Category Archives: Circuit Analysis

A Must-Have Book for Every Test Engineer

MediumTestEngineersBookCoverThe Test Engineer’s Measurement Handbook / How to Design Tests for 1st-Pass Success
by Van Brollini

Van Brollini’s new book is an essential addition to the test engineer’s library, as well as the library of any product manager.

The Handbook contains practical advice that is based on Mr. Brollini’s extensive experience with test development, including unique insights that I have not seen elsewhere, insights that will provide the test engineer with a quantum leap in productivity.

The test engineer will also appreciate the fact that Brollini’s methods — clearly presented as a series of rules, tips, and straightforward equations — are practical and cost-effective, illustrated by real-world examples throughout.

The Handbook’s teachings can be applied with basic math and spreadsheet tools, although Brollini does recommend Design Master™ for best efficiency, particularly for more advanced applications.

(I have known Van for many years, as he was one of the first engineers to adopt our Design Master software. From time to time he has offered suggestions for improvements, which were incorporated into the software.)

The Test Engineer’s Measurement Handbook is available through the DACI website.

-Ed Walker

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Want To Learn Proper Worst Case Analysis Basics? See Our Latest Article at How2Power.com

A new Design Master article,  “Use Worst-Case Analysis Tool To Efficiently Validate Your Designs,” is now available in the latest issue of How2Power.com.

Free WCA Software: Design Master Lite Cloud Version

Design MasterTM, the practical and easy-to-use advanced worst case analysis software used worldwide, provides a fully integrated set of analysis tools, including worst case solutions to design equations, probability estimates of any out-of-spec conditions, sensitivities, and optimized values for design centering.

The Lite version is now available for free at How2Power.com, under Design Notes and Tools / Worst case analysis software. Although the Lite version has some functional restrictions, it is ideal for small projects and academic use. (For the full featured versions, please click here.)

Also, please be sure to watch for How2Power’s July Newsletter, which will include the application note, “How To Use Design Master for WCA – A Simple Example,” as well as other in-depth design articles for power electronics engineers.

Is Your Circuit Simulator Just A Pretty Face? Five Reasons Why Simulations Are Not Sufficient For Design Validation

Jerry Twomey recently pointed out some pitfalls with math-based circuit analysis (“Academic Simplifications Produce Meaningless Equations,” 13 June 2012, Electronic Design.com.)

I agree with the general sentiments of Mr. Twomey, but would like to point out that there is a simple solution to avoiding the pitfalls he mentions: develop equations from component data sheets, not from academic simplifications. This is straightforward and will be discussed further in a future post.

Also, it should be noted that simulations are not some miracle cure-all elixir. Indeed, simulators are also math-based creatures: SPICE and its cousins simply grind out numerical solutions to the multitude of hidden equations that are buried beneath their pretty graphical interfaces.

So what’s the problem with simulators? A lot. For example,

1. Because simulator math is hidden behind the user interface, simulators don’t promote engineering analysis (thinking). To the contrary, they promote lazy tweak-and-tune tinkering.

2. Because simulator component models are typically very complex, the interactions between important variables are usually obscure, if not downright unfathomable. Obscurity does not promote engineering understanding.

3. Simulator results typically do not provide insight into important sensitivities. For example, can your simulator tell you how sensitive your power supply’s thermal stability is to the Rds(on) of the switching Mosfet, including the effects of thermal feedback?

4. A simulation “run” is not an analysis, but is instead a virtual prototype test. Yes, it’s better to check out crappy designs with a simulator rather than wasting time and money on building and testing crappy hardware. So simulators have their place, particularly when checking out initial design concepts. Eventually, however, hardware testing is required to verify that the simulator models were correct. And you will still need to do a worst case math analysis to determine performance limits, and to confirm that desired performance will be maintained in the presence of tolerances and aging.

  • Proper Design Validation = Testing/Simulations + Analysis.

5. Simulators don’t really do worst case analysis. Yes, you can use a simulator to implement a bunch of Monte Carlo runs, but valid results requires (a) identification of all of the important parameters (such as Rds(on)), (b) assignment of the appropriate distributions to those parameters (such distributions are typically not available), and (c) the generation of enough runs to catch errors out in the tails of the overall resultant distribution (and how many runs should you do? Hmmm…).

