Comparing BJT and MOSFET Transistors in a Given Application

BJT Transistors in a Given Application

BJT (Bipolar Junction Transistor) transistors are three-pin devices available in two types: PNP and NPN.
BJTs are current-controlled devices; the base current (Ib) controls the collector current (Ic).
BJTs exhibit low input impedance because small changes in input current can result in significant changes in output current. This makes BJT less suitable for high impedance sources.
These transistors have high current gain, making them good for amplification applications.
Because BJT transistors handle less power and withstand lower voltages, they are often used in signal amplification tasks such as in audio equipment.
However, BJTs can suffer from thermal runaway because as the transistor warms up, it allows more current to flow, which further increases the device’s temperature.

MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistors are also three-pin devices, available in P-channel and N-channel types.
Contrary to BJT, MOSFETs are voltage-controlled devices, so the gate-source voltage (Vgs) controls the drain current (Id).
MOSFETs have high input impedance, allowing to handle high impedance sources with minimal loss of current.
These transistors have lower power dissipation, hence, suitable for switching applications such as power converters.
MOSFETs are also often used in digital circuits because their function is more analogous to that of a switch.
In contrast to BJTs, MOSFETs are more immune to thermal runaway due to their positive temperature coefficient. However, they are more sensitive to electrostatic discharge, necessitating careful handling and protection circuits when being used.

While BJTs are more suitable for small signal amplification due to their high current gain, MOSFETs are better suited for switching applications and digital circuits with their high input impedance and lower power dissipation.
The choice between a BJT and a MOSFET depends on the specific application, the required power handling, and whether a current- or voltage-driven device is more suitable.
Understanding the strengths and weaknesses of each transistor type is crucial in making an informed decision on which to use in a given application.