Voltage Multipliers Inc.

Photonics West Show - Going on now

2012-01-26T13:30:00.000-08:00

Daniel and Margaret are there, along with Jeff Day, President of CalRamic. Here are a few photos....The exhibit is at the Moscone Center in San Francisco. Stop by for a visit - Booth 5323

Writing Failure Analysis Reports - Oh Joy!

2012-01-24T13:16:00.000-08:00

One of the more unpleasant aspects of engineering is having to occasionally perform a failure analysis on a returned part and then write a Failure Analysis Report (FAR) about it.

When a customer returns a part, it means it was non-compliant in some way. Maybe it didn’t meet the mechanical specifications, maybe it shorted out electrically, or maybe the cause for return was cosmetic in nature. Maybe even there was nothing wrong with the part – it met all the specs – but didn’t work properly in the customer’s application.

From an engineering point of view, a returned part means the customer is probably unhappy, or concerned about additional failures you may or may not be aware of. If it left your factory, then the part failed in your customer’s system, or their customer’s system, or somewhere ‘in the field’. Many times there is more than one part, maybe they’re stockpiled somewhere, or the customer has a large inventory on hand.

Often there is a lot of pressure to get it right in determining the cause of failure, and chances are, you might be feeling overwhelmed. Many times there is a lack of information about operating conditions in the field, how the part was being used, or even how it failed. Unknown conditions like voltage transients can be particularly tricky, as can any intermittent condition. Trying to figure all that out is part of writing a FAR.

Keeping in mind the humorous aspects of human nature, not all engineers approach the analysis in the same way. Some are determined to prove the design is good, and the customer just misused or broke the device. Others assume the design or manufacture was inherently flawed. Most of the time, the truth is somewhere in the middle, and in the end, has to be substantiated by ‘the facts’.

Either way, the goal is to keep the customer happy. Sometimes that means writing Failure Analysis Reports and making sure the parts never break again. Painful as they may be, once in a while, good things come out of FARs. Sometimes they spur a new revision on an old design, or a new design, and sometimes a re-examination of the manufacturing process or raw materials. And that can be a good thing!

What was your worst ever Failure Analysis experience?

Going to the Photonics West Show Next Week?

2012-01-20T16:38:00.000-08:00

If you're in San Francisco next week at the Photonics West show, stop by Booth 5323 and chat with Daniel or Margaret. The show goes from Jan 24th through Jan 26th.

Look for us!

Increase the Recovery Softness of Fast High-Voltage Diodes

2012-01-16T15:59:00.000-08:00

The January issue of Bodo's Power Systems (pg. 30-pg. 37) features an article on how to increase the recovery softness of fast high voltage silicon diodes - diodes up to 1kVrwm. Very good technical discussing that takes into consideration factors such as wafer thickness, carrier life time, and such.

Are Pb-free Processes and Products Worth the Effort?

2011-12-29T09:45:00.000-08:00

Here is a link to an interesting discussion on whether the move towards Pb-free products and manufacturing processes were worth it.

The article is from ECN magazine and discusses the opinion of whether replacing Sn/Pb solder with Pb-free solder was worth the effort in terms of measurable environment benefits.

Decide for yourself.

High Temperatures and Semi-conductors

2011-09-23T15:10:00.000-07:00

Great article on high temperature semi-conductor solutions for down-hole applications....

This article discusses the various temperature extremes needed for down-hole applications, and addresses which type of semi-conductors work best for certain conditions.

Sales Seminar - April 2012

2011-09-19T09:05:00.000-07:00

Update - The Sales Seminar has been postponed. We hope to have a firm date by 2012 3Q. We apologize for any problems this may have caused you.

Only Seven (7) months until the 2012 Sales Seminar! It will be five (5) years since we were altogether in 2007 and all of us at VMI and CalRamic are looking forward to seeing everyone and a informative exciting time in April.

Location Information

Who: All VMI USA and International Representatives

When: April 12th arrival- April 15th Departures 2012

Where: Visalia Marriott Hotel
Phone: (559) 636-1111 Fax: (559) 636- 2285

Dress: Business casual / Friday evening dinner Business attire

Preliminary Agenda

Arrivals: Thursday April 12, 2012 and Evening Welcome Reception

Friday April 13, 2012
Breakfast
VMI Plant Tour
Sales Meeting
Evening Dinner

Saturday April 14, 2012

Breakfast
Sales Meeting
Luncheon
Saturday afternoon- Activity
Saturday Evening Dinner

Sunday April 15, 2012 Departures

What we need from All of you

We need your confirmed reservations NO later than March 1, 2012.