  • Monte Carlo is not a crystal ball. It only shows you the production performance you will get if all of your assumptions were correct, and if you did enough runs.
  • The knowledge required to determine the number of runs requires an exhaustive study of the circuit’s parameters, distributions, and interrelationships (not practical), or a knowledge of the limits of performance.
  • But if you know the limits of performance, then why do you need a Monte Carlo analysis? You don’t. You can skip it altogether and go directly to a math-based Worst Case Analysis.

For further insights into math-based Worst Case Analysis versus simulations, please see “Design MasterTM: A Straightforward No-Nonsense Approach to Design Validation.”

-Ed Walker

Bulletin: Design Master Analyzer Now Available

The Design Master™ Analyzer (DMA) is a simple fill-in-the-blanks quick and easy worst case analysis tool. DMA is based on expert templates, allowing powerful results to be quickly generated by less experienced engineers.

DMA is designed to be more easily used by iPad and other compact devices.

The Design Master Analyzer is targeted at specific applications with a very simple and easy-to-use format. If you’re an engineering director or project manager, simply provide copies of specific DMA applications to your staff for quick and efficient “fill in the blanks” analyses and receive design validation in minutes rather than weeks.

Although DMA files are useable as provided and are securely locked, a Professional Edition “master” owner can edit or create DMA templates. The DMA engine can also be used to convert any existing Design Master file into a DMA fill-in-the-blanks format. Please inquire for pricing for the DMA engine.

To order please click here.

Oh, No! We Forgot the Bozo Protection (and other Persistent Design Errors)

We’ve contributed to hundreds of electronics design projects wherein the circuitry was subjected to rigorous WCA+ (WCA+ is our advanced version of Worst Case Analysis; see “Four Costly Myths About WCA“). Our analyses invariably detected various design deficiencies, both stress and functional. Unfortunately, like an annoying relative who can’t get the hint to please not visit again, some common problems that we were finding decades ago are still regularly popping up in today’s new designs. These include:

  • Lack of protection from Bozo the Clown: inadequate ESD protection; connectors without reverse-polarity keying; identical connectors for all ports (you don’t expect Bozo to pay any attention to cable labels or connector colors, do you?); no spills/immersion protection (e.g., coffee, slurpees, beer, or even juice from a steak being thawed on top of a warm electronics unit (no kidding)).
  • Transient protection devices (TPDs) not present at circuit interfaces. Not just the AC power and load interfaces, but all the internal interfaces that are exposed to ESD or potentially unruly test equipment during testing, particularly for costly subassemblies. We’ve seen a hugely expensive and schedule-critical board blown up by a test instrument failure; a disaster that could have been prevented by a few bucks’ worth of TPDs.
  • Failure to account for dissimilar power supply voltages, causing interface overdrive and/or latchup. (Sometimes this only occurs during transient conditions, making the deficiency hard to catch during testing. You will typically learn about it after you’ve shipped a few thousand units and your boss is frantically paging you to get back to work after you’ve had too many beers and the last thing you want is to work through the night and the weekend on warranty repairs while angry customers are screaming at you on the phone…but I digress…)
  • Inadequate ratings for AC mains rectifiers and other power components, particularly in switchmode supplies. Hint: Don’t completely rely on SPICE or other simulations to identify realistic worst case performance boundaries for these components. Or do, but then be sure to not provide a warranty with your product.

For some more tips, see page 210 of The Design Analysis Handbook; still very relevant after all of these years. (Note: We’re out of copies of the Revised Edition, but it’s still available from Amazon and Elsevier.)

P.S. We’re considering creating some low-cost mini-modules of our Design Master WCA+ software, configured for common design tasks such as proper TPD selection, op amp gain stage analysis, etc. (If you care to comment, your feedback will be appreciated and will help us make a decision. You can add a comment to this post, or email us at daci@daci-wca.com.)

Thanks.
-Ed Walker

Toyota Sudden Acceleration: An Example Of How Not To Do A Failure Analysis

P.S. IF YOU’RE DRIVING A TOYOTA, TURN OFF THE CRUISE CONTROL
(see “Toyota Sudden Acceleration Document Withheld From Feds: CNN” by Sharon Silke Carty in the 03/02/12 Huffington Post)

At a crime scene, everyone knows: don’t move the body! Investigators of electronics failures should follow the same rule.

