uh uhm

j fets mhm

So im bored thus there will be an article for the sake of my own self entertainment. Primarily these arent really used anymore, therefore it becomes very interesting to do so.

How do i operate them?

Drain

Every potential must be on the positive polarity.

Dont exceed the voltage limit of the datasheet.

The same goes for the current, which would flow through the entire component.

Gate

All potentials here must be on the negative polarity.

is voltage drive (in case you confuse them with bjt)

the voltage(increase) will increase the components resistance. The datasheet provides a Vgs curve for that. If it doesent, tell em theyr retarded.

in order to prevent charge buildup a high ohm resistor is placed from gate to GND.

Additional Vgs :

There are different regions

linear

low voltages are applied at gate and drain.

The Vgs trace acts "linear" in this region, this means it can predictably used for linear controling a signal

Transition region

will have an asymmetric effect on the signal. the lower signal (negative) polarity will be lower in amplitude

Active region

the applied voltage will vary the components resistnace, yet the current changes will be more minimal than in other configurations.

Source

Sits on GND, or has a small resistor between it.

Additionally

Choose an appropriate Drain resistor - i usually just

make sure the watt handling of the j-fet is not blown - give it a margin for failuer. VxA = W

the highest resistance the device has (as of te highest value Vgs) should be deciding the drain resistor aswell.

This ensures you have enough range to change potential differences.

Default resistance - R(Vgs-0) = 100ohm. ← as an example, every jfet has its internal resistance, this can be overcome by a slight counter bias on the gate. Vgs positive, by a small amount. Test it yourself, often this is not specified in the datasheet and can lead to breakdown if done wrongly. Else i advise to buy a jfet with lower R(Vgs-0) if there is need.

Avalanche - if your retarded

ever been to sierra. sierra nevada.

when your j fet runs hot and eventually starts to decrease in resistance, one may experience such. How its prevented ? A resistor at the source, and the one at the drain. The gate should usually have such high impedance that it wont need one (unlike a bjt).

But lets assume the entire thing gets hot, -not even because you designed the biasing wrong, but due to external interference.

The term avalanche refers to current shooting through it hence. The power rating AV will be exceeded and the device is shot through.

So yea nevada is cool.

Thats pretty much it