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August 13th 04, 05:42 PM

John Larkin

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On Fri, 13 Aug 2004 03:49:15 +0000 (UTC),
(Ken Smith) wrote:

In article ,
Fred Bloggs wrote:

John Larkin wrote:

Looks like the jfet will be saturated with the values shown, not good
for RF work. Looks like he got the sign of Vgs backwards. The next
example on the same page illustrates that Vg must be near zero, not
+5. Really silly, putting these two circuits side-by-side.

John

Shhhh...don't tell the resident idiot, but it's going to be damn tough
biasing that IDSS=5mA JFET to a quiescent ID=10ma....

Theres no problem getting 10mA to flow in a FET with Idss of 5mA. Just
apply a positive bias to the gate. I've had as much as 2 or 3 A flow
through a JFET this way.

Jfets make pretty good pA-leakage diodes, although the series
resistance tends to be higher than for a "real" diode. Never tried one
as a power rectifier.

Jfets don't enhance much, but gaasfets - especially phemts - enhance a
lot, typically 1.6 * Idss just before the gate begins conducting in
earnest. That can be useful.

John

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