Power House

Analog Applications Spotlight: Anthony Fagnani

Gayle Bullock — Thu, 23 May 2013 18:45:00 GMT

I'm pleased to welcome Anthony Fagnani to the Power House blog. Anthony is the mind behind the article "Synchronous rectification boosts efficiency by reducing power loss" featured in TI's Analog Applications Journal newsletter.

Welcome Anthony!

What is the problem/challenge you saw that spurred you to write “Synchronous rectification boosts efficiency by reducing power loss”? As an applications engineer at Texas Instruments, my group had just released our first wide VIN synchronous boost controller, the TPS43060 and TPS43061. I really wanted to take a closer look at the benefits of synchronous rectification in a step-up application. While testing, I thought others might be curious also. That’s when I decided I would write it up to share and hopefully help others.

Measured efficiency and power loss in a low-duty-cycle application

What was the most difficult aspect of the topic you wrote about and why? The topic was pretty straight forward to write up and test. The hardest part may have been finding the time to do so!

Who and what application do you think this article is best suited for? This article is applicable to anyone looking to design a step-up converter at a high current where synchronous rectification can provide a benefit. This covers a very wide range of applications from industrial to those powered by a battery. I hope this will provide others with a fair comparison to aid in choosing a solution which best fits their needs.

Did you learn anything as you researched and wrote this article that you did not know before? I was at first surprised by how little of a difference there was in efficiency for a high duty-cycle example. There are some slight differences between the controllers which lead to this. One difference is the location of the current sense resistor. The synchronous solution still however, has the benefit of a smaller footprint. Overall, I was lucky to have the development go very smoothly, which doesn’t always happen on engineering projects. I enjoyed writing it and hope to write more when I come with additional ideas.

An excerpt from his article:

"Users of battery-operated applications desire the longest run time possible, and reducing the power loss can directly improve run time. Today it is well known that using a synchronous rectifier can reduce power loss and improve thermal capability. Designers of buck converters and controllers for stepdown applications are already employing this technique. Synchronous boost controllers also have been developed to address power efficiency in step-up applications.

Two typical boost applications can be used to demonstrate the difference between synchronous and nonsynchronous rectification. The first is a lower-input-voltage application that may operate at low duty cycles or, in other words, when the output voltage is close to the input voltage. Example inputs for this system are a USB port or a lithium-ion (Li-Ion) battery pack with two or three series cells. The DC/DC power supply steps up the voltage for charging a two-cell Li-Ion battery or the battery of a tablet PC. The other application boosts the voltage of a system power rail to a high output voltage that can operate at higher duty cycles where the output voltage is much higher than the input voltage. An example input is a 12-V power rail. The high output voltage may be needed for power amplifiers, industrial PCs, or pump-and-dump energy storage for higher energy density."

New book focuses on Battery Power

MattMcK — Tue, 21 May 2013 12:00:00 GMT

I sat down this week with Yevgen Barsukov and Jinrong Qian, two of TI’s leading battery technology experts to discuss the release of their new 240-page book, Battery Power Management for Portable Devices (by Artech House publishing -- available now on Amazon). The book provides comprehensive coverage of the latest battery management components and technology used in portable electronics, ranging from smartphones to ultrabooks and tablets and many other designs.

According to the authors, there is a growing need to educate battery pack makers and portable electronics manufacturers about the characteristics of batteries and battery chemistries.

“Over the last 10-12 years, we saw a large number of customers who tried to implement newer battery types and chemistries, from lead-acid to NiMH and NiCd and then higher-capacity lithium batteries,” said Qian, who is product line manager for TI’s battery chargers. It became really important to help clarify battery management concepts and outline the characteristics of different types of chemistries. Even though TI is the leading provider of power management integrated circuits, we have some of the best battery chemistry experts on staff.”

“We hope this book will be useful to a range of readers from engineering experts to students in related fields,” said Barsukov, IP development manager and chemist in the battery management systems group. “Our goal is to help them better understand power design techniques and battery characteristics – so that end consumers will ultimately experience portable electronics with long battery life, faster charging and safer batteries.”

Battery Power Management for Portable Devices discusses how to use new innovative charging circuits for faster and cooler charging; how to design with battery gauge technology that provide the longest possible run-time, while ensuring data protection; and utilize safety circuits that provide multiple independent levels of battery protection. The book provides real-world perspective of battery management systems, and covers:

Battery Chemistry Fundamentals and Characteristics
Battery Charger Techniques
Battery Safety and Protection
Cell-Balancing Techniques
Battery Fuel Gauging (state-of-charge and remaining run-time indication)
System Battery Power Management Solutions

The book already received a couple of notable reviews from other industry experts.

“This book provides valuable insights into why batteries behave the way they do so that you can understand how to use them in an optimal fashion. Recognized as industry experts, Jinrong and Yevgen have compiled a comprehensive set of information using their extensive experience in practical battery management. This book will certainly be perched on my desk, and I expect to refer to it often.” – Andy Keates, battery technologist at Intel Corporation. (As referenced in the Foreword of the book).

