标签: converter

We are aware that switching power supplies (converters), whether AC/DC or DC/DC, are almost always more efficient than linear versions. We also know that the weight and size difference is also dramatic, as well as much more tangible and immediately apparent. But sometimes, you have to see the two power supplies side-by-side to have that reality hit you.   Recently, while rummaging through my collection of AC/DC converters (aka "wall warts"), I came across two from way back in the day for an Iomega ZIP drive from around 1995.   The supplied Iomega ZIP drive linear converter (left) and the replacement switching converter (right) both produce a 5 V/1 A DC output, but with very different weight and size.   The numbers for these units, both rated at 5 V/1 A, are dramatic and tell the story beyond just efficiency, which I didn't measure:   - Original unit: 510 grams (18 oz), 55 mm x 80 mm x 55 mm - Replacement: 70 grams (2.5 oz), 45 mm x 50 mm x 25 mm   That’s a huge savings in weight and size: the switching unit is about 1/7 the weight and ¼ the size of the linear one shipped with the drive.   Physically large and hefty linear supplies and converters used to be the standard, of course. I have and still use an Analog Devices model 956 AC/DC converter, rated at 5 V/2 A.   Don't drop this 5 V/2 A linear supply, you could break a toe—but it does inspire confidence due to the size and heft, which were considered state-of-the-art at the time, circa 1977. This epoxy-potted unit comes with four #4-40 threaded inserts for mounting it to a PC board or chassis with screws -- very convenient and necessary.   Not only is it is still working, but due to its heft and size (865 grams, 110 mm × 68 nn × 50 mm), it exudes an aura of providing "serious" power compared to a small, lightweight switcher, even if that aura may be a self-imposed, projected image I have created. You don't mess with this supply, is what it seems to say to the world.   I recently saw one offered on eBay for $60 (why would you want one?) and it says the original price was $525—another example of super-shrinkage, compared to a new switching 5 V/2 A unit.   Do you have any other examples of dramatic change in weight and size, besides the often-cited ones of processors, ICs, phones, and storage?

Recent teardowns I've written have highlighted the circuitry differences between hardware powered by batteries, therefore containing DC voltage regulation circuitry, and mains-powered equivalents containing more elaborate AC-DC converters. These discussions reminded me of a newly unveiled product, the Batteriser (here's the patent ), which was recently shown in AA-sized prototype form to a select set of journalists (yours truly not included, in the interest of full disclosure). The Batteriser is forecast to begin production-shipping in AA, AAA, C, and D cell-compatible form factors in late September, crowdfunded by an Indiegogo campaign . Founding company Batteroo's pitch is rich with intrigue and compelling claims: - Industrial espionage, - Up to 8x longer battery life - Products that "pay for themselves with the first set of revived batteries" And at minimum, the Batteriser, "crafted from stainless steel at 0.1 mm thin," represents an impressive Moore's Law case study of the now-possible extreme miniaturization of today's DC voltage boost and regulation capabilities. But what, if any, reality is there behind founder Bob Roohparvar's boasts? Plenty of detractors exist; see, for example, the commentary at Hackaday and Slashdot . Here are my thoughts. In his pitch to PC World's Jon Phillips , Roohparvar reportedly showed via a "power meter" that adding the Batteriser to an AA battery that had been drained to 1.3V restored the battery's like-new 1.5V output capabilities. I've no doubt that this is possible, but the "power meter" likely put a scant current demand on the setup. The Batteriser-boosted battery might not have fared nearly as well under more typical applications ("wireless keyboards, game console controllers, TV remotes, digital scales, blood pressure monitors, toys, and (of course) the ubiquitous flashlight"), especially when drained all the way down to 0.6V as Roohparvar suggests is feasible. Secondly, why couldn't the requisite boost and regulation circuitry alternatively be located within the powered device itself? In fact, as you likely already realize, it frequently is. Roohparvar happened to find a Bluetooth keyboard that wouldn't function reliably with 1.3V non-Batteriser'd AA power sources. But debunker Dave Jones , in spite of lots of searching, was unable to find an AA-based product that wouldn't work with batteries running at above 1.1V . And since battery discharge cycles are non-linear, that 1.1V level represents around 80% of a battery's full life. What about Batteroo's cost-savings claims? Each AA-sized Batteriser is forecast to cost $2.50; that's $10 for a four-pack, plus the prices of the batteries themselves. But I recently came across a 100-pack of alkaline AAs for $15 . Even if you buy into Roohparvar's pitch that a single Batteriser-enhanced AA can replace eight conventional counterparts, the comparative math just doesn't add up ... especially if, as Dave Jones claims, use of the Batteriser might lead to a short circuit-induced system fire . And what about Batteroo's advocacy about keeping an excessive drained-battery count out of landfills, which would normally resonate strongly with an avowed environmentalist such as me? Thankfully, batteries are no longer mercury-filled , although tossing them in the trash is still illegal in California. But why not instead invest in a set of NiMH rechargeables, which can be cycled thousands of times? Here, for example, is a g eneric twelve-pack of AAAs for $7.99 . And here's a brand-name twelve-pack of AAs for $14.99 . The charger's extra, of course, but the adder is scant; here's one for $12 that even comes with four AAs . At the end of the day, although I commend Batteroo on its miniaturization achievement, I struggle to find a strong commercialization market opportunity for it. And attempting to rationalize early-adopter's investments in your company by means of dubious-at-best claims is penny-wise, pound-foolish. But having said this, there may be some angle on the product that I've overlooked, which might lead me to a more positive opinion. If you see it, I'd like to hear about it. Please post your thoughts in the comments.     Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance. He is also a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company's online newsletter. And he's an off-hours freelancer as the Principal at Sierra Media, where he contributes to (among other things) the Brian's Brain blog at EDN Magazine. Brian has a BSEE from Purdue University in West Lafayette, IN.

