Tuesday, November 26, 2013

Three Surprising Things about VMI's 5kV Diodes

 

 Did you know that....


1)  VMI offers over 45 different 5kV diodes? 


Neither did I!  I got to thinking about it because our 5kV diodes are popular devices.  The question came up because a customer called and wanted a recommendation.  I knew we offered quite a few, but I was surprised to learn there are more than 45 of them.  I know because I counted them.

45+ different 5kV diodes sounds intimidating.  Fortunately there are a couple of pretty quick questions that can help narrow down the search.

Three main diode characteristics include Vrwm, Io, and Trr (reverse voltage, forward current, and reverse recovery time, respectively).  There are more, but these define the device.  Different applications have different requirements.  As is true with many things in life, the answer to, "What's the best 5kV diode you make?", is, "It depends".

Higher operating frequencies require faster Trr (lower Trr).

Sometimes high operating temperature means you want to add a lot of derating, so even though the application might only use 2kV, if the temperature is high or there are a lot of voltage spikes, using a diode with a higher Vrwm rating can be helpful.

  • Current ratings of 5kV diodes range from 40mA up to 2.2A.
  • Trr ranges from 30ns to 3000ns.

And then there are the 5kV diodes that have reverse power capabilities, like the ZR50SG.  It's a 5kV, standard recovery diode that can handle up to 10mJ of reverse power.  The reverse power capability means under arcing conditions or voltage spikes of less than 10mJ, the diode will recover.

High reliability tested and QPL diodes are available too.  The options include axial-leaded glass body diodes tested to different levels of processing.  Military grade diodes use the JANTX, or JANTXV prefix such as JANTXV1N6525.

2)  Termination and Package Styles Abound?


The second surprising thing about VMI's 5kV diodes is the variety of termination and package styles.

Termination styles include surface mount, through-hole, and formed-lead.

Package styles include glass, epoxy, and molded bodies.

There are various combinations too, like a surface mount, molded diode (SMF6533 for example), and a formed-lead glass body diode, like the 1N6517LL.

3)  VMI's Diodes are "Multi-junction"?

There are many surprising things about high voltage diodes, not the least of which is that any diode over approximately 1kV is going to have more than one junction.  Essentially a 5kV has multiple die 'stacked' together in series.  The die come from the same wafer so differences are minimized.  Stacking silicon die is about the only way to achieve high voltage blocking capabilities. 

Get Your List of 5kV Diodes 


It's easy to get your list of VMI's 5kV diodes.  Next time you visit VMI's website, click on the "Diode Search" button in the upper right corner.  When the search page appears, select 5kV in the Vrwm (V) pull-down menu, and press the 'Search' button.

The results page includes a summary of all the 5kV diodes in pdf format, and links to their data sheets.  You can save the results page to your desktop, or print it out.

And if you're not sure what you need, give us a call.  We'll help you make the right selection for your application.
 

Friday, November 22, 2013

High Voltage Turkeys and Holiday Catalogs

Maybe the same thing happens to you.  Since the beginning of November, my mail-box has runneth-over with mail-order catalogs!  Every day two, three, four, or more catalogs are delivered.  

Holiday Catalogs

There are basically two categories of catalog mailings.  Some are from companies I have actually placed orders with before, in which case case they seem to amp up the rate of their delivery.  Sometimes it's as frequent as one every two or three days.  The second category is that of companies I have never ordered from, but are similar to companies I have ordered stuff from.

One year I collected all the covers of all the catalogs I received between November 1st and November 30th just to see how many I'd get.  I put up a big sheet of 36" wide butcher paper and pasted all the catalog covers on it.  When I filled that strip up, I added a second one, and then a third.  By the time my "art piece", entitled "Chri$tma$, was completed, it required three strips of floor-to-ceiling butcher paper and covered an area of 108 sq. feet.  I keep that in mind when the catalogs start showing up in the mail.

It's a major mystery to me how they got my mailing address!  Okay, not really, but I AM surprised at how SOON they got it.  I have not been at my current address very long, and when I moved I made a 'clean break' of it, meaning I discontinued some subscriptions and culled the mail-order catalogs (this was during my return-to-brick-and-mortar purchasing habits phases when it seemed local stores were threatened by the rapid rise in Internet purchases).

Oranges?  

Of course since then things have mellowed out again, but there is something to be said about buying local. For instance, the other day I noticed the oranges I'd purchased were from Australia.  I have nothing against Australia whatsoever, except that I happen to live in the biggest citrus belt in the WORLD!!! "Why", I asked myself, "am I buying oranges from half-way around the world, when it's orange-season right now?!"  The answer is, "Because that is what was available in the grocery store that I happened to be shopping in, and I needed oranges".  Sheesh!

