Category Archives: Circuit Analysis

Transient Voltage Suppressor (TVS) DMX Analysis File Released

Transient Voltage Suppressor (TVS) with Optional Steering Diode DMX Worst Case Analysis File
TVS1 $12.50
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(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 Transient Voltage Suppressor analysis determines whether a TVS avalanche diode and optional steering diode will (a) survive a specified surge voltage or current, (b) clamp the surge below a specified voltage limit, and (c) not clamp the normal operating voltage. Good for any TVS diode and steering diode; just fill in the blanks using data sheet values, and get an answer in a few seconds. TVS diodes are typically rated with 10x1000us current waveforms. Steering diodes are typically rated with line frequency half-sine current waveforms. When the applied surge has a different waveform, however, the TVS and steering diode ratings must be adjusted accordingly. In addition, the ratings must also be adjusted for pulse width and temperature. 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.

2nd 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: Miraculous Emergency Landing on Railroad Track! / DESIGN MASTER TIP: AC Rectifier Bulk Capacitor Ripple Current / HUMANITARIANISM: Capitalism + Volunteer Engineering Helps Haitians / UNINTENDED CONSEQUENCES: Nanny Engineering / SHAMEFUL BEHAVIOR: Shanghai Euchips Industrial Co. Used Fake UL Label

NEWS BITE: Miraculous Emergency Landing on Railroad Track!

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Ground-Effect Robot Could Be Key To Future High-Speed Trains” by Evan Ackerman, 10 May 2011 IEEE Spectrum

DESIGN MASTER TIP: AC Rectifier Bulk Capacitor Ripple Current1 


Pretty good estimates of capacitor ripple amps for full wave rectifiers driven by low source impedance can be obtained by using the equations below. Note that an exact solution requires iteration, which can be done automatically by the Design MasterTM worst case analysis software. If you don’t have Design Master, you can get some quick results by first estimating the ripple voltage and solving for tC. Then calculate Vripple to see if your estimate was close. After a couple of iterations you will zero in on good values for tC and Vripple, and then you can solve for total capacitor ripple amps.

A PRETTY GOOD ESTIMATE for BULK CAPACITOR RIPPLE AMPS

1. tC = charge time, sec = ACOS(1-rRIP)/(2*Pi*f)
where
ACOS = inverse cosine function (COS-1)
rRIP = ripple ratio, Vripple/Vdc.
Vripple = ripple volts peak-peak = Idc*tD/C
Vdc = average DC output volts
Idc = average DC output amps
tD = discharge time = 0.5/f – tC, seconds
C = bulk capacitance, F
f = line frequency, Hz
2. Dc = charge duty cycle = 2*f*tC
3. Dd = discharge duty cycle = 1 – Dc
4. ICchg = ripple amps rms due to charge from full wave rectifier
= Idc*SQR(1/Dc-1)
5. ICdis = ripple amps rms due to discharge to load
= Idc*SQR(1/Dd-1)
6. ICload = rms content of pulsed load amps (e.g. input of switchmode regulator) if applicable. If load amps is purely DC, set ICload to 0.
7. ICtot = total capacitor ripple amps rms = SQR(ICchg^2+ICdis^2+ICload^2)

The great thing about analysis, as compared to simulators such as SPICE, is that you can learn a lot by reviewing analysis equations. For example, if you set the ripple voltage ratio to a desired amount (e.g. 15%), and rearrange the Vripple equation to solve for C, you can readily obtain a graph of the required ripple amps rating versus output current, regardless of input or output voltage. Now you’ve generated a general-purpose design guideline to use for numerous applications.

See the example graph below for the capacitor ripple amps requirement versus DC load currents from 100ma to 5 amps, for a 15% ripple voltage and a 60Hz source. For example, for 2 amps of load current, the capacitor will require a ripple current rating of 4.4A

1. Excerpted and revised from DACI Application Note, ” Why Power Designers Need More than SPICE to Avoid Blow-Ups.”

HUMANITARIANISM: Capitalism + Volunteer Engineering Helps Haitians

Non-governmental organizations operating on free-market principles can offer the most effective assistance to those in need. For an example click here.