David Andrea, author of “Battery Management Systems for Large Lithium-Ion Battery Packs,” reviewed the book on his blog.

I hope my colleagues find great success with their first book!

Dave's Powertrip: Big Numbers, Big Confusion

Dave Freeman — Thu, 16 May 2013 17:26:00 GMT

It seems that big numbers carry with them big confusion. Big numbers from the age of the universe to the national debt can lead to interesting conversations at the lunch table. The magnitude of such numbers draws our attention, and the engineer in us leads us to make some use of these numbers. For example, the recently updated estimated age of the universe is 13.82 billion years, an increase of about a million years.¹ It is interesting that the reported value doesn’t even have 1 million as a significant digit in the reported age. The real point of the change is that the universe is expanding slower than originally thought.

In my last post, I talked about the power drain on my cell phone when comparing 3G to 4G networks. In April of this year, Centre for Energy-Efficient Telecommunications (CEET) published a report titled, “The Power of Wireless Cloud.”² This is an excellent report and quite easy reading. The report makes several interesting points and predictions. For example, the wireless cloud consumes about 9.2 TWh in 2012, and is expected to grow by 460% to 43 TWh by 2015. Another point is that only about 9% of the wireless cloud energy is consumed by data centers. With all the focus on data center energy efficiency, I would have thought that data centers are a far bigger energy hog.

An earlier report by Dr. Jonathan Koomey states that data centers consume between 1.1 to 1.5 percent of global electricity.³ This is a very large number. The World Bank estimates that the global production of electricity is about 21.49e12 kWh or 21,490 TWh.⁴ Even 1.1 percent is about 236 TWh. This is considerably more than estimated by CEET. So where is the confusion?

Figure 1. From smart phones to the cloud and the energy need.⁵

Alcatel-Lucent reported on the power and energy of worldwide base stations and their connected systems.⁵ This analysis shows that the big energy appetite comes from wireless base stations. Figure 1 shows that the estimated energy consumed annually by wireless base stations is about 60 TWh, while the server and related services consumed is about 14 TWh. This ratio is not quite what was reported by CEET. The Alcatel-Lucent report also addressed the power amplifier’s (PA) power efficiency, showing a range of efficiencies from 6 to 40%, depending on the output power.

Analog Applications Spotlight: Bosheng Sun

Heather Weir — Fri, 10 May 2013 22:36:00 GMT

I'm pleased to welcome Bosheng Sun to the Power House blog. Bosheng is the mind behind the article "Digital current balancing for an interleaved boost PFC" featured in TI's Analog Applications Journal newsletter.

Welcome Bosheng!

What is the problem/challenge you saw that spurred you to write the article “Digital current balancing for an interleaved boost PFC? As a Systems Engineer at TI, I had a customer using TI’s UCD3138 digital power management controller to design a 2-phase interleaved PFC. They needed current balancing between the two phases, but didn’t know how to do that. They asked me to help them, so I developed a digital current balancing algorithm for them that they liked. I thought there could be more customers who wanted to use the UCD3138 to design a 2-phase interleaved PFC, so I wrote an article to explain how to do PFC current balancing digitally. I also explain the advantages of TI’s UCD3138 for current balancing compared to other digital controllers. Hopefully, this article can help other design engineers out.

Dual current-control loops with UCD3138

What was the most difficult aspect of the topic you wrote about and why? There are analog PFC controllers on the market that can do current balancing, but I didn’t see any good digital methods particularly suited to TI’s UCD3138, and without any extra cost to do the job. The customer also was not very clear about their exact requirements. When I developed the first method, they didn’t like it. Then I tried a second method, they are still not happy. By the third try, I understood exactly what they wanted, and everybody was happy. Afterwards, I thought it would be a good idea to introduce the first two methods in an article so that people could see the pros and cons of each method, and learn from it, as I did.

What application do you think your article is best suited for? For any digital-controlled multi-phase PFC application.

Did you learn anything as you researched and wrote this article that you did not know before? Our team has been doing digital PFC for several years, but this is the first time we were asked for a current balancing feature. By working with the customer to create a solution, we now understand the differences between the different digital current balancing methods and can help others in the future.

