Metal Oxide Semiconductor Field Effect Transistor

Aim:

To study the V-I characteristics of MOSFET

Apparatus Required:

• MOSFET
• Bread board
• Resistor
• Two Voltage Sources
• Connecting Wires

Theory:

MOSFT stands for Metal Oxide Semiconductor Field Effect Transistor. It is actually a four terminal device whose substrate terminal must be always hold at one of the extreme voltage in the circuit either the most positive for PMOS or the most negative for NMOS. One unique property of MOSFET is that the gate drains no measurable current. The body of any N-channel MOSFET is made up of P-type material. 2 N-type materials are diffused at the top. A depletion region will be formed in the PN junction. A metal contact is made at the bottom of the P-type substrate and a terminal is taken out called the body or substrate. Similarly, a metal contact is made at the top of both the N-type materials, and two terminals are taken out as Drain and source. A Silicon dioxide layer is drawn in between the two N-type wells at the top. A metal contact is made at the top of it and a terminal is taken out called a Gate terminal. MOSFET is used as a high-frequency amplifier, brushless DC motor drives, electronic DC relays, inverter. The voltage at which the channel of the MOSFET closes is called the “pinch-off voltage”. When VDS  is increased beyond the pinch-off voltage, VGS  controls the channel current and VDS  has little or no effect i.e. remains constant.

Circuit Diagram:

Procedure :

Output/Drain Characteristics

1. Connect the circuit as per diagram properly
2. Keep V_GS constant at some value by varying V_GG.
3. Vary V_DS and measure the drain current I_D. Tabulate all the readings.
4. Repeat the above procedure for V_GS for different values

Transfer Characteristics

1. Connect the circuit as per given diagram properly.
2. Set the voltage V_DS constant at a particular voltage.
3.  Vary V_GS by varying V_GG and note down value of drain current I_D. Tabulate all the readings.
4. Plot the output characteristics V_DS versus I_D and transfer characteristics V_GS versus I_D.

Observation:

Output/ Drain Characteristics

VGS =		VGS =		VGS =		VGS =		VGS =
VDS(V)	ID(mA)	VDS(V)	ID(mA)	VDS(V)	ID(mA)	VDS(V)	ID(mA)	VDS(V)	ID(mA)

Transfer Characteristics

VDS =
VGS (V)	ID (mA)

Result:

Hence, when we apply and vary V_DS at constant V_GS then I_D increases and after some time it becomes constant.

Precaution:

1. The reading should be in multiple of least count.
2. For accuracy current should be taken in mA.