To make the Sales Seminar successful VMI and CalRamic need to know what All of you would like information on at the Seminar. Please provide your suggestions on topics to discuss by December 1, 2011 or sooner.

If you have any technical issues you want addressed specifically please let our engineer Daniel Deschenes (ddeschenes@voltagemultipliers.com) know so he can organize and present the information you want and care about.

VMI and Calramic engineers will be happy to help you with individual questions, but any information or topic you think would help others is appreciated. Our engineers want to help you sell our products with accurate technical information and rapid and precise information. Help us help you!

More information will be provided as we move closer to April 2012.

Thank you!

Why Multipliers Do Not Perform Optimally at 50-60Hz

2011-09-07T12:14:00.000-07:00

Every once in a while we get a customer inquiry about running voltage multipliers at frequencies of 50-60Hz, which we try to graciously decline, since most of our multipliers are designed to run at 10kHz or higher.

The problem with low frequency multipliers (50Hz – 60Hz) is the slow oscillation at lower frequencies does not charge up the capacitors in the multiplier quickly enough to keep up with normal discharging during the negative cycle.

The reason the voltage multiplier works the way it does is because the capacitors are able to store energy to supply other circuitry down circuit.

Voltage multipliers work best at 10kHz and higher.

Sometimes a D.C. input is used, but in order to generate a high D.C. output voltage, the D.C. input has to be converted to an A.C. signal. This can be done by using a fly-back oscillator or PWM controlling the frequency, and stepping up the signal via a transformer, before being fed into the multiplier.

We normally consider a configuration of this type to be more in line with a power supply, since it incorporates signal conditioning, and a high voltage multiplier.

Build Your Own SiC LED

2011-05-11T07:43:00.000-07:00

Is this cool, or what? The author, Michael T. Lippert, takes raw materials, and creates a SiC LED. No, it's not really for use on a pcb or as part of a circuit, but it IS great 'scientific' fun.

Check it out....

DIY SiC LED

2012 Sales Seminar

2011-05-03T09:35:00.000-07:00

VMI will be hosting a Sales Seminar in April, 2012. Included will be Sales, Marketing, and Technical presentations, plus an in-depth plant tour.

We look forward to greeting old friends, and making new ones!

More details to follow....

Quantum Dots - Doped and Ready

2011-04-07T11:29:00.000-07:00

Scientists in Israel have figured out a way to dope Quantum Dots to form a p-type and n-type pair - the basic building block in creating semiconductor devices such as diodes and transistors.

They are particularly well-suited for solar panel applications, or ones needing to be inserted into flexible plastic materials (flex circuits for instance).

An exciting development....

Mercury Fly-by Images

2011-04-05T14:01:00.000-07:00

It's no accident that the Mercury fly-by space probe was named "Messenger". You probably recognize the winged Roman god, Mercury. He was the messenger of the Gods.

Anyway, NASA recently released the first images of the planet Mercury taken by the Messenger probe, with more to follow.

Launched in 2004, it took almost 7 years to get there.

I dunno....if you're like me, photos of other planets, our solar system, and the universe STILL makes me jump for joy!

Summary of Status of Nuclear Power Plants Worldwide - The Impact of Fukushima

2011-03-25T15:04:00.000-07:00

A blog post by Prach Patel in IEEE Spectrum, updated 3/24/2011, provides a comprehensive list of worldwide nuclear power projects and their status after Fukushima.

Some countries have issued a moratorium, others have made it clear they plan to proceed, albeit only after additioanl saftey tests, and analysis.

Find out which ones....

Alcholic Beverages Aid in Superconductivity? Really?

2011-03-24T11:51:00.000-07:00

While it would be easy to draw interesting, and possibly amusing, social parallels of alcohol and conduct(ivity), this study doesn't do that. Instead, it focuses on properties needed to produce superconductivity, and how some alcoholic beverages seem to facilitate that characteristic in certain materials.

Really.