An excerpt from his article:

"A power-factor correction (PFC) converter lets the input current track the input voltage so that the load appears like a resistor to the voltage source that powers it. The most popular power topology used in active PFC is the non-isolated boost converter. For high power levels, two boost units can connect to the same bridge rectifier and operate at 180° out of phase (Figure 1). This is called two-phase interleaved PFC. By controlling two phases’ inductor currents 180° out of phase, both input- and output-current ripple can be reduced. As a result, a smaller electromagnetic-interference filter can be used, which reduces material costs. Due to discrepancies between the two sets of components used in the two boost circuits, the two inductor currents inevitably will be different. This situation gets worse when PFC enters continuous-conduction mode (CCM). While the unbalanced current causes more thermal stress on one phase, it may also mistrigger over-current protection. Therefore, a current-balancing mechanism is necessary for the interleaved PFC design.1–4

This article discusses three different digital-control methods of balancing inductor currents. The first method senses the inductor current on each switching cycle, compares the current difference between the two phases, then adjusts the duty ratio of one phase cycle-by-cycle. The second method only adjusts the duty ratio in each half AC cycle. The third method uses two independent current loops to control each phase individually. Since these loops share the same current reference, the current is balanced automatically."

How to choose an LDO or switching regulator

Rich Nowakowski — Wed, 08 May 2013 21:17:00 GMT

I remember when I first started working with power management devices over 15 years ago. Quite frankly, I didn't even know what an ‘LDO’ was, or even a switching regulator for that matter, since those terms weren't covered in the electrical engineering courses I took. Because of that, I waited until the last minute to do the point-of-load power management design. It made sense to wait until I knew how much power I needed before I started the design, I figured.

Boy was I in for a few surprises!

Lucky for me, there weren't as many options as there are today. On the other hand, there weren't as many tools to help my design, either. After knowing the input voltage, output voltage, and output current for each rail, the solutions that were available seemed like a confusing collection of tools in a toolbox. I ended up using the LM317 linear regulator for most of my power rails since it was easy to use and the output currents were not that high.

Looking back, I could have done better (no offense to LM317 users!).

If I could go back in time with today’s toolbox, I would select the TPS54061, a wide input voltage, step-down DC/DC converter that is smaller in size by integrating both power FETs, it’s more efficient, and doesn't need as much copper on the board to dissipate heat… AND I wouldn't have the fear of magnetics anymore, since that was a tough class as I recall.

However, I learned over time that there is no right answer. It depends. Whether designing for low noise, high efficiency, small size, or a fast transient response, I learned that each tool, or part, has its own unique purpose. Each voltage level has a special consideration and may have a trade-off.

If you are new to designing with point-of-load power management devices, this Fundamentals of choosing LDO and switching regulators course will explain power trade-offs to help you choose the best solution. If you have done many power designs, you will learn about some new tools that can make designing your power architecture more quickly.

Other resources:

How to pick an LDO based on your application - Video

How to pick a Linear Regulator for Noise-Sensitive Applications - Analog applications journal (AAJ) article

Low-dropout regulators - quick reference guide

The Right LDO for your application - LDO's by applications webpage

Extend battery life in tablets with one chip

Pedro Artal — Thu, 02 May 2013 17:10:00 GMT

Until recently, the majority of the battery packs used to power tablets were configured with several cells in parallel. If we take the example of three cells in parallel, the output currents become significant. With the new approach of connecting the cells in series, currents stay in a reasonable level AND we achieve significant efficiency improvements. The diagram below compares both configurations.

During my visits with tablet customers around the world, I continue to see two key design requirements: a) design extremely thin tablets, and b) extend battery life. After a 12-month development time working with both lead customers and our design-team, we created the industry’s first single-chip, front-end power management unit (PMU) for tablets and other portable applications -- the TPS65090. By integrating 15 functions in a new package (multi-raw QFN), and supporting the increasingly popular 2-3 Li-Ion cells in series architecture, we solved the customers’ two key requirements.

This single-chip, front-end PMU integrates a 4-A switching PowerPath charger, three 5-A DC/DC step-down converters, seven load switches, two always-on LDOs and a 10-channel analog-to-digital converter (ADC). The new device integrates all front-end power functions required in any portable equipment, allowing customers to design ultra-slim and light devices.

2-3 cells in parallel: 30W = 4V x 7.5A

Disadvantages:

DC/DC boost from 4V to 38V below 85% efficiency.
Very high currents: 6A-8A. Larger copper traces.
Significant IR voltage-drop at input connections and PCB traces.

2-3 cells in series: 30W = 12V x 2.5A

Advantages:

Longer battery run-time as full voltage range of each cell can be utilized.
DC/DC boost from 12V to 38V in 95% efficiency range.
Acceptable currents (2A-3A) and PCB costs (smaller copper traces).

Additional resources:

Multimedia tablets system block diagrams
Solution guides: Tablet brochure and Power management units for embedded processors
TI PMU solutions

Dave's Powertrip: What does “access” really mean?

Dave Freeman — Tue, 30 Apr 2013 16:00:00 GMT

Intel Labs held their “Trendspotting Summit 2013” on April 2^nd this year. They invited World Bank Managing Director Caroline Anstey to speak.¹ Her speech content was something that is generally removed from what we discuss during our work days. She opened by stating that 43 percent of the population in Nigeria is under 16 years old. This takes some thinking to discover what this means to our industry. Her presentation focused on four key changes, and all four were interesting. However, the third change, “The Mobile Revolution,” got my attention although was it was the least elaborated on. I think it was the opening statement, “Today more people have access to a mobile phone than a toilet,” that caught my attention. At first this seems almost funny.

