The path taken by an electric current in flowing through a conductor through one complete run of a set of wires from a power source, such as a panelboard, to various electrical devices and back to the same power source. The wires used for various circuits are prescribed by codes, such as the National Electrical Code.
Transistors are basic to the operation of electronic circuits. Bipolar transistors have three terminals, designated as the base B, the collector C, and the emitter E. These terminals connect to two diode junctions, B-C and B-E, these forming back-to-back diodes. The B-E junction is often forward-biased, in which case its voltage is about 0.7 V, while the B-C junction is reverse-biased for linear operation.
The MOSFET is a versatile device, acting as a voltage-controlled current source in the saturation region and approximately as a voltage-controlled resistor in the resistive region. It can also be electronically controlled between cutoff and the resistive region to make it act as a switch, while for small signals around an operating point in the saturation region it acts as a linear amplifier. Another feature of the MOSFET is that, besides the categories of n-channel and p-channel devices, there are also enhancement- and depletion-mode devices of each category. In practice, for electronic circuit considerations, an n-channel device has Vth > 0 for enhancement-mode devices and Vth < 0 for depletion-mode devices, while the signs are reversed for p-channel devices.
Often, though, they are used for other purposes, such as to route signals in logic circuits. Transistors can be considered the workhorses of modern electronic circuits, and consequently many types of transistors have been developed, among which the most widely used are the bipolar junction transistor (BJT), the junction field-effect transistor (JFET), and the metal oxide silicon field-effect transistor (MOSFET).