High Voltage Turkeys and High Voltage Diodes

In the U.S., Thanksgiving is less than a week away.  Next Tuesday afternoon VMI will be distributing holiday turkeys to each and every employee just like they have for at least the last 23 years I've been here.  It's their way of making the holidays happier for everyone, including temporary and part-time employees.

And it is greatly appreciated!  Turkey, high voltage turkey, is part of Voltage Multipliers, Inc.'s holiday tradition.

I don't know what exactly high voltage diodes have to do with turkey, except that happy employees make for quality products, and quality products make for happy customers, and happy customers make for happy employees.  

Here's hoping your Thanksgiving holiday is a happy one!  

Monday, November 18, 2013

2kV and 3kV High Voltage, Higher Current Diodes


You may recall the post from November 6, 2013 on the differences between the 5kV, 70ns, 1N6517 axial-leaded and the equivalent 1N6517LL formed lead diode.

Not every application needs a 5kV diode.  Why buy a 5kV diode when a 2kV or 3kV diode will work, especially if it costs more?  Enter the 2kV 1N6513LL and 3kV 1N6515LL diodes.   


Cost Drivers and Advantages


Generally speaking, the higher the reverse voltage rating, the higher the unit cost.  Likewise, as the current rating (Io) goes up, or the reverse recovery time (Trr) goes down, the unit cost goes up.  There are other factors involved, but that generally holds true. 

The same advantages of decreased thermal impedance, higher forward current ratings, and pre-formed leads, holds true for the 1N6513LL and 1N6515LL diodes.  


2kV, 3kV, and 5kV high voltage diodes
High Voltage Formed Lead Diode
Axial-leaded high voltage diode style
High Voltage Axial-leaded Diode

 

Differences in Current Ratings and Thermal Impedance


Formed lead diodes have a higher current rating than the axial-leaded equivalent.  The larger diameter 99.99% silver leads are excellent thermal conductors.  The larger lead mass serves as a built-in heat sink. 

 

Diode Ratings and Comparisons
  

The 1N6513 is a 2kV, 70ns diode, as is the 1N6515LL formed lead diode.  Below is a comparison of the rated current and thermal impedance of the two devices.     

Axial-leaded 1N6513 - 2kV 70ns 

             
Current Rating:  2A @ 55°C
Thermal Impedance
      Lead Length
           @ 0.0":  3°C/W
           @ 0.125”:  6°C/W
           @ 0.250”:  12°C/W


Formed Lead 1N6513LL - 2kV 70ns 


Current Rating:  3.5A @ 55°C
Thermal Impedance: 
      Lead Length
             @ 0.0":  5°C/W
             @ 0.125”:  5°C/W
             @ 0.250”:  5°C/W


The 1N6515 is a 3kV, 70ns diode, as is the 1N6515LL formed lead diode.  Below is a comparison of the rated current and thermal impedance of the two devices.     

Axial-leaded 1N6515 - 3kV 70ns 

          
Current Rating:  1.5A @ 55°C
Thermal Impedance
      Lead Length
           @ 0.0":  3°C/W
           @ 0.125”:  6°C/W
           @ 0.250”:  12°C/W


Formed Lead 1N6515LL - 3kV 70ns 


Current Rating:  2.5A @ 55°C
Thermal Impedance: 
      Lead Length
             @ 0.0":  5°C/W
             @ 0.125”:  5°C/W
             @ 0.250”:  5°C/W

 

Quick Summary 

The same device in a formed lead format will have a higher forward current rating and lower thermal resistance over the axial-leaded device.  The 1N6515LL will have higher current ratings than the 1N6515.

Between devices, the 1N6515 family has higher Vrwm ratings and lower forward current ratings (Io) compared to the 1N6513 family.  this is true for the formed lead diodes too.  The 1N6515LL has a higher Vrwm and lower Io rating than the 1N6513LL.  Sound confusing?  Don't worry - here's a link to the data sheet.


Cost

An added feature of the 1N6513 family is one of the lowest forward voltage drops of any diodes VMI makes.  This is also a cost driver.  Unless you need a 70ns, high current, low Vf device, go with the 1N6515 family device if your application is cost sensitive.

The formed lead devices are typically less costly than the copper tabbed devices (i.e. 1N6515U, or JANTX1N6515US).


More Choices

Other choices are available.  Chose from different reverse recovery times, package styles, and current or voltage ratings.  VMI has one of the most comprehensive lines of high voltage diodes.  You won't want to miss out!