Study Reveals Alcoholic Beverages Induce Superconductivity

Article by Paul Whytock, appearing on-line in Electronic Design magazine.

VMI is at the 2011 Pittcon Show in Atlanta

2011-03-16T11:59:00.000-07:00

Drop by the booth to visit with Daniel Deschene and Karen Spano. They're at the Pittcon show going on right now in Atlanta, GA.

The show goes through March 17th. We're in booth #4642.

Now's the time to catch them if you need quotes, or new designs for high voltage componets or power supplies.

The venue is the Georgia World Congress Center.

See you there!

Breakdown in High Voltage Lead Insulation - Failure Mechanism Found by Researchers

2011-03-04T13:10:00.000-08:00

If you've done high voltage design for any length of time, you've probably encountered problems with punch-through on high voltage insulated lead wires. (If not, you have something to look forward to).

Researchers now have an idea about how failures occur in the insulation, and it has to do with applied voltage. No surprise there, but what is surprising is how the damage actually occurs. First comes creasing, then comes cratering.

It's exciting to think that info from this study may lead to improvements in lead wire insulation. Learn more about the research conducted at Duke University.

Lightning Made by Humans - Images Captured by a Camera

2011-01-31T15:40:00.000-08:00

Very interesting read about lightning, and x-ray radiation. The pictures show that most of the x-ray radiation is carried in the tip of the lightening bolt.

Talk about very, very, VERY, high voltage....and the speed of the camera needed to capture an image of lightning.

Lightening Captured by Incredibly Fast Camera

Photonics West Show in San Francisco - Starts Tomorrow!

2011-01-24T11:35:00.000-08:00

Hi y'all,
VMI is attending the Photonics West trade show in San Francisco at the Moscone Center. Stop by for a visit, our booth number is 4325.

If you can't make it tomorrow, 1/25, don't worry - the show goes through 1/26. It's a great opportunity to talk with like-minded engineers, designers, and scientists.

Ask for Karen Spano or Daniel Deschenes.

See you there!

VMI Celebrates 30th Anniversary

2010-11-01T11:10:00.000-07:00

VMI was founded on November 10, 1980. To celebrate this date, VMI will host a 30th Anniversary Luncheon for all employees on Friday, November 12th, 2010 at 1:00 p.m.

Thank you for your hard work and dedication over the years.

We look forward to the next 30 years!

What We Think is Unique About Us….What Do YOU Think?

2010-09-23T13:28:00.000-07:00

VMI has been around for thirty years. We’ve outlasted many of our competitors, who’ve been bought and sold countless times. So what makes us different, (and so darn lucky!)?
Here’s what I think –

First, VMI is privately held. That gives us a huge advantage. We’re not traded on the Stock Market, and that means we can focus on long-term goals. Taking the long view sometimes means sacrificing a percentage of profitability in the short run. That can affect quarterly profits, and if quarterly profits are not maximized, Wall Street throws a fit. So, basically, because VMI is a private corporation, we are not as susceptible to the same corporate whims as, say, other high voltage manufacturers.

Secondly, VMI has great customer service. Regardless, VMI strives to be fair in all transactions, including tooling, NREs, and returned material. Related to customer service is our Product Guarantee Policy. If it doesn’t work, return it. There are, of course, some exceptions, but when there is any doubt, we would rather err on the side of customer service.

Third, VMI’s strength is our ability to work with customers to solve complex problems. No other company will go the distance to make sure the product meets the customer’s need – especially if the design cycle is a long one.

Fourth – we are constantly striving to improve our products and services. We listen to our customers, to their suggestions, comments, and complaints. And we try to do something about them. Always, we try to make it better.

So basically, we think we’re pretty unique because we really are customer focused. Without our customers, we wouldn’t be here.

What do you think is unique about VMI?

Who is Liable When Customer Supplied Materials Fail?

2010-09-17T16:05:00.000-07:00

One of VMI’s strong points is our ability to work with the customer on custom designs.

Every once in a while there is a need for ‘customer supplied materials’. The reasons are varied, but usually have to do with material availability, timing, ease of shipping, or economies of scale.

Sometimes material will be shipped to a customer’s facility where they make a modification to it. That same material is then shipped to VMI to be used in the manufacture of products for the same company supplying the material. At that point, we've come full circle. The customer is the supplier, is the customer......

