FET Drain Current Calculation
The relationship between the change in drain current ($\Delta I_D$) and the change in gate-source voltage ($\Delta V_{GS}$) in a Field-Effect Transistor (FET) is given by the transconductance ($g_m$):
$ \Delta I_D = g_m \times \Delta V_{GS} $
We are given:
- Initial drain current, $I_{D(\text{initial})} = 100 \text{ mA}$
- Initial gate-source bias, $V_{GS(\text{initial})} = -1 \text{ V}$
- Dynamic forward transconductance, $g_m = 0.25 \text{ S}$
- New gate-source bias, $V_{GS(\text{new})} = -1.2 \text{ V}$
Calculating Voltage and Current Changes
First, calculate the change in gate-source bias voltage:
$ \Delta V_{GS} = V_{GS(\text{new})} - V_{GS(\text{initial})} $
$ \Delta V_{GS} = -1.2 \text{ V} - (-1 \text{ V}) = -1.2 \text{ V} + 1 \text{ V} = -0.2 \text{ V} $
Next, calculate the corresponding change in drain current:
$ \Delta I_D = g_m \times \Delta V_{GS} $
$ \Delta I_D = 0.25 \text{ S} \times (-0.2 \text{ V}) = -0.05 \text{ A} $
Convert the change in drain current to milliamperes:
$ \Delta I_D = -0.05 \text{ A} \times 1000 \text{ mA/A} = -50 \text{ mA} $
Determining New Drain Current
Finally, calculate the new drain current by adding the change to the initial drain current:
$ I_{D(\text{new})} = I_{D(\text{initial})} + \Delta I_D $
$ I_{D(\text{new})} = 100 \text{ mA} + (-50 \text{ mA}) = 100 \text{ mA} - 50 \text{ mA} = 50 \text{ mA} $
The new value of the drain current is 50 mA.
Important Questions from Field Effect Transistors
FET is like a switched on condition when it operates in ______ mode.
Which of the following is the characteristic of Field-effect transistor?
When VDS is the drain voltage and VDS(max) is the maximum drain voltage, the JFET will breakdown if:
Which of the following is true about the transconductance of a MOSFET in saturation (I Dis the Drain Current)?
Transconductance in an FET indicates how effectively the input voltage controls the
