JFETs are by bane of existence. I work with older audio gear, or gear specifically designed to have specific characteristic distortion profiles. I match JFETs rigorously to then place them in parallel. The common one for now is the Toshiba 2SK209GR. It's far underpowered for audio, hence we put them in parallel when matched!
I’m an electronics newbie. I’ve been copying the work of others to make regenerative radio receivers. The simpler circuits use a single JFET as both the RF amplifier and the audio demodulator. Amazing performance. Brilliantly clever idea. Credit to Edwin Armstrong who patented the discovery around 1915 (but using a thermionic valve where we can now use a JFET)
On the subject of MOSFETS having infinite gate impedance, and IGBTs for that matter. I often find that there is a series resistor of around 100 Ohms or so, put in series with the gate, particularly on power devices. Should the device go short circuit, the small resistance prevents destruction of the circuitry, PCB tracks and wiring connected to the gate. I service and repair welders, and there's usually a resistor in the gate connection for that reason.
Good tutorial. I have always had trouble with FETs or MOSFETs. I do have an unrelated question for you. I have a Lenovo laptop that has a short somewhere. I know where it is getting really hot, but I don't have a schematic. Replacing the main board is not an option as it costs more than if Just bought a new laptop though not one quit as expensive. It failed about 18 months after I purchased it and I did not purchase the extended waranty as my only other laptop I had was a Dell Inspirion 8100 which never failed in all the time I had it. In fact I still have it and it still works though it is really slow. So, I never thought about my new laptop failing. Can you help in anyway or should I salvage the screen and toss the rest of it. I really hate to do that though if there is some way I can fix it. I was an electronics tech for over 30 years though I have forgotten alot now that I am older, but I don't have any real test equipment other than several dvms, a super cheap $20 scope, power supply, and a digital thermometer.
Sorry, Don't know. Can I measure that using another multimeter across it in millivolts range or would that in itself affect the reading? Hmmm I guess there is only one way to find out...
i repaired a Fluke 8520A some time ago and it had a lot of JFETs they used them as switches if i remember correctly some JFETs was broken on it but the problem was i couldn't find any datasheet for them seems like they were in aircrafts for military etc so had to test a bunch of JFETs until it read right on the display lol
I haven't played with a JFET for a couple of decades now, so many thanks for the reminders. They are really useful devices.
Perfect blend of theory, practical and curiosity 👍
Thanks 🙂
JFETs are by bane of existence. I work with older audio gear, or gear specifically designed to have specific characteristic distortion profiles. I match JFETs rigorously to then place them in parallel. The common one for now is the Toshiba 2SK209GR. It's far underpowered for audio, hence we put them in parallel when matched!
My dream woman... 🤣🤣😉
@@mattstroker3742 Hah, why? Why's that? 😅😅
I’m an electronics newbie. I’ve been copying the work of others to make regenerative radio receivers. The simpler circuits use a single JFET as both the RF amplifier and the audio demodulator. Amazing performance. Brilliantly clever idea. Credit to Edwin Armstrong who patented the discovery around 1915 (but using a thermionic valve where we can now use a JFET)
Excellent!!
I never fail to learn something from one of your videos, thank you!
Why you apply positive voltage to Jfet gate?
Great video, thank you for sharing
Great explanation, Thank you. Paul, USA!
And thank you for the compliment
On the subject of MOSFETS having infinite gate impedance, and IGBTs for that matter. I often find that there is a series resistor of around 100 Ohms or so, put in series with the gate, particularly on power devices.
Should the device go short circuit, the small resistance prevents destruction of the circuitry, PCB tracks and wiring connected to the gate.
I service and repair welders, and there's usually a resistor in the gate connection for that reason.
Good tutorial. I have always had trouble with FETs or MOSFETs.
I do have an unrelated question for you. I have a Lenovo laptop that has a short somewhere. I know where it is getting really hot, but I don't have a schematic. Replacing the main board is not an option as it costs more than if Just bought a new laptop though not one quit as expensive. It failed about 18 months after I purchased it and I did not purchase the extended waranty as my only other laptop I had was a Dell Inspirion 8100 which never failed in all the time I had it. In fact I still have it and it still works though it is really slow. So, I never thought about my new laptop failing. Can you help in anyway or should I salvage the screen and toss the rest of it. I really hate to do that though if there is some way I can fix it. I was an electronics tech for over 30 years though I have forgotten alot now that I am older, but I don't have any real test equipment other than several dvms, a super cheap $20 scope, power supply, and a digital thermometer.
They are also often integrated inside of microphones or as first stage amp.
12:16 - Richard, what is the burden voltage for this meter in the μA range?
Sorry, Don't know. Can I measure that using another multimeter across it in millivolts range or would that in itself affect the reading? Hmmm I guess there is only one way to find out...
Some Power JFETs still available (United Silicon Carbide / Qorvo UJ3N), but expensive and mainly used in specialist areas (motor drives, heating etc).
Thanks for the info
i repaired a Fluke 8520A some time ago and it had a lot of JFETs they used them as switches if i remember correctly
some JFETs was broken on it but the problem was i couldn't find any datasheet for them seems like they were in aircrafts for military etc so had to test a bunch of JFETs until it read right on the display lol
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