Introduction to Transistors

Transistors are fundamental semiconductor devices that control current flow. Bipolar Junction Transistors (BJTs) and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) dominate with distinct characteristics and applications.

BJTs are current-controlled devices where a small base current controls a larger collector-emitter current. They consist of three regions: emitter, base, and collector, and operate in active, saturation, and cutoff regions.

MOSFETs are voltage-controlled devices with high input impedance. Gate voltage regulates electron flow through a channel between source and drain. They have enhancement or depletion modes, with the former being more common in digital circuits.

MOSFETs generally offer faster switching speeds than BJTs. This is due to their voltage-driven operation which induces less capacitance and thus quicker response times, making them suitable for high-frequency applications.

BJTs can handle higher currents but dissipate more power, making them advantageous in analog and power applications. MOSFETs, while less robust in current handling, are more efficient with power dissipation, fitting for digital and low-power uses.

MOSFETs typically exhibit better thermal stability compared to BJTs. BJTs have a negative temperature coefficient, leading to thermal runaway risks. Conversely, MOSFETs' positive temperature coefficient promotes self-stabilization, enhancing reliability in varying temperatures.

MOSFETs require less power to operate due to their high input impedance, needing only a voltage to switch states. BJTs consume more power since they require a base current, which can be a disadvantage in battery-powered devices.