Questions of product liability can get complicated quickly.

One of the big questions is, “What happens when you build a part with customer supplied material, and that part ends up being scrapped?” Related questions include, “How do you handle the loss in material and labor?”, “What if we damaged the material they supplied, and caused the part to fail?”, or, heaven forbid, “What if they supplied us with defective material, and we built parts with it?” Those are just a few questions, off the top of my head!

Determining liability for a failed assembly can be difficult. Just the process of performing a failure analysis requires resources that may or may not be split equitably. The problem may even be indeterminate. Then what!?

Dealing with situations like these requires a good, solid relationship between companies. Accurate and timely communication is a must.

How does your company handle situations like these where your customer is also your supplier?

Sometimes We Have to Say “No Bid” – Four Determining Factors

2010-09-14T14:45:00.000-07:00

VMI has been in business going on thirty years. Way back when, VMI made voltage multipliers. (In case you didn’t know, VMI is short for “Voltage Multipliers, Inc.”). When the world’s supply of high voltage diodes joined the endangered list in the 1980’s, VMI invested time and resources in manufacturing their own. The intent was to keep the supply going so they could continue to build assemblies.

Then, a funny thing happened on the way to the future. With the advent of LCD displays during the 1990s, demand for voltage multiplier assemblies took a nose dive. Fortunately for VMI, by that time, high voltage diodes had become the mainstay of business.

Today, VMI boasts several product lines, many of which came about as a result of VMI’s ability to find solutions to customer’s unique applications. Almost always, the applications were technologically challenging, fast paced, and definitely not mainstream.

Some projects are clearly not a good fit, and entering a ‘No Bid’ is a no-brainer.

But what about the borderline cases, the ones that don’t fit neatly between the lines? The ones that, maybe, with a little bit of tweaking and a lot of hard work, might clean up nicely…? Sometimes the calls are pretty tough.

Rarely do one or two factors flag a project as no-bid. Frequently it is the compound effect of several factors. In the end, a project has to be profitable in one way or another. The profit may be tangible or intangible, but it has to be there.

There are many factors that influence the decision to bid or no-bid. Here are four of them, in no particular order -

1. Resources - Based on the estimated complexity of the project, do we have the resources necessary to deliver a design within a reasonable amount of time? Are there minimum buys on materials? If so, how much? Minimum buys, and lead times, can make a project less attractive, and are often things VMI has no control over.

2. Need By date – If the need date does not allow a sufficient amount of time for design and verification, it’s a red flag. Power supply applications take significantly longer than typical rectifier or multiplier designs. The turn-around time on a simple rectifier or multiplier might be as short as 24 hours. In any case, there has to be sufficient time allowed for design, test, and possibly multiple iterations.

3. Life-time quantity – There are no hard and fast rules about life-time quantity, but a certain amount of potential - future business opportunities, developing a relationship with a new customer, or even supporting an existing customer on a financially negative project – has to be present.

4. Target Price - Is the target price reasonable? If we can’t meet the target price, how close can we come, and how soon can we get there? Often prices come down after the prototype stage. This can be attributed to design stability, taking advantage of scale – i.e. purchases made in volume, continuous process improvement, and NREs that may have been amortized into prototype pricing. If the target price is $5 for a 100kV power supply for a life-time quantity of ten, it is apparent up-front that a project like this is not a good fit. However, if the unit price is $500 for a monthly quantity of 10, it may warrant a closer look.

In the event VMI no-bids a project, we do it with great regret. It pains VMI to have to no-bid a project. We love a good challenge. Solving technical problems pushes the limit on our comfort zone and helps us grow.

In the event we “no-bid” a project, we will do everything possible to steer the customer in the right direction, even if it means sending them to one of our competitors.

As they say, "Timing is Everything"....

Challenges of Off-shore Outsourcing

2010-09-08T13:34:00.000-07:00

Outsourcing is a common corporate cost-cutting strategy. Many of us live in fear of losing our jobs to call-centers located in other parts of the world, or cheaper, imported products.

It's not going away any time soon.

When it comes to manufacturing, outsourcing key components can be especially troublesome. If, on the other hand, the component is established, supply is stable, and multiple sources are available, out-sourcing may not be much of an issue.

