ABSTRACT
Finally, to complete our discussion on transistors let us examine field effect and insulated gate bipolar transistors, or PET and IGBT. A common one used in many controller applications is the MOSFET, or metal oxide semiconductor field effect transistor. They are very similar to the silicon layer bipolar junction, but instead we vary the voltage (not the current) at the control terminal to control an electric field. The electric field causes a conduction region to form in much the same way that a base current does with bipolar types. The advantage is this: The controlling current, commonly called the gate current, sees a very high impedance c~ 1014Q) and thus we do not have to worry about proper biasing as we did regarding the base junction of our bipolar junction transistors. Figure 16 illustrates this difference.
