Lab 17 RS
The JFET (Junction Field Effect Transistor n-channel)
1). Complete the table below for the JFET.
|Zero-Gate-Voltage Drain Current||2.0||20||mAdc|
|Gate-Source Cutoff Voltage||-||-8.0||Vdc|
|Total Device Dissipation @||350||mW|
|Forward Transfer Admittance||2000||7500||mhos|
2.) Construct the JFET circuit below.
3.) Plot measurements of -vs- by varying for = 0, 0.5, 1.0, 1.5 V. (40 pnts)
I have used the following resistors:
Below is the table with my measurements of voltagesand and calculation of the current . Here I have used the meter to measure directly the voltage drop between the drain and source and to measure the voltage drop on resistor .
So my calculated current becomes:
And below I have plotted four curves as function of for four different values of
4.) Plot -vs- (30 pnts)
For every measuredvalues I have picked up the current values in the middle of saturation region of each line as follow:
And below is my plot of -vs- :
5.) Calculate for your JFET (20 pnts)
For common source configuration JFET:
So to calculatewe need to know the functional dependence of . Lets approximate this function by line using my measurements and plot above:
The line equation is:
Also note that this line equation was obtained using about the same voltagein saturation region from my first measurements of as function of for four different values of . So we can take the partial derivative of with respect to using the line equation above. Finally,
Does depend on ? (10 pnts)
No. As we can see from calculation aboveis constant and does not depend from . That is true if we are working in saturation region where the functional dependence of with respect to is line so
If we are in active region ofas function of the functional form of with respect to is not the line anymore and will depend on .