Valuable evidence may be contained in interconnected subassemblies that are initially assumed to be “innocent.” Disconnecting cables, unplugging circuits cards, and other disturbances can cause irretrievable loss of data.

Example: After its investigation of Toyota “sudden acceleration” incidents, the National Highway Traffic Safety Administration (as well as Toyota) claimed that the electronics were not at fault. Yet the NHTSA based its conclusions, at least in part, on a postmortem that was performed on a dismantled vehicle, thereby disturbing the accelerator system’s linkages with the cruise control system.

(For an earlier comment on this issue from our Engineering Thinking blog, please see “Toyota Unintended Acceleration: ‘No Electronics-Based Cause’: Not True & Misleading“)

4th Qtr 2011

(c) 2011 Design/Analysis Consultants, Inc.
Newsletter content may be copied in whole or part if attribution
to DACI and any referenced source is prominently displayed with the copied material

This Issue: NEWS BITE: Rising Sun Gets Snagged On Mountain And Breaks Apart! / DESIGN MASTER TIP: Minimizing Calculation Time / ANALYSIS: Why Do A Worst Case Analysis? / TECH TIP: Nice Overview of Considerations for External Components for Switching Regulators / MORE UNINTENDED CONSEQUENCES: Wind Power Kills Endangered Species / ANALYSIS QUIZ: Adjustable 3-Terminal Regulator Output Tolerance

NEWS BITE: Rising Sun Gets Snagged On Mountain And Breaks Apart!
Motorists cautioned to avoid area due to high temperatures.

First planet with two suns reported found
15 Sep 2011, NASA and World Science

DESIGN MASTER™ TIP: Minimizing Calculation Time

Do an initial run and check sensitivities. Thereafter set the variables to their respective worst case values to reduce calc time until the design is finalized. Then set the variables back to their full range for a final calculation to obtain probabilities for risk assessment.

ANALYSIS: Why Do A Worst Case Analysis?

 
TECH TIP: Nice Overview of Considerations for External Components for Switching Regulators
See “Power System Performance Requires The Right Actives And Passives” by Tim Watkins, 8 Sep 2011 Electronic Design

MORE UNINTENDED CONSEQUENCES: Wind Power Kills Endangered Species

In the Bay Area, when activists in the 1980s demanded a cleaner planet, the state responded with the Altamont Pass Wind Resource Area. The state-approved wind farm, built with federal tax credits, kills 4,700 birds annually, including 1,300 raptors, among them 70 golden eagles…

“There’s a big, big hypocrisy here,” Sue Hammer of Tehachapi Wildlife Rehab in Kern County said. “If I shoot an eagle, it’s a $10,000 fine and/or a vacation of one to five years in a federal pen of my choice.”

From “Energy in America: Dead Birds Unintended Consequence of Wind Power Development” by William La Jeunesse, 16 Aug 2011, FoxNews.com

ANALYSIS QUIZ: Adjustable 3-Terminal Regulator Output Tolerance

An LM317T regulator with 36V input is set for 24V nominal output, using 1/8W 1% 100ppm thick film resistors (10K and 549 ohms). The regulator must deliver 1A and operate from 0 to 50 C for 10,000 hours.


Q: What will be the approximate worst case output tolerance? (Answer will be posted in the next newsletter.)

3rd Qtr 2011

(c) 2011 Design/Analysis Consultants, Inc.
Newsletter content may be copied in whole or part if attribution
to DACI and any referenced source is prominently displayed with the copied material

This Issue: NEWS BITE: Mutant Singing Cantaloup Wins Karaoke Contest! / MORE UNINTENDED CONSEQUENCES: Hands-Free Faucets / DESIGN MASTER TIP: AC Rectifier Worst Case Analysis Made Easy / ART MEETS ENGINEERING: The Invisible Man / STATISTICAL DESIGN PITFALLS: Monte Carlo Is Not Worst Case Analysis

NEWS BITE: Mutant Singing Cantaloup Wins Karaoke Contest!

Freaky Robot Mouth Learns to Sing,”
Evan Ackerman, 13 July 2011, IEEE Spectrum

MORE UNINTENDED CONSEQUENCES: Hands-Free Faucets Harbor More Germs Than Standard Faucets

Details here.

