output. Chip-scale power MOSFETs such as the DirectFET from International Rectifier (where the metal enclosure covering the bare die is also the drain terminal) provide significantly more power capability, but in a smaller package. This has had a major impact on supply size, since the DirectFET has a 30 percent larger MOSFET die but with a 60 percent reduction in PC board footprint compared to the widely used D2Pak package. Compared to the D-Pak package, the DirectFET die can be 33 percent larger than the D-Pak package, yet its footprint is 54 percent smaller.
Power-supply size also involves the necessary concerns for thermal loads. To address this issue, engineers are making extensive use of thermal gap pads for more efficient heat transfer. Since this thermal material can be a significant part of the bill of materials (BOM) cost, the heat-sink structure has been redesigned to use less of the gap-pad material, thus cutting both cost and size.
mrdon, it's bad enough that commoditization means cheaper--often too cheap--materials and/or construction. But when the very thing that's one of a product's key characteristics--in this case a power supply's efficiency--is sacrificed by purchasing/accounting, that just beggars belief. I mean, trading off specs and features is part of the process but sounds like you had an exceptionally bad experience.
William, that's exactly what's been needed--for power supplies to become commodities so they'd be cheap enough and small enough. At least that was the push 20 years ago. But at that time, I didn't hear anyone complaining about what would happen when components were cheapened to reach that goal. Now I think we're all aware a lot more, as both designers and consumers, of the effects of this problem, whether it's cheapo plastic gears in clocks or sub-efficient power supplies.
Ann, You and TJ are absolutely correct about small size vs cost. One of my biggest challenges in developing LED Lighting fixtures while working at Hunter Fan was power supply efficiency, small size, and cost.To achieve a quality power supply, efficiency cost is part of the Product Development financial equation. I was able to obtain superb power supply efficient (99%) and small size using good PFC based components and proper PCB thermal management techniques, but the cost was something the Bean Counters couldn't stomach. Unfortunately, efficiency was the design parameter they could leave without.
Lower power/smaller size is only expected. What is troubling about the trend for the DIY/learning crowd, how does the average human place a 0603? Not easily. Will through hole components stay, or will pre-mounted small form factor take over? I am sure the price or old-style components will increase. The size and style of the through-hole resistor hasn't changed in decades, and they stay relevant.
Not only are the power supplies getting smaller, but many of them have become commodity items, with the result thatr there is a lot of price pressure. Unfortunately that tends to lead to a reduction in quality from many suppliers, while others chgarge a bit more for a better product. Consider that some of the better suppliers are able to sell a supply for amost twice the price of what others offer, a product with similar size and power ratings. So evidently in some areas quality and robustness still matter.
TJ makes a good point about price, of course. On a different price note, back when, some power supply designers said they could make advances closer to what was needed in size and efficiency, but that it would cost an arm and a leg to do so.
mrdon, those are exactly the reasons I was hearing 20 years ago that power supplies needed to get smaller, let alone more efficient. IR has long been in the forefront of advances in power supply design and manufacturing. At one time (maybe more than one?) industry pundits have said that power supplies were a major roadblock in advancing the state of electronics.
Ann, As pointed out in the article, todays electronics are getting smaller in size but the power requirements are going up. It's great that power semiconductor manufacturers like International Rectifier are developing technologies that meet both design requirements. I agree, its nice to see the arrival of this semiconductor technology in power electronics.
Thanks for reporting on this. I remember hearing about 20 years ago that power supply designers were trying to make their products smaller, but it was a tough job to make that happen. Looks like progress has been made since then.
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