Thursday, December 22, 2016

Running Diodes in Oil - New App Note

Voltage Multipliers Inc. LogoRecently concluded testing indicates that running high voltage diodes in oil may allow for operating beyond the forward current ratings (Io).

All cautions apply - we do not recommend exceeding the current rating of any diode without extensive testing in your application, and basically the trick is to keep the diode junctions cool.  In other words, strive to get the heat out.

Here's the App Note -  AN0400 - 1N6519 Power Dissipation in Oil

Give us a call if you have any questions - 559.651.1402, or visit the website for more app notes and FAQs.

1N6519 10kV 500mA 70ns high voltage diode
1N6519 - 10kV, 500mA, 70ns High Voltage Diode

Wednesday, December 21, 2016

How to Test Vf and Polarity in High Voltage Diodes

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High Voltage Diode Vf Testing

Here at VMI, by virtue of working in the niche high voltage area, we get all manner of customer questions about issues that are somewhat more complicated by virtue of our unique devices.  

Recently, a customer asked how they could confirm - 

              1)      The working ability of a high voltage diode 
              2)      Double-check the polarity of the device.


High voltage diodes have a higher VF than the ‘ideal’ model of 0.7V, so that many of the traditional ways of checking to make sure a diode is not failed shorted, or to verify the polarity of the device, will not work with high voltage diodes.  

Using a Fluke handheld multi-meter that has a diode check function, for instance, probably won’t be able to overcome the forward voltage of a diode, even at low currents.  A multi-meter is providing perhaps 2.4V and some of our diodes have a rated VF of over 30V!

VMI Vf and Polarity Test Methods

VMI measures the VF of our diodes using precision, current controlled power supplies capable of providing 50V or more.  Though not necessarily readily available to all users, the easiest way to test the polarity and functionality of a high voltage diode is a similar method.

Current Limiting

Current limiting a power supply to a low level of perhaps 100µA – 1mA and connecting it up to the diode will do the trick without much effort.  You need a power supply that can provide more voltage than the rating of the diode, but make sure the power supply is limited so that it cannot provide more voltage than the breakdown level of the diode. 

See the simplified block diagram below for an idea on how to connect the power supply up to the diode.  Depending on your power supply, you might need to use a current limiting resistor and an external current meter.

How To Tell the High Voltage Diode is Good

Once you have your setup, the diode should conduct your current (100µA – 1mA, depending on how you limited the supply) in the anode-cathode direction.  Reversing the current flow by flipping the diode to cathode-anode should block the current down to the leakage levels of the diode (less than 1µA).  If the diode conducts in both directions, then you have a failed (shorted) diode.  If current does not flow in either direction, you have a failed (open) diode.

Questions?  We would be happy to help, so give us a call - 559.651.1402.

Wednesday, June 15, 2016

Tom Rowan Jr., Former NASA Engineer, Has Retired

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Congratulations to Tom Rowan, former NASA Engineer, and VMI Sales Representative for many years.

Tom was recently honored by NASA.  His name will be inscribed on the "Wall of Honor" at the NASM monument in Washington D.C.

In Tom's own words, "In January of this year, I turned 75 years old, so I decided to finally retire, after 55 years of working as an engineer and marketing consultant to this Aerospace and Energy Components industry.

A week ago, I received an "Award" from the National Air and Space Museum. That certificate announced that my name would be added to the monument walls at this DC museum, in about a month or so. This documentation is in recognition of all the amazing motion control devices I invented for the aerospace controls and motion devices which were used on NASA space vehicles between 1960 -  1973.

I really appreciate this special recognition, and want to share this announcement with some of my friends and family."

Tom Rowan Jr. - NASA Mars - Viking Soil Sampler

Tom Rowan Jr., Apollo 11 Moon Landing

Wall of Honor - Tom Rowan Jr.

Congratulations to Tom Rowan, Jr. upon retiring.  Best wishes in the years to come.