Wednesday, November 13, 2013

VMI’s Power Supply Design Team – Meet the Engineers


VMI’s high-voltage-power-supply design team is stellar.  The three main design engineers are Randy Bethel, Derek Onstott, and Alex Jiang.  Between them, they have over 40 years of design experience.  Bonus – they’ll be at the VMI Sales Seminar in 2014, so plan to come!



HeNe Laser High Voltage Power Supply
High Voltage Power Supply 
VMI excels at solving tough, high voltage problems.  Our most successful ‘success stories”, defined in terms of customer delight and continued production, almost always originates with a custom seeking help for a difficult design problem no other company is willing to tackle.  The reasons are obvious – other companies just didn’t have the staying power or resources to make it through the necessary multiple iterations that custom solutions often require.  Experience has taught us that dedication, focusing on providing the customer with what they want and need, and the patience to deal with moving targets, are all necessary ingredients to a successful outcome.  Design specifications change, or are unknown in the beginning, or even untestable.  It’s not uncommon to design tests and test procedures right alongside the actual high voltage power supply.

A lot goes into the design of a high voltage power supply, much of it ‘behind the scenes’.  In the beginning, the design engineers are highly visible and play a central role.  Nevertheless, they cannot and should not do it all.  They have the unflagging support of the Purchasing, Sales, and Production departments, plus testing technicians, manufacturing engineers, drafters, the machine shops, and plastic shops.

Electrical specifications are usually specific to the customer and their application.  They range in output voltage, output current and average power.  Specialized voltage and current outputs are also possible.    

In addition to electrical specifications, other customizable features include -

·         Custom housings – metal and non-metal

·         Customized encapsulation

·         Single, dual, multiple voltage and current outputs

·         Signal monitoring and control circuits

·         Feedback networks

·         Test points

·         Custom testing hardware & software

·         Specialized testing fixtures for burn-in and temperature cycling

Our expertise includes power supplies up to 125kV and 250W. 

Our designs are found in mass spectrometers, portable & hand-held x-ray applications, commercial paint sprayers, medical defibrillators, CRT displays, powering sensors & detectors, and other industrial and commercial applications.

If you have a tough, high voltage application, give us a call.  We’ll talk.  Moreover, there’s no obligation on your part.

 VMI is ISO9001:2008 certified.  We’ve earned DSCC’s award of Lab Suitability, and we’re an IPC member.

Wednesday, November 6, 2013

High Voltage Diodes - Formed Lead vs. Axial-leaded Terminations



So.  What’s the difference between a formed lead diode and an axial-leaded one?  Well, the most obvious differences are in the leads themselves.  

Axial Lead and Formed Lead

An axial lead is typically smaller in diameter and longer in length.  The leads are straight and ready to be trimmed and formed into a variety of shapes and lengths.  The axial-leaded devices are designed for through-hole connections.  
 

In contrast, a formed lead device is shipped with the leads already bent and trimmed in a surface mount configuration.   
 

Differences in Current Ratings and Thermal Impedance

Each has it’s strong point when it comes to electrical specifications.  The formed lead diodes have a higher current rating, largely due to a lower thermal impedance.   The formed leads are larger in diameter than the axial-leads.  In addition, the leads are 99.99% silver and excellent thermal conductors so the bigger lead serves as a kind of built-in heat sink.
 
For example, the axial-leaded 1N6517 is a 5kV, 70ns diode, as is the formed lead 1N6517LL.  Below is a comparison of the rated current and thermal impedance.



Axial-leaded High Voltage Diode - 1N6517
1N6517 5kV 70ns Axial-leaded   
1N6517 (Axial-lead) 
             
Current Rating:  1A @ 55°C
Thermal Impedance 
      Lead Length
           @ 0.0":  3°C/W
           @ 0.125”:  6°C/W
           @ 0.250”:  12°C/W




Formed Lead High Voltage Diode - 1N6517LL 5kV 70ns
1N6517LL 5kV 70ns Formed Lead

1N6517LL (Formed Lead)


Current Rating:  1.5A @ 55°C
Thermal Impedance: 

      Lead Length
             @ 0.0":  5°C/W
             @ 0.125”:  5°C/W

             @ 0.250”:  5°C/W

 

 

 

 

Pad Layout


The pad layout is different for each device.  They are not drop-in replacements, but they’re close.  Depending on your board layout, the changes could be minor, or a little more than minor.  

Cost

In terms of cost, the formed lead diodes are in the middle of axial-leaded devices and tabbed surface mount devices (1N6517U, for example).  They are considerably less expensive than the tabbed QPL devices such as the JANTXV1N6517US. 

The formed lead diodes (1N6517LL, for example), are a cost effective  alternative to the commerical and military versions of the tabbed devices when low thermal impedance and higher current ratings are needed.