[sdiy] JFET input protection

[Scott Nordlund]

>> ESD is typically a very small charge at high potential.
>
>> A JFET has quite high gate impedance, so very high voltages can build up
>> and ruin things.
>
> Yes, when you discount the parasitic gate->source diode. What if you take
> it into account, though?

I guess it's reverse breakdown that causes the problem. Maybe you'd only 
need one clamping diode, then.

> What happens in a jfet once the breakdown voltage is exceeded? Is it
> simply the high current that destroys the device or is any "significant"
> current enough to permanently damage it?
>
> Antti

Well, I don't know all the details here, but JFETs (and plenty of other 
diodes and things, like GaN LEDs) are considered ESD sensitive, though
probably less so than MOSFETs.  Reverse breakdown isn't necessarily 
harmful, but maybe in these cases the sudden discharge causes local 
heating which creates defects or causes materials to migrate, leading
to degraded performance...or something.

I did study some semiconductor physics, but this goes a bit too deep
for me.  The only failure modes I can recall were electromigration and
hot carrier injection- related to aging and use over time, not things 
that aren't supposed to happen in the first place.
 		 	   		  
_________________________________________________________________
Hotmail is redefining busy with tools for the New Busy. Get more from your inbox.
http://www.windowslive.com/campaign/thenewbusy?ocid=PID28326::T:WLMTAGL:ON:WL:en-US:WM_HMP:042010_2