When problems crop up, as they invariably do, accessibility to the supplier is the key to finding a solution quickly and painlessly. There are many reputable companies worldwide, but, hey, let’s face it. Communicating with a company a few time zones away is difficult enough. As the number of time zones goes up, communication becomes almost impossible. I haven't seen any scientific data, but for every increase in time zones, I'll bet there is a corresponding increase in difficulty of communicating with the supplier. Anyone care to hazard a guess? Does it double? Triple? Quadruple?

Off-shore outsourcing gets complicated very quickly. Tariffs and trade restrictions change fast, and you practically need a legal department to stay on top of things. Cultural differences and language barriers add a whole new level of complexity.

The bottom line is, if delivery and consistency are important, keep it in-house.

If it is one of your core competencies, don’t even think about out-sourcing it.

Anything else is fair game.

More on Opto-couplers

2010-09-03T13:55:00.000-07:00

Opto-couplers are optically isolated devices. They come in handy when systems of different voltage levels have to be coupled together, and when controlling noisy inputs or outputs. They are often used to provide system isolation, or as a remote system control.

Specific applications include

high-end instrumentation
lab equipment
linear regulators
high voltage switches.

The idea is pretty straightforward – forward current through LEDs generate smaller leakage current in a photo-diode. The leakage current is linear, and can be monitored and controlled.

VMI manufactures several styles of opto-couplers in several breakdown voltages.

• The OC025 features the lowest breakdown voltage, and also, not coincidently, has the smallest foot print (approximately .46” x .46” x .33”, (11.7 x 11.7 x 8.3mm), excluding leads.

• The OC100 family has a Vrwm of 10kV to 15kV, depending on the selected product. Dimensions are approximately .45” x 1.0” x .32” (11.4 x 25.4 x 8.1mm), excluding leads.

• The OC250 has a Vrwm of 25kV, and comes in the largest package, measuring 1.4” x 2.1” x 1.0”

For more info on applications, visit our website.

Get the Heat Out!

2010-08-23T10:45:00.000-07:00

Rectifier Assembly Design Considerations - Thermal Management

When I think of rectifier designs, high voltage stacks, single phase bridges, and three phase bridges come to mind. These are all made using strings of high voltage, discrete diodes soldered together.

Thermal management is critical to long-life , and reliablity.

Here are several methods to help you 'get the heat out'...Continue >>

High Voltage Power Supply Product Review

2010-08-19T13:30:00.000-07:00

VMI makes a wide range of high voltage power supplies available in large and small packages. Below is a brief summary…

XRS Power Supply

Portable X-ray Power Supplies

Compact and lightweight, the XRS family is designed for portable X-ray applications.

Output voltages are -40kV and -50kV, and up to 10W of power.

CRT Power Supplies – CRS080G40 and CRS120G40

CRT Supply with Anode Connector

These are PCB mounted power supplies with anode style connectors.

Available in 8kV and 12kV, both power supplies operate on 15VDC

CRS110G50 and CRS180G60

CRS110 and CRS180

These are fully enclosed, have higher output voltages and currents, and feature wire terminations.

Applications include CRT displays, sensors, and delicate equipment..

Output voltages are 11kV and 18kV; the output current is 550uA max.

LP6 HeNe Laser Power Supply

HeNe Laser Power Supplies

The LP6 family was designed to power HeNe lasers.

It supplies a Start Voltage of 6W at 10kV, and works off of a 5V, 12V, 15V, or 24VDC input.

It is rugged, lightweight, and features high efficiency, and low ripple voltage and current.

HVP Industrial Power Supply

The HVP family features industrial size power supplies encased in NEMA 12 enclosures. Output voltages range from 50kV to 125kV.

HVP125 Power Supply

Power supplies are available in positive or negative output voltages, and can deliver up to 250W.

For more info on standard power supplies, visit VMI's High Voltage Power Supply site.

Custom designs available. Contact us.

New App Note - Make a High Voltage Op-Amp Using HV Opto-couplers

2010-08-16T15:10:00.000-07:00

D.Deschenes

Use two high voltage optocouplers in a push-pull configuration to make an op-amp featuring a high DC gain loop, and wide bandwidth.

App Note 0300 - High Voltage Op-Amp Application Note

GaN Ready for High Voltage?

