[Elecraft] K2 Frequent Frier Club

[Don Wilhelm]

John,

I guess no-one except myself looked at the data sheets for the drivers.  
They clearly show the snubber diodes.  Do a Google search for 'ULN2803 
datasheet' and/or 'TD62083AP datasheet' if you need to see the diodes.

The snubber diodes are in the octal relay driver chip, and yes, they 
will work more than once unless the driver chip is fried.

If you look at the data generated by Jack Smith and posted just today, 
you will find that the inductive kick voltage will be snubbed at about 
14.4 volts, so the 50 volt capacitors should be fine.  Your prior ESD 
problems do present an uncommon set of events, and based on that fact, 
you may want to go with the 100 volt caps, but I do not believe they are 
necessary.

73,
Don W3FPR

Jferg977 at aol.com wrote:
> the "Kick" discussions responding to my question about why caps would  fail 
> in the low-band filter relay firing circuits on my K2/KPA100 have been very  
> interesting.  
>  
> That there could be such a kick was not a surprise to me so much as that it  
> could be so enthusiastic.  Don Wilhelm reports that the "relay driver" in  the 
> kpa100 has such diodes.  Where? inside the relay enclosure?  It  doesn't seem 
> like shunting off this higher voltage  in the octal  driver would work more 
> than once.
>  
> Suppose the diode is in the relay. Because some of these diodes may  have 
> failed due to the excitement of past  ESD events, how would I  check to see which 
> ones were ok?  Would the Diode checker on my fluke check  a circuit which had 
> both a coil and a diode - I;m assuming they would be  parallel.
>  
> Or is this whole line of reasoning nuts? Should I go back to idea of  
> stocking up on 100 volt caps and replacing all of them the next time one  fails?
>  
> 73   AI4TO  John Ferguson M/V   Arcadian
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