DESIGN MASTER TIP: AC Rectifier Circuit Worst Case Analysis Made Easy

In our previous Newsletter we provided a pretty good estimate for the ripple current for the bulk capacitor in an AC rectifier circuit. But what if you have a large volume product and you need a full worst case analysis to ensure high reliability, but one that is not overly pessimistic so that you can minimize cost? Design Master can help you achieve that optimum balance.

As readers are aware, we’ve started to release some DMeXpert “fill in the blank” WCA templates to make the design engineer’s life a bit easier. One of these is our AC Bridge Rectifier Analysis (ACBR1 $19) which allows the designer to determine all of the worst case component stresses within a minute or two. The analysis includes the effects of source impedance Rs (such as transformer secondary winding ohms), which if present can be used to reduce capacitor ripple current requirements, hence reduce capacitor cost.

As those who have studied AC rectifier circuits are aware, this seemingly simple circuit has resisted for decades all of the attempts to generate a single-formula solution, until recently, which we’ve included in ACBR1. Based on Keng Wu’s article, “Analyzing Full-Wave Rectifiers With Capacitor Filters” (1 Jan 2010, Power Electronics Technology), Wu’s formula allows a straightforward circuit solution, greatly reducing computational time. So with ACBR1 you can just fill in the blanks, click Calculate, and let Design Master do the rest.

ART MEETS ENGINEERING: The Invisible Man

Engineers who work for the military are sometimes required to design clothing, equipment, or even entire shelters to be “invisible” to various detection means. Chinese artist Liu Bolin has a gift for applying such camouflage in a non-technological way, as seen below. Hint: If you can’t spot Liu, look for his shoes first.

From “The Invisible Man: Dragon Series,” Vurdlak, 28 June 2011, http://www.moillusions.com

Some more fascinating photos here and here.

STATISTICAL DESIGN PITFALLS: Monte Carlo Is Not Worst Case Analysis

A lot of folks like to let a simulator crank out “worst case” results, using Monte Carlo statistical methods. But as we’ve explained previously (“Design Master vs Extreme Value, RSS, Monte Carlo, & Simulation,” and “Design Master vs Monte Carlo“), this can be not only time consuming, but risky. For example, Monte Carlo can easily miss small but significant errors (see example below). In addition, if the Monte Carlo runs are improperly implemented (such as including temperature or other dynamic variables) you will likely obtain wildly inaccurate results.

The Design Master Advantage

Instead of statistical sampling, Design Master uses a top-down approach to achieve safer and more cost-effective results, by (a) detecting the extreme limits of performance, and then (b) using a proprietary probability algorithm to estimate how often those results will exceed the specification limits.

EXAMPLE

Design Master results at 2 samples/variable versus
Monte Carlo at 10,000 samples/variable, for the gain of an 8-variable filter

As can be seen, the Monte Carlo analysis detected a minimum of 8.42 versus the actual minimum of 7.86, a 7% error, and a maximum of 16.0 versus the actual maximum of 18.8, a 15% error.

Metal Oxide Varistor (MOV) DMX Analysis File Released

Metal Oxide Varistor (MOV) DMX Worst Case Analysis File
MOV1 $12.50

(DMX files are available free to Design Master™ Professional Edition users who purchased or upgraded DM not more than one year prior to the DMX file release date.)

The MOV analysis determines whether a Metal Oxide Varistor transient voltage suppressor will (a) survive a specified surge voltage or current, (b) clamp the surge below a specified voltage limit, (c) not clamp the normal operating voltage, and (d) survive a specified number of surges. MOVS are typically rated with 8x20us current waveforms, and (just to be confusing) 10x1000us energy waveforms. MOVs also have a lifetime (number of allowable surges) that depends on peak current, pulse width, and temperature. To complicate things further, MOV clamping voltages are a nonlinear function of surge current. To help make the design engineer’s job a little easier, this analysis contains adjustment formulas for all of these factors. Also provides standard surge waveform requirements and helpful hints.

DMeXpert™ (DMX) files guide the user with pop-up instructions, component selection lists, standard part values, important formulas, and a variety of other tips that are activated when entering a Formula cell. It’s like having a design/analysis expert at your side.