One of my pet peeves is when a datasheet lists 'typical' values with no min or max. It seems like this problem is getting worse as components get more complex. In fact, one FAE admitted that “typical” specs are often driven by marketing’s needs, not engineering analysis. Sometimes the results are almost laughable. TI, which generally does a good job of characterizing their devices, has a step-down converter (the TPS82740A) whose Iq is rated at 360 nA typ, 2300 max. That’s a huge range of values. One can only conclude that the typ number is meaningless. (Not to knock the part – this is a very innovative converter. It will stop switching and connect Vin to Vout through a FET if Vin is roughly at the desired output level. Very cool.) Maximum values are especially rare in the domain of ultra-low power MCUs. Vendors are in a real slugfest to prove their parts have lower sleep currents than the competitors, and too often “typ” is the only rating given for this critical parameter. Here’s a “typical” example from a vendor of an ARM MCU who makes a big production about their low-current specs:   The careful designer is left scratching his head, with no idea what sort of results he’ll see in a real-world application. Hats off to Freescale. Perusing the datasheet for their KL02 Cortex M0+ MCU I came across the following statement: “The maximum values stated in the following table represent characterized results equivalent to the mean plus three times the standard deviation (mean + 3 sigma).” Wow! A year or so ago I asked several semi-vendors what ‘typical’ means and none could define it. Here’s a concise mathematical model that makes a lot of sense. Three sigma means you can be sure 99.7% of the parts will not exceed the listed values. 'Typical' still is not defined, but cautious engineers really only care about max values. A portion of the table that the three sigma rating applies to follows:     It’s interesting that typ and max are generally pretty close together. If typ is the mean – which is only a guess – then the standard deviation they experience is pretty tiny. They have extremely good control of their manufacturing process. Other members of their Kinetis family are well characterized as well. Some, like the KL03, sip very gently from the power supply in deep sleep modes. It’s tempting to advertise the best possible numbers for important specs, and ‘typical’ results are a lot more compelling than worst-case values. But these are aspirations, not guarantees, and we engineers can’t design to some marketing person’s fantasy. I hope more companies follow suit.

Having product choice is good, there's not much question about that. When you can select from among a wide variety of products in a given category—whether at the supermarket, consumer-electronics vendor, or book source—you're likely to find something that you want, at a price you feel is OK, and the competition among products works to the consumer's benefit. But at the same time, it can become overwhelming. I recently was looking for a basic digital camera ($100 range) to replace a Canon Sureshot (8 Mpixels) which was operating erratically after several years of hard life. I decided to start with Canon again, since I assumed that their newer models would likely have a similar user interface, form factor, and functions as the one I had. I checked out the Canon site and was soon overwhelmed with the number of basic cameras and families they had. For some of them, their niche was obvious, such as ruggedized or water-resistant. But for others, I could not see the actual differences, except by a careful read-through of the product specifications. I soon felt like the fellow in the Max Ernst painting to the left, Man's head puzzled by the flight of a non-Euclidean fly . I don't mean to pick on Canon here. I found out that it's the same when you look for a GPS unit: so many families and so many products within each family, and that's just from a single vendor. Some are clearly targeted (such as for hikers or bikers) but still, an overwhelming set of choice remained. What I really needed from the vendors was a decision tree or selection flowchart, and most don't have that. I suppose somehow it makes sense to have so many models each with their own twist; I certainly don't understand the nuances of production and distribution in the consumer-product business. But you do have to wonder if the cost of having all the different production runs and sub-runs, bills of materials, labeling, packaging, documentation, order-entry set-up, and support wipes out whatever market and profit benefit there is to having so many similar products. We engineers would never do anything so foolish, right? Or maybe we would . Look at the product portfolio of any major analog IC vendor, for example, and you'll see an astonishingly wide and complex array of offerings for basic building blocks, such as op amps or converters. Yes, each one has its place and role, but still, it's a lot to look at and decide among. Some components, for example, are truly outstanding in one or two parameters, and are "merely" pretty good in others. In contrast, other offerings may not be especially outstanding in any one specification, but are very, very good in many of them. These are complex and subtle tradeoffs that the designer has to make when working the BOM when judging which one to use. Fortunately, most vendors offer selection guides to help you narrow down your choices, based on your needs and priorities. Do you find product proliferation in consumer end-products to be a problem? Has it ever caused you to just "give up" because you couldn't decide which model to get?