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FETs - plain'n'simple


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5/9/2000 11:06 PM
MikeB
FETs - plain'n'simple
For those that like to have simple info to hand when debugging circuits:  
http://ourworld.compuserve.com/homepages/g_knott/elect247.htm  
 
MikeB
 
5/9/2000 11:24 PM
aron

That's great Mike!  
 
I will add it to my site!  
 
Thanks,  
 
Aron
 
5/10/2000 1:57 PM
Rob

Most of the comments made on the site are pretty good but the one that says 'the FET is correctly biased' isn't quite correct. You need to do at least as much as the comments prior to this statement but it still doesn't ensure the FET is correctly biased.  
 
- You need to ensure Vgs is correct for the desired input levels and the FET concerned.  
- You need to ensure the drain resistor gives a proper drain voltage. For example in the example given the drain current is 1V/4.7k = 212uA. Thats going to develop 212uA*100k=21.3V across the drain resistor. So you will need a 25V supply rail for that circuit to work. With a 9V rail the FET is more or less saturated.  
 
Regards  
Rob
 

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