#1186 2N5457 JFET Applications

Comments · 249

• RI

  @richardballinger517 · 3 days ago

  Best example of how a JFet works I've seen.

• UR

  @urlkrueger · 4 years ago

  An interesting continuation of this would be to expand on your discussion of distortion by using a spectrum analyzer to show the effects at different operating points.

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• RI

  @rickwise9910 · 4 years ago

  You know you're listening to an optics guy when he says that's the "cyan trace." :-)

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• MA

  @markcummings150 · 4 years ago

  It’s been over 30 years since I learned how JFETs work and I’ve never used them since, so I had forgotten how they work and why I’d need them. Thanks for the refresher course and also what type of circuit you would use them in.

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• HO

  @homemdosaco2000 · 4 years ago

  Too much nitpicking in this video&apos;s comments.<br>I learned something; thanks for sharing.

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• TE

  @TechProbe · 4 years ago

  Thanks for the easy approach to understand the JFET characteristics by showing us its circuit under operation !

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• ST

  @stamasd8500 · 4 years ago

  There are depletion mode MOSFETs which act aomewhat like JFETs, at least in part of their characteristic. They are fairly rare and not much used, but they do exist. One nice property of those is that, as opposed to a JFET, you can allow the gate to swing to a positive voltage, not only negative. Because it&apos;s not a junction, and it won&apos;t become directly biased if it gets positive. <br>As for choosing JFETs for an application - in my type of applications (voltage-controlled current sources mostly) I start by looking at JFETs with an Idss (drain current when Vgs=0) in the range that I am interested in. Idss also happens to be the maximum current that the JFET will conduct. Everything flows from that point on.

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• CH

  @ChrisSmith-tc4df · 4 years ago

  One interesting use for these are packaged as 2-lead devices and called current regulating diodes. They&apos;re sorted by their nominal current into part numbers.

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• GR

  @grantlack · 4 years ago

  &quot;I chose this particular JFET transistor because I have a lot of them, and it&apos;s a very very very common one.&quot; or was, until it went very very very EOL.<br>Central is still selling them, but naturally it&apos;s at their &quot;where else are you gonna go?&quot; prices.

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• 10

  @100amps · 4 years ago

  Wow. This was perfect for me. I&apos;m a tube amp guy so this was cool. These things work like tubes, with the obvious differences of course. Looking forward to &nbsp;watching more of your videos.

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• BO

  @bobkozlarekwa2sqq59 · 4 years ago

  Also a very easy circuit to do impedance matching. Common use is to allow a very high impedance microphone, like D-104, to be used with modern day transceivers that use lower impedance microphones. I used a 10M ohm resistor from the input to ground to accommodate the D-104 microphone.

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• SA

  @sashareinhard6645 · 3 months ago

  the ACTUAL math for the gain is very nice: for small signals u can model the jfet&apos;s source as a resistor with a transresistance of r_e=1/g_m, applying the change in input to the top of the r_e resistor. looking at the graph, g_m is about 15mS so r_e = 666.66 ohms. now our circuit is all resistors and is super easy. the small signal current is i_d = v_in * (666.66 ohm + 270 ohm), and so the small signal output is v_out = i_d * 10k ohms = 10.68 v_in. so gain of 10.68. there wasnt any shortcuts here, this is how its done

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