Studies have shown that 75 percent of Americans use their phones while in the bathroom.² So I guess this is overlapping access. OSHA recommends a minimum number of toilets per sex. For example, if you have between 111 and 150 employees of each sex, the facilities should have a minimum of six toilets for each sex.³ I know that in my workplace every one of those employees has a cellphone. So it is not surprising that most people will have more access to cell phones compared to a toilet. Anyway, this caused me to think about what it means to have access to a cell phone.

If you asked any one of my children what it means to have access to a cellphone, they would answer based on the cellphone being a smartphone. They very seldom use voice calls, basically only one of us parents ever calls them. So access is based on Internet connectivity, and the smartphone having the energy to maintain it.

We are back to a familiar issue, connectivity and the energy needed to maintain it. When the IPhone 5 was introduced, there was great expectation for connectivity time. For example, Apple indicated that the phone could provide up to eight hours of web browsing on the ATT LTE network. However, measurement by iLounge showed it was closer to six hours.⁴ The difference is more about having four full bars of LTE signal strength relative to only two or three bars. The lower signal strength is more typical of the user’s experience. Nonetheless, the users always think they should get the maximum hours of connected time.

To see what I actually have for battery life and connectivity, I decided to test my Android phone. I was only aware that my smartphone would need to be put back on the charger having started the day with a fully charged battery.

I configured my phone so that WiFi, GPS, and Bluetooth were turned off. I charged the phone to full, then removed the charger while the phone was in idle mode. After four hours, the battery was down to about 78 percent state-of-charge. Figure 1 (above) shows the power percentiles for the operating functions. An interesting thing to me was that Deep Sea was consuming power when the display was off. Deep Sea is the bubble background on the display and I would have thought it would have been placed in suspend if the display is off. The next consumer, Screen, was also strange in that the screen was off except for the brief time when I stopped the experiment and record the information. The last thing to note is that if you add up the percentiles you get 102 percent.

Read remaining article on EDN.com.

Power to the people! - Dave Freeman

References

Living in a Changing World: World Bank Managing Director Caroline Anstey's Speech, The World Bank, Intel Trendspotting Summit 2013, April 2, 2013.
IT in the Toilet: Study shows cell phones big in bathroom, by Amanda Kooser, CNET, February 1, 2012.
United States Department of Labor, Occupational Safety and Health Administration
iPhone 5 Battery Life Reduced Due to LTE Signal Strength, by Jim Tanous, The Mac Observer, September 27, 2012.

Fully Charged: The Path of Least Resistance

Upal Sengupta — Sat, 27 Apr 2013 14:30:00 GMT

Anyone who works in power conversion and battery management electronics knows that efficiency is important. Engineers measure efficiency on the lab bench, but an end user of a portable product experiences battery life and the surface temperature of the device. While someone may not notice a 5% or 10% difference in battery life over a period of several hours, he or she could certainly sense an additional 5 or 10 degrees of heat on the outer surface of their handheld device.

As smartphones, tablets and portable instruments add more sophisticated features and bigger, brighter displays, they require higher capacity batteries – and correspondingly more power to charge quickly. The tight packaging of handheld products means that the heat generated on a PC board often finds its way to the exterior case of the device. Furthermore, many studies have shown that Lithium-Ion batteries suffer capacity degradation over time when exposed to high temperatures. So low efficiency is not just bad for the battery run-time on an individual cycle, but bad for long term service life of the battery, as well as an end user’s perception of the product quality. Using a high efficiency battery charger with low-resistance power FETs is one of the best ways to minimize heat generation in a portable system and keep your battery cool.

For the rest of the post, see Upal's Fully Charged blog on Battery Power Online here: http://www.batterypoweronline.com/main/blogs/the-path-of-least-resistance/#more-4324.

Testing power supply: Measuring stability

Bob Hanrahan — Wed, 24 Apr 2013 00:59:00 GMT

Previously, I posted part 1 and 2 of a 3 part series on how to test your power supply design: measuring efficiency (part 1) and measuring noise (part 2). I covered various noise sources and how to properly measure them with an oscilloscope. I also discussed output errors created by line and load transients

Today, I'll touch on the third and final metric when testing power supply: measuring stability.

A power supply is a closed loop amplifier; it takes in electrical energy and converts it to electrical energy in another form, at a specific regulated voltage and/or current. Power supplies regulate by sensing the output and comparing a portion of it to a reference voltage. The difference between the sense signal and the reference is amplified and then used to control the power stage of the regulator to keep the voltage (or current) constant (Figure 1).

