[sdiy] Does Source = Drain???

[ASSI]

On Sunday 13 June 2010, David Ingebretsen wrote:
> I was building the VCO core for my Steiner project and I
> inadvertently swapped the drain and source on the JFET. The
> circuit still worked. I re-read about JFETS, but didn't find a
> satisfactory answer. Can the Drain and Source be swapped in any
> circuit? That is, are they essentially the same electrically?

If it's a diffused JFET and they aren't playing any games with 
connecting something else to any pin, source and drain should be 
interchangeable with absolutely no differences.  This is also true of 
small signal MOSFET, however you will usually find that the source has 
been tied to the body, thus orienting the device.  Almost all power 
MOSFET are truly asymmetrical devices with very different drain and 
source constructions, also the source-to-body tie usually happens 
right in the device rather than being a double bond to the source pin.


Achim.
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