# Calculation of drain current in JFET simulate this circuit – Schematic created using CircuitLab

If IDSS= 10mA and Vp= -5V, when VDS=Vp, what is the value of ID and VGS?

Lets say I apply KVL on drain-source loop.

Then I get VDD-IDRD-VDS=0.

Substitute the value then I get ID=2.1x10-3. After that, I apply Solve the formula and get VGS=2.71V

Is the method I used correctly in solving this question?

• But in your schematics, Vgs voltage is equal to Vgg thus Vgs = -1V – G36 Jun 21 '20 at 19:05
• You have to make a design choice of the required Vds to determine the Id. 5V would be a reasonable value giving 0.5mA. – Kevin White Jun 21 '20 at 19:24
• You're in the "just applying formulas" mode without looking at the circuit to see what actually is happening. As G36 comments, there's a Vgs applied. What does that Vgs mean for the JFET? – Bimpelrekkie Jun 21 '20 at 19:27
• But isn't that there is a potential drop across the R1 resistor? Wouldn't this make Vgg not equal to Vgs? Or the resistor does not have effect on the circuit? – Nobu Nobu Jun 22 '20 at 14:02
• the normal method is to use KVL in GS loop and then use the current formula. Now you have two-equation and two unknown and you may find ID and VGS. – arsalan ghasemian Jun 23 '20 at 4:10