Transistors can be found in both the digital and analogue domains because they are widely used in a variