Thursday, August 14, 2014

An Unconventional Comparison Between High Voltage Diode Selection and Teaching

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 I have been a student on and off over the years, and am quite comfortable in that role.  Things like registering for classes, logging on to college servers, checking school email, posting to discussion boards, submitting homework on- line, taking timed finals dressed in p.j.s and fully armed with a fresh pot of coffee…Yes, I know the drill. 
Recently I started teaching a class at the local college. Now, for the first time, I am on the other side of Blackboard.  It has definitely been a learning experience – much like specifying diodes in a high voltage application – and one I’ve enjoyed immensely.  

For instance, navigating the ins and outs of submitting final rosters, requesting faculty office hours, dropping students who don't show up, and submitting paperwork to Human Resources, can be daunting for the first timer trying to learn my way around.   

Nevertheless, like any new challenge, perseverance furthers.  Just like the first time you have to specify a diode.  There are many diodes to choose from.  So, where to start?  A good place is the reverse voltage requirement.  Designers usually have a good idea of what is needed.  They may not know if it should be 3kV, 4kV, or 5kV, but even knowing that narrows down the field when you can choose from devices between 2.5kV and 45kV.    

Once the reverse voltage has been selected, work on the next important rating – usually either Forward Current, Io, or Reverse Recovery Time, Trr.  Not all current ratings and reverse recovery times are available in all reverse voltages.  If you select a particular reverse voltage that doesn't come in a specific current rating, you might have to start fresh by re-examining the voltage and current requirements.  A decision may be needed to determine which is more important - current or voltage. 
Sometimes a faster recovery time is more important than the current rating, or vice versa.  Sometimes the most important factor has less to do with electrical ratings and everything to do with the package or termination style.  Through-hole printed circuit boards may want to stick to axial-leaded devices, which can limit choices in voltage and current combinations.  The same is true for surface mount applications.  Not all SM diodes come in is every current and voltage rating.  

Even so, once you’ve been through the selection process, it’s a lot easier the second time.  Help is never further away than a phone call or email.  Contact VMI is you need help selecting the best diode for your application.

I hope you enjoy selecting a diode as much as I’ve enjoyed my first week as a college prof.  

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