JFET Voltages Question?

[modsquad]

I am trying to learn this stuff while debugging so bear with me.  Given the following parameters

OFF CHARACTERISTICS
Gate-Source Cutoff Voltage Min -.03  Max - 1.5

ON CHARACTERISTICS
Zero-Gate Voltage Drain Current 1.0

Does that mean that if I have a voltage of greater than 1.5v at source that the gate shuts off?  Also, What is the Zero Gate Voltage Drain.

I am thinking that I have too much voltage across the J201 FET I am using and shutting down the gate.

[Jay Doyle]

I would recommend reading at least the first application note on this page:

http://www.vishay.com/fets-small-signal/ssfanp/

The 'off' characteristic you quote is the voltage difference between the gate and the source that is needed to completely shut off current through the drain-source channel. The numbers are the range that a J201 will fall into. In other words you can get one J201 that has a Vgs(off) of -.3V and another of -1.5V and they can BOTH be a J201. That is the range that J201s have for that particular value and is one of the reasons FX built out of JFETs are so variable.

The 'on' characteristic you quote is the max amount of current the J201 will pass when the voltage on the gate is equal to the voltage on the source, or all the way 'on'.

In answer to your question, if the voltage at the gate is 0, then yes, all J201s will shut off if the voltage voltage on the source is 1.5V or greater, but it could be as low as -.3 for some samples.

Also, a little more info about what you are doing will probably allow us to help you a lot more. It is good to learn the theory, but in practice, something else, other than the JFET itself, is probably the issue.

Good Luck,

Jay

[modsquad]

See my debug note:

http://www.diystompboxes.com/smfforum/index.php?topic=48080.0