The BJT is a bipolar junction transistor whereas MOSFET is a metal oxide semiconductor field-effect transistor. A BJT has three terminals namely base, emitter, and collector, while a MOSFET has three terminals namely source, drain, and gate. BJT’s are used for low current applications, whereas MOSFET is used for high power applications. JFET is used in small amplifiers, electronic switches, digital circuits, sensitive circuits where very low noise is mandatory but MOSFET is used in Motor speed control circuits, power amplifier circuits, etc where high-speed switching is mandatory. MOSFET vs JFET JFETs can only be operated in the depletion mode whereas MOSFETs can be operated in either depletion or in enhancement mode. In a JFET, if the gate is forward biased, excess- carrier injunction occurs and the gate current is substantial. The following figure shows how a practical MOSFET looks like. Construction of a MOSFET. The construction of a MOSFET is a bit similar to the FET. An oxide layer is deposited on the substrate to which the gate terminal is connected. This oxide layer acts as an insulator (sio 2 insulates from the substrate), and hence the MOSFET has another name. P-Channel MOSFET Basics. A P-Channel MOSFET is a type of MOSFET in which the channel of the MOSFET is composed of a majority of holes as current carriers. When the MOSFET is activated and is on, the majority of the current flowing are holes moving through the channels.
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Field effect transistors, FETs come in a large variety of different types. Each type of FET has its own circuit symbol, so it helps to understand the different types of FET and their circuit symbols to enable the circuits to be read accurately.
Basic Mosfet Circuits
Junction FETs or JFETs were the first type of FET and these have a distinctive symbol showing the diode junction. Insulated gate FETs, including MOSFETs have circuit symbols that indicate the insulation on the gate.
Obviously dual gate FETs have two gates and both need to be incorporated into the circuit symbol.
Jfet And Mosfet Characteristics
| FET Circuit Symbols | |
|---|---|
| FET Type | Circuit Symbol |
| J-FET N channel | |
| J-FET P channel | |
| Basic enhancemment insulated gate FET (MOSFET) N channel | |
| Basic enhancemment insulated gate FET (MOSFET) P channel | |
| Basic enhancemment insulated gate FET (MOSFET) N channel no bulk semiconductor | |
| Basic enhancemment insulated gate FET (MOSFET) P channel no bulk semiconductor | |
| Basic depletion insulated gate FET N channel | |
| Basic depletion insulated gate FET P channel | |
Note: The circuit symbols for FETs are marked with D, G and S for drain, gate and source. These letters are not normally included in circuit diagrams, but they are included here for clarity and explanation.
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