2010-07-09T09:07:00.000-07:00

Are GaN power switching devices such as IGBTs, a potential, cost effective alternative to silicon?

GaN based transistors up to 600V have been demontrated by several companies to perform well in circuits. The future looks bright.

Decide for yourself....Where are the High-Voltage GaN Products?

VMI Websites

2010-06-30T11:36:00.000-07:00

Hey, I know you know VMI makes high voltage diodes, multipliers, opto-couplers, and such, but did you know we also manufacture power supplies?

We have two websites - one is devoted to diodes and diode assemblies. There is a lot of good content on high voltage diodes, data sheets, testing, design, to be found there. And it's not just about diodes.

Our second website is devoted entirely to high voltage power supplies. Here you'll find data sheets on our standard power supplies. They range from 8W to 250W, 8kV to 125kV.

Applications vary from medical & CRT types, to industrial strength commercial, and include portable X-ray supplies, and more. But don't take my word for it, check it out.

If you don't see something to fit your needs, contact us. We design custom power supplies too.

Voltage Multipliers and Social Media

2010-06-21T14:54:00.000-07:00

Social Media (SM) has been around for a while now.

Part of my job is to find ways to incorporate SM - Facebook, Twitter, You-Tube - into our general media plan.

I must say I find the concept very exciting, but not exactly easy. Most people think of SM as, well, social, rather than business.

B2B companies are lagging behind in the adoption of SM. Less than 50% of big corporations have a blog or Facebook account. I am proud to say VMI has both.

On the other hand, SM could be a great way to build a community based on high voltage design. Think of the possibilities! Customers could interact directly with engineers, or even other customers. We could discuss problems and solutions, possible alternatives, new technology, old technology.....How cool would that be?

Sales and Sales Reps could get in on the action too. With a blog and Facebook at their fingertips, no more checking emails or worrying about who was or wasn't copied on the latest correspondence.

As a blogger and SM newbie, please forgive my zealousness. Should you opt in to VMI's blog, we promise to protect your privacy. We won't sell your info and we won't bother you with multiple daily posts.

So do me a favor, please....Subscribe to VMI's blog now.

Respectfully yours,
kholland

High Voltage Design Issues

2010-05-24T14:21:00.000-07:00

A lot of times customers request 'ratings' on components used in assemblies. It can be a difficult question to answer because there are so many variables.

For instance, one manufacturer might specify a given capacitor as being able to withstand 5kV, with a thickness of 0.1 inches.  Another manufacturer may specify the same voltage, but a thickness of 0.12 inches.

At VMI, we tend to be conservative when it comes to voltage ratings on capacitors, but it depends on a lot of things - for instance, current draw, operating temperature, and frequency, just to name a few.

One solution is to specify the volts/mil stress and let the customer decide if they're comfortable with that.

I always liked the story about how Orville and Wilbur Wright used to do it - they'd switch out a nut or bolt until it broke, then beef it up a little. They used trial and error to specify minimum limits.

How do you deal with component ratings? Do you assume the manufacturer includes a margin of error? Are you comfortable with pushing the limits on maximum ratings?

-kholland

Ambient Light Is Everywhere! - The Effect of Ambient Light on High Voltage Opto-couplers - by D.Deschenes

2010-05-12T10:27:00.000-07:00

The fact is, all of VMI's glass-body multi-junction silicon diodes are affected by ambient light to some small degree.

A condensed explanation of the physics of the interaction is this: A photon from ambient light strikes an electron in the silicon of the diode and causes movement of the electron, creating a current with a direction depending on the applied electric field on the diode. For VMI’s typical diodes, the silicon is passivated with a hermetic glass, which is opaque and keeps ambient light from significantly affecting the diode.

"Problem" Ambient Light in Opto-couplers

Our opto-couplers use that same principle to create a relationship between low voltage infrared LEDs and an exposed silicon high voltage diode. To make the opto-coupler sensitive to the infrared light of the LEDs embedded in the device, the entire opto-coupler is molded in an optically clear plastic. Because the part is molded in clear plastic, the exposed silicon of the high voltage diode can be excited by ambient light. Though the affect of ambient light on the leakage of the high voltage diode is small, it can be of particular annoyance when you desire the opto-coupler to be ‘off.’

