The power semiconductor transistor, such as a MOSFET, is a three-terminal device that is controlled by a gate terminal. By increasing the gate voltage the current in the transistor can be controlled. For a MOSFET, if the gate voltage is below a minimum level (called the threshold voltage, uG,th) then the MOSFET is off and no current flows. Once the gate voltage is above the threshold voltage then current can flow. Initially the MOSFET looks like a resistance between its drain and source and therefore exhibits an ohmic relationship between its drain current and drain-to-source voltage. If the current rises above a certain saturation level then the drain current becomes limited to that current level. Therefore the MOSFET characteristic looks like a voltage-controlled current source.

• Explore the input and output transfer characteristics of the MOSFET.
• Adjust the gate voltage and observe the change in current and operating characteristic.
• Adjust the drain-to-source voltage and observe the change in current.