Power supplies employ negative feedback from the output back to an error amplifier to ensure proper regulation over various operating conditions (load changes, temp changes, input voltage changes, etc.). As with any stable closed-loop system, one must ensure the closed-loop gain is less than one at frequencies of operation or risk oscillation and/or other non-desirable characteristics. The negative feedback term of a power supply must be sufficiently out of phase with the input or establish a gain of less than one to ensure proper operation.

A typical regulator IC provides the necessary phase margin within the device to ensure stable operation. Like any engineer, an IC designer works with operating limit assumptions and often provides control mechanisms to adjust the internal phase delay to accommodate for various load extremes. A regulator might be designed to provide 90 degrees of phase margin with a nominal output impedance yet if the impedance is more capacitive than anticipated the phase delay might grow to a point to where the phase being fed back from the power supply output is in phase with the internal feedback point. The reversal in phase creates positive feedback with a gain of more than one, the formula for an oscillator. We all know that this is not desirable within a voltage regulator circuit.

Many regulators provide a mechanism to adjust the internal phase delay, usually accomplished with an external compensation network employing a few passive components. In some cases the regulator does not provide such hooks and must be employed within defined operating extremes (min/max output impedance over load extremes). In any case one must be able to properly analyze a circuit to determine if design adjustments are necessary. While loop characteristics can be simulated, real world system level characteristics such as PCB and connector impedances are difficult to accurately model, especially with lower cost simulation tools. So an actual stability measurement is necessary to understand actual loop stability.

Yes, I have seen many situations where a system was released to production and later in production became unstable based on environmental changes and/or operating extremes. In these situations the prototype likely worked fine yet phase and gain margins within the power supply where were not testing during prototype test. If stability of a power supply is tested a designer identifies the problem and corrects the issue before it causes more costly production issues.

Read in more detail how to measure noise in a power supply in my full article on EDN.

Walk through how to measure noise in your power supply with me in this Engineer It video.

If you have any questions or comments on how to measure stability, please leave them in the comments section below.

Good luck!

Testing power supply: Measuring Noise

Bob Hanrahan — Sat, 20 Apr 2013 14:00:00 GMT

Last week, I posted part 1 of a 3 part series on how to test your power supply design: Testing power supply: measuring efficiency. I covered the fundamentals about testing, including the necessary equipment and how to prepare a circuit for testing. I also covered how to accurately measure start-up time, current limit, and power supply efficiency.

Today, I'll touch on another important metric when it comes to testing power supply performance: measuring noise.

What causes power supply noise?

Power supply noise is generated from many different sources. Like any amplifier, power supplies generate many different types of noise, but a switch mode design also has to deal with the noise generated by the inherent switching noise which takes place. A switching power supply can be designed to minimize its switching noise and can include output filters to reduce the noise, but it's impossible to know exactly what levels of noise a power supply will produce until it's actually measured.

Transient Ripple Noise

Why should one measure noise?

The bias voltages within any system are what I like to think of as the foundation of the electrical circuits. All of the system connects to these sources of power and must deal with its associated noise. If the noise generated (or passed) from the power supply is beyond what a circuit can tolerate, a system will naturally malfunction. The issue with noise is that it might be such that it doesn't cause catastrophic failure, at least not all the time. Noise sometimes causes intermittent errors which might not be evident during a thorough system test in a specific environment with a typical set of component values, but might later cause problems. In some cases, I see software patches written to “cover-up” occasional system errors which may be found to root themselves back to power supply noise. Is software the right way to fix a problem which could have been addressed within the power supply? I think not, but I best not digress into what might be a somewhat philosophical discussion, better I add that to the list of discussions for later, “Fixing Problems, Software vs Hardware”…

I occasionally see noisy power supply designs causing a system to fail EMI testing, slowing down a product release. These slowdowns may be avoided if proper testing was performed and noise issues dealt with earlier in the process. When it comes to biasing an analog circuit, power supply noise can result in a lower performance system, possibly reducing the products value to the end customer. Think about the power supply for an analog signal path from a sensor of some sort. In these systems noise directly impacts the sensitivity of the system, a higher noise floor results in lower sensitivity. When a designer takes the time to actually measure and analyze the noise generated by a power supply they can either accept the performance or almost always make modifications to avoid later system level problems, often at almost no extra cost. The cost to test and possibly modify a power supply is usually far less then later system level debug and modifications, or the unfortunate situation when a product is released with sub-par performance.

It’s this attention to detail that makes the difference between a marginally working product, and a highest performance, highest reliability product.

Read in more detail how to measure noise in a power supply in my full article on EDN.

Walk through how to measure noise in your power supply with me in this Engineer It video.

Part 3 on how to measure stability, coming soon.

If you have any questions or comments on how to measure noise, please leave them in the comment section below.

Happy testing!

Texas Instruments brings WEBENCH® speed training to DESIGN West!

Jeff Perry - WEBENCH Design Center — Wed, 10 Apr 2013 22:01:00 GMT

Have you finished your PCB design but still need to power it? Are you confident your design features the best mix of performance and cost? If you've been in this situation, I've got a free class for you!

