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FET comparison chart

 
   All About Circuits - Newsgroup Archive Forum Index -> alt.engineering.electrical


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Peter
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PostPosted: Fri Jun 08, 2007 7:47 am    Post subject: FET comparison chart

I've always been confused between JFETS, MOSFETS, Enhancement mode, etc...

Recently I did some reading and have a better understanding at the
differences. It appears JFETS are similar to BJTs, however, they have
higher input impedance and require negative voltage to turn off. MOSFETS
require 0 volts to turn off, and have high impedance.


All I'm pointing out is that I've done some research before I ask my
question.


Is there a comparison chart that shows all the variations between the
models? It seems MOSFETS require much less gate current than JFETS, but
each one has good and bad points.

It would be nice to see a chart laid out.


Thanks in advance.
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Salmon Egg
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PostPosted: Sat Jun 09, 2007 8:20 am    Post subject: Re: FET comparison chart

On 6/7/07 8:47 PM, in article 7MGdnau6vOv6TPXbnZ2dnUVZ_vbinZ2d@comcast.com,
"Peter" <private@private.com> wrote:

Quote:
I've always been confused between JFETS, MOSFETS, Enhancement mode, etc...

Recently I did some reading and have a better understanding at the
differences. It appears JFETS are similar to BJTs, however, they have
higher input impedance and require negative voltage to turn off. MOSFETS
require 0 volts to turn off, and have high impedance.


All I'm pointing out is that I've done some research before I ask my
question.

In all FETS, the input signal controls the cross section or conductivity of
the conducting channel. It how that is done that leads to all the FET
variations.

A JFET and BJT are completely different except for the material (usually
silicon) used to make them. The conductive channel width of the JFET is
controlled by reverse drive on the junction. In structure, it is somewhat
similar to a unijunction transistor.

Bill
-- Support the troops. Impeach Bush. Oh, I forgot about Cheney.
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1fine@itude
Guest





PostPosted: Sun Jun 10, 2007 8:00 am    Post subject: Re: FET comparison chart

Peter wrote on 07-06-07 20:47 :
[...]
Quote:
Is there a comparison chart that shows all the variations between the
models? It seems MOSFETS require much less gate current than JFETS, but
each one has good and bad points.

MosFETs don't require Gate current, unless you consider very high
frequency (Gate capacitance), hence the "Metal-Oxide-Semiconductor"
portion of the acronym. Junction FETs do require finite gate current.
Before you go further, decide what you mean by "good and bad".

Try undergraduate EE courses and class material, unless, of course,
Google is still down.
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