The Solution

Typically, leakage caused in an opto-coupler by ambient light is solved by encapsulating the entire circuit in which the opto-coupler is being used. This is done usually for the primary reason of keeping high voltage from arcing and causing damage in the circuit. Over-encapsulation of high voltage sections within an assembly is quite common. Another possible solution to limiting ambient light would simply be to place the opto-coupler in an opaque box. Although I would refrain from using a metal box unless you have encapsulated the high voltage areas of the circuit. Because, you know…. arcing. Just a thought.

Web 2.0 Expo

2010-04-30T13:47:00.000-07:00

Hey y'all,

I'm getting ready to leave for next week's Web 2.0 Expo in San Francisco.

I'm looking forward to learning more about Social Media, Social Networking, Search Engine Optimization, and Search Engine Marketing.

I'm excited to attend because I always come back with tons of ideas, and lots of inspiration.

So, I'll see you week after next!

On behalf of VMI,
'Till next time,
-kholland

Write Like Ernest Hemingway - Are You Up To The Challenge?

2010-04-20T15:51:00.000-07:00

Some people claim the best story Ernest Hemingway ever wrote was written in six words....

"For Sale: Baby shoes - never worn".

Those six words speak volumes!

Well, what started out as a challenge to a few engineers here at VMI netted a couple of gems of our own. And here they are -

"Silly humans: big brains, small thoughts". - DD

"California dreaming: free living. Bankruptcy". - RM

"California living: Clean environment, “No trespassing” - also by RM

Are you up to the challenge of writing a story in six words?

ASMS - American Society for Mass Spectroscopy Conference - Booth #117

2010-04-16T15:16:00.000-07:00

Visit VMI at the 58th American Society for Mass Spectroscopy Conference May 23-27, in Salt Lake City, UH.

It will be held at the Salt Palace Convention Center.

Over 3,500 scientists are expected to attend.

We'll see you there! - Booth #117.

More details on the convention

Trr in Multi-Junction High Voltage Diodes and Switching Circuits

2010-04-15T13:46:00.000-07:00

When selecting a high voltage diode for your application, one important characteristic to examine is Reverse Recovery Time, or Trr – especially in fast switching applications such as Switch Mode Power Supplies (SMPS).

When a diode is blocking, a reverse voltage exists between the anode and cathode terminals. Ideally, zero current flows. In this state, the cathode is more positive than the anode. The diode acts like an open circuit. In reality, there is a small current referred to as reverse current, Ir, usually in the nano-amp range.

When a diode is conducting, i.e. acting like a short circuit, current passes through the diode from anode to cathode. The anode is more positive than the cathode. This current is called Forward Current, Io. Io generates a relatively small Forward Voltage drop, Vf.

Sample Diode Data Sheet

Reverse Recovery Time, Trr, is the time it takes the diode to transition between blocking mode and conducting mode.

Trr is especially important in the case of multi-junction diodes used in fast switching applications such as Switched Mode Power Supplies. To create diodes capable of withstanding greater than 1,000V reverse voltage, die are stacked in series and then passivated, thus creating a high voltage diode.

For a SMPS, and other switching applications, running at 50kHz, the slowest Trr recommended for a diode is 70ns. Diode Trr is actually a measure of the reverse recovery time of the fastest die in the stack.

Under most circumstances, stacking die in order to achieve a higher blocking voltage, Vrwm, is not a problem. This technique is common. However, a potential area of concern is widely varying reverse recovery times within the discrete diode. For instance, a problem can arise when individual junction times vary by several orders of magnitude, and operating frequencies approach 50 kHz, typical in switching applications. In this situation, one would expect a diode to fail shortly after turn-on. Oft times, die Trr can be confirmed to range between nano-seconds and micro-seconds.

The solution to the problem of widely varying die Trr is to construct a diode using die cut from the same wafer lot. During the manufacturing process, VMI takes great care to do just that. Our standard manufacturing process greatly reduces concerns over potentially mismatched reverse recovery times.

Every application is different, and many factors can impact how well a component performs. Things to consider include operating conditions, operating frequency, wave-shape, and circuit topology. Trr requirements should be evaluated on a case-by-case basis.

With that said, it is generally not necessary to match die Trr in stacked diodes as long as the die come from the same wafer lot.

With VMI diodes, mismatched die Trr is nothing to worry about.