Texas Instruments will host a special “speed training” session, "Play the game - with WEBENCH," at the DESIGN West conference at the San Jose Convention Center on April 22-25, where you will learn how to create a power supply design in just a few minutes. You will discover how to fine-tune your design to get the best balance of footprint, efficiency and cost. Then, you will choose from dozens of optimized solutions to select the best design for your needs.

You can find me here:

The infamous widget we will be playing with:

At the training, you’ll be provided with a laptop to practice your new skills, and you can join your comrades to participate in a competition to see who can zero in on the best design to win a prize. From what I've seen in the 13 years I've been involved with power supply design, I promise this will be the quickest way to get the design you need.

A little about me: As part of the WEBENCH team formed at the height of the Internet craze in 1999, I led the initial start up of the WEBENCH Designer tools, and I've been involved with it ever since. I've really enjoyed being part of an innovative team that leads the industry with a number of “firsts” including online circuit design, simulation and prototyping capabilities. I'm passionate about TI’s WEBENCH tools because they have helped engineers around the world be more efficient in their jobs. Please join me on April 25 at either the 12 p.m. or 1 p.m. session held on the DESIGN West conference exhibit floor. Sign up for the session here.

This is me:

See you there!

Testing power supply: Measuring efficiency

Bob Hanrahan — Mon, 08 Apr 2013 17:04:00 GMT

During my normal activity as an Analog Field Applications Engineer, I am called to help a customer solve system problems. These system problems sometimes relate back to the power supply. Last year, over a period of 3 months, I had 3 different situations at different customers where the root cause of a system problem was a relatively straight forward power supply design problem. Systems were in production, but problems were arising based on intermittent field failures. In each case, I discovered that the power supply needed a minor design change which could have easily been identified and implemented before the system was released to production.

What I found most interesting was that because of our advancement in software design tools, customers are placing much more trust in power supply designs without performing what used to be fairly standard bench testing. In cases, I observed system designers used the results from simulations tools as a strong indication of the robustness of a design, thus not placing as much time (if any at all) on actual bench testing of the power supply. This observation, with the fact that many designers have never gained experience with bench testing, left me with the clear realization that an article was needed on the subject. I sometimes wonder how much of this relates back to the current de-emphasis on hands-on design and test in universities, where software tools are replacing these tasks… but that is a topic for a future blog.

That being said, why is testing power supply so important?

As explained above, if a power supply is not fully tested it may leave a system in a marginal state of operation. A marginal design can result in system failures once the system is deployed and operating in different environments. System components vary slightly over time which can result in failures of a system that was not fully tested and/or analyzed.

Here is a simple procedure for accurately measuring efficiency:

Before connecting the DC power supply to your power circuit, set the proper input voltage and verify correct polarity.
Connect a voltmeter to the input and output of the power supply close to the input and output connectors.
Connect a current meter to the input and output, see earlier comments.
Connect the electronic load to the output and set it to the lowest value of interest.
Turn on the input voltage and set it to provide exactly the nominal input voltage across the power supply input. Important: Input voltage accuracy may need to be within a few millivolts to ensure overall accuracy and needs to be adjusted after each time the load is changed.
Record the input and output current along with the output voltage. The input voltage is fixed by step 5.
Increase the load at regular intervals up to a load at or above 100 percent. Testing up to 110 percent of maximum load or greater is valuable to help understand operating margins.
Plot curves of the output power over the input power (*100) to show the peak efficiency and efficiency at different loads (Figure 3)

Find more detail on how to measure efficiency of a power supply in my full article on EDN.

You can walk through the process with me in this Engineer It video on how to measure efficiency of a power supply:

Part 2 on measuring noise, and part 3 on measuring stability coming soon.

Why do you think fewer designers are testing their power supply?

Dave's Powertrip #15: Science or Engineering Fair?

Dave Freeman — Tue, 02 Apr 2013 21:14:00 GMT

My technical community service is now complete! I just finished judging the Science and Engineering Fair for the Plano Independent School District (PISD), Plano, Texas. Each year I look forward to this and find it exciting to interview the future scientists and engineers of America and, indeed, the World. The PISD holds the district fair as a tune-up for the regional fair. Every project in the district fair is already slated for the regional fair, but this gives the students a chance to practice in front of judges. My experience is that this level of commitment is not widespread, although it should be.

In my day, I entered the science fair only once when I was in the fifth grade. The school decided to have a fifth-grade-only science fair and the judge was our music/science teacher. Using an electromagnet powered by a 6V lantern battery, I demonstrated how the number of turns of wire on an electromagnet determined the amount of weight it could lift. As cool as it was, I lost to a volcano built of modeling clay, surrounded by giant over-sized plastic dinosaurs that nearly dwarfed the volcano. They did not even use baking soda and vinegar to mimic an active volcano. Our science teacher liked it because it was “so well done.” While that was science fair for me, today’s potential engineers have a much better venue.