UNINTENDED CONSEQUENCES: Nanny Engineering

Yes, the government does provide some essential functions. Unfortunately, it doesn’t have the self-control to restrict itself to those functions. The result is that we are plagued by governmental busybodies who like to justify their salaries by telling the rest of us how to behave, in areas that are none of their concern.

For example, as pointed out in Engineering Thinking, there have been numerous regulations passed that restrict our right to choose the products we may want, such as incandescent light bulbs. In that case, the government has deemed such bulbs unacceptable due to low efficiency. But if incandescent light bulbs are inefficient, that fact becomes evident in our electric bill; why do we need the government to tell us how best to spend our money?

Furthermore, perhaps some of us would, regardless of efficiency, prefer to use the incandescent type. But no, the governmental busybodies have decreed that you don’t get to freely choose. Forget about all of the other parameters that might be of more importance to you: short-term cost, color rendering, lifetime, reliability, and environmental hazards. Also, some folks in chilly climates might even appreciate the extra heat that incandescent bulbs provide. But none of these considerations matter to the one-solution-fits-everybody government.

Now, as typically happens following such governmental decrees, we find that they are rife with unintended consequences; e.g. the compact fluorescent lamps (CFLs) that the government wishes us to use instead of  incandescent bulbs have significant disadvantages:  (a) substantially lower lifetimes than expected, (b) may emit hazardous fumes (click here), (c) emit electromagnetic interference (EMI), (d) emit a color that can disrupt melatonin production and thereby cause sleep disorders, (e) sometimes create an irritating buzzing nose, (f) contain hazardous materials that pose significant environmental disposal hazards, and (g) will kill the domestic incandescent bulb industry, and replace it with products that are primarily foreign-made.

Some years ago the government illustrated similar brilliance by outlawing magnetic ballasts, again simply on an efficiency basis. It should be no surprise that the electronic replacement ballasts were more expensive, had shorter lifetimes, were less reliable, contained hazardous materials, and emitted a lot of EMI (so much so that some hospitals refused to use them because of their tendency to interfere with medical instruments).

Recently some smart engineers from China, unencumbered by the U.S. regulatory dictatorship, have created a magnetic ballast whose efficiency is better than electronic ballasts, at lower cost, longer life, higher reliability, using non hazardous materials. [1] Congratulations!

Sad to say, this is the sort of advance that was typically accomplished by U.S. engineers, back before the government decided to play Nanny Engineer.

Note 1: “A ‘Class-A2’ Ultra-Low-Loss Magnetic Ballast for T5 Fluorescent Lamps — A New Trend for Sustainable Lighting Technology,” Hui, Lin, Ng, and Yan, Feb 2011 IEEE Transactions On Power Electronics.

SHAMEFUL BEHAVIOR: Shanghai Euchips Industrial Co. Used Fake UL Label

Details here.

Announcing The Design Master Expert Assistant

DMXAnnouncing the Design Master Expert Assistant with the release of Design MasterTM V8

The DMeXpert™ (DMX) Edition guides 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.

DMX is ideal for the design engineer or project manager who needs quick and efficient “fill in the blanks” design validation in minutes rather than weeks. Based on DACI’s thorough and practical worst case analysis plus (WCA+) methodology, DMX uses expertly designed templates to facilitate analysis of a variety of standard circuits.

In addiDM8tion to its standalone function, DMX is an integral part of the just-released Version 8 of Design Master’s Professional Edition. DMX facilitates efficient organization and selection of circuit and part files, and also provides easy access to an organized array of tutorials and DMeXpert tips.

Circuit templates, part files, and help files can be accessed and edited by using the Professional Edition. This allows an organization’s design experts to use the Professional Edition to create DMX templates tailored to the needs of the company.

For more information, please click here.