This year I was given the junior division’s “Earth and Planetary” category to judge. There were only three projects for grades six through eight, so I also judged the senior division for grades nine through 12. My judging recruits were assigned “Energy and Transportation,” which delivered upwards of 20 projects, just in the junior division alone!

Many school districts use the 17 categories defined by the Intel International Science and Engineering Fair (ISEF)¹ (Table 1). These categories give students plenty of opportunity to choose unique projects. Some students choose categories that may have only a few other entries, like Earth and Planetary Science. Others choose categories “of the day” with many entries, like Energy and Transportation. This year the students I judged did not seem to know in which category they would be placed until the science fair opened.

Five projects were done really well, so judging the grand prize was tough. My favorite involved planarian. These flat worms, bisected in various ways, were subjected to an aloe vera-based product. The regrowth of non-exposed planarian versus the aloe group showed that the aloe group recovered faster. This is not the first science project to do this, but for a middle schooler, it was well done. And, after all, it did deal with flat worms!There were a couple of surprises in this year’s fair. The first is the number of projects that used a smartphone as a scientific instrument. One student did a project on “sonic crystals.” They constructed a structure of plastic tubing they hypothesized would either amplify or interfere with sound propagation. They used an iPhone and the appropriate application to produce a spectrum of sound. The sound was recorded with and without the crystal between the source and the receiver. The recorded sound was then analyzed to find any spectral deviation. Another student used the iPhone to measure ambient light by photographing a white sheet of paper in various lighting environments. In numerous projects smartphones were used to make movies to better communicate their scientific procedures.

Another surprise was the grand prize winner. The project was to build a hydrogen fuel cell to power a gaming controller. It was no surprise that this could be done. But again, it was the engineering effort and learning by the middle schooler that attracted the judges.

Read remaining article on EDN.com.

Power to the people! - Dave Freeman

Developing and mentoring our technical talent is part of our commitment to our industry. What are your thoughts or experiences with student science and engineering projects? Or what are you doing differently to help instill in our youth the value of being an engineer?

References

1. "Intel ISEF Categories and Subcategories" www.societyforscience.org/isef/project_categories

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"Good Vibrations"

Upal Sengupta — Tue, 26 Mar 2013 15:34:00 GMT

I've always found "resonance" to be an interesting word, even when I couldn't always provide an accurate definition of it. There are so many different meanings, most of which have some connection to each other. As an electrical engineer, my first reaction at hearing the word now is to think of a tuned LC circuit... however there are a lot of other thoughts that follow. A pendulum, a playground swing-set, or a tuning fork can all provide examples of resonance in the physical world. I’ve asked others what resonance means to them and gotten a variety of responses from blank stares to “it reminds me of poetry.”

So what does resonance have to do with battery management? Resonant power converters are at the core of the wireless power technology that will improve the utility and usefulness of many battery-powered devices. As we become more and more dependent on these devices for everything we do on a daily basis, we need a means to keep them charged up and ready to use as much as possible.

To read the complete article, click on the following link:

http://www.batterypoweronline.com/main/blogs/good-vibrations/

Engineer It Video Series: Testing Power Supplies

Aimee — Tue, 26 Mar 2013 14:30:00 GMT

Let's talk about it! The Engineer It videos from Texas Instruments are instructional, how-to videos on a variety of technical topics. We've devoted this space to talk about a series of Engineer It videos devoted to testing power supplies. The four-part video series featuring TI's Bob Hanrahan describes how to properly test a DC/DC power supply, and ensure that it works reliably over various operating conditions. This series is intended to provide the designer with a sufficient understanding about the testing needed to verify a reliable power supply design. Share your thoughts and questions here. <hr /> Engineer It: Testing Power Supplies with Bob Hanrahan Part 1: Overview <img style="visibility: hidden; width: 0px; height: 0px;" border="0" width="0" height="0" src="http://c.gigcount.com/wildfire/IMP/CXNID=2000002.11NXC/bT*xJmx*PTEzNjQ5Mzk3MTQxMDEmcHQ9MTM2NDkzOTg2NzI5MSZwPSZkPSZnPTImbz*4MjZlMDBmYzVhZTA*ZmY*OGI1OTYwZDQ3/NzJmYWE5NiZvZj*w.gif" /><object name="kaltura_player_1364939711" id="kaltura_player_1364939711" type="application/x-shockwave-flash" allowscriptaccess="always" allownetworking="all" allowfullscreen="true" height="330" width="400" data="http://www.kaltura.com/index.php/kwidget/wid/0_06cjn733/uiconf_id/2342281"><param name="allowScriptAccess" value="always" /><param name="allowNetworking" value="all" /><param name="allowFullScreen" value="true" /><param name="bgcolor" value="#000000" /><param name="movie" value="http://www.kaltura.com/index.php/kwidget/wid/0_06cjn733/uiconf_id/2342281" /><param name="flashVars" value="" /><a href="http://corp.kaltura.com">video platform</a><a href="http://corp.kaltura.com/video_platform/video_management">video management</a><a href="http://corp.kaltura.com/solutions/video_solution">video solutions</a><a href="http://corp.kaltura.com/video_platform/video_publishing">video player</a></object> Part 2: Measuring Efficiency <img style="visibility: hidden; width: 0px; height: 0px;" border="0" width="0" height="0" src="http://c.gigcount.com/wildfire/IMP/CXNID=2000002.11NXC/bT*xJmx*PTEzNjQ4NDY1MjI1MTAmcHQ9MTM2NDg*NjUyNDYyNiZwPSZkPSZnPTImbz*4MjZlMDBmYzVhZTA*ZmY*OGI1OTYwZDQ3/NzJmYWE5NiZvZj*w.gif" /><object name="kaltura_player_1364846522" id="kaltura_player_1364846522" type="application/x-shockwave-flash" allowscriptaccess="always" allownetworking="all" allowfullscreen="true" height="330" width="400" data="http://www.kaltura.com/index.php/kwidget/wid/0_lnzcq85b/uiconf_id/2342281"><param name="allowScriptAccess" value="always" /><param name="allowNetworking" value="all" /><param name="allowFullScreen" value="true" /><param name="bgcolor" value="#000000" /><param name="movie" value="http://www.kaltura.com/index.php/kwidget/wid/0_lnzcq85b/uiconf_id/2342281" /><param name="flashVars" value="" /><a href="http://corp.kaltura.com">video platform</a><a href="http://corp.kaltura.com/video_platform/video_management">video management</a><a href="http://corp.kaltura.com/solutions/video_solution">video solutions</a><a href="http://corp.kaltura.com/video_platform/video_publishing">video player</a></object> Part 3: Measuring Noise <img style="visibility: hidden; width: 0px; height: 0px;" border="0" width="0" height="0" src="http://c.gigcount.com/wildfire/IMP/CXNID=2000002.11NXC/bT*xJmx*PTEzNjQ4NDY1OTU*MzAmcHQ9MTM2NDg*NjU5NzQwMiZwPSZkPSZnPTImbz*4MjZlMDBmYzVhZTA*ZmY*OGI1OTYwZDQ3/NzJmYWE5NiZvZj*w.gif" /><object name="kaltura_player_1364846594" id="kaltura_player_1364846594" type="application/x-shockwave-flash" allowscriptaccess="always" allownetworking="all" allowfullscreen="true" height="330" width="400" data="http://www.kaltura.com/index.php/kwidget/wid/0_r10rojip/uiconf_id/2342281"><param name="allowScriptAccess" value="always" /><param name="allowNetworking" value="all" /><param name="allowFullScreen" value="true" /><param name="bgcolor" value="#000000" /><param name="movie" value="http://www.kaltura.com/index.php/kwidget/wid/0_r10rojip/uiconf_id/2342281" /><param name="flashVars" value="" /><a href="http://corp.kaltura.com">video platform</a><a href="http://corp.kaltura.com/video_platform/video_management">video management</a><a href="http://corp.kaltura.com/solutions/video_solution">video solutions</a><a href="http://corp.kaltura.com/video_platform/video_publishing">video player</a></object> Part 4: Measuring Stability <img style="visibility: hidden; width: 0px; height: 0px;" border="0" width="0" height="0" src="http://c.gigcount.com/wildfire/IMP/CXNID=2000002.11NXC/bT*xJmx*PTEzNjQ4NDY2NjkyNzkmcHQ9MTM2NDg*NjY3MTQ1NiZwPSZkPSZnPTImbz*4MjZlMDBmYzVhZTA*ZmY*OGI1OTYwZDQ3/NzJmYWE5NiZvZj*w.gif" /><object name="kaltura_player_1364846668" id="kaltura_player_1364846668" type="application/x-shockwave-flash" allowscriptaccess="always" allownetworking="all" allowfullscreen="true" height="330" width="400" data="http://www.kaltura.com/index.php/kwidget/wid/0_fq70e69n/uiconf_id/2342281"><param name="allowScriptAccess" value="always" /><param name="allowNetworking" value="all" /><param name="allowFullScreen" value="true" /><param name="bgcolor" value="#000000" /><param name="movie" value="http://www.kaltura.com/index.php/kwidget/wid/0_fq70e69n/uiconf_id/2342281" /><param name="flashVars" value="" /><a href="http://corp.kaltura.com">video platform</a><a href="http://corp.kaltura.com/video_platform/video_management">video management</a><a href="http://corp.kaltura.com/solutions/video_solution">video solutions</a><a href="http://corp.kaltura.com/video_platform/video_publishing">video player</a></object> Were these videos helpful? Do you have further questions? Is there additional material on this topic you would like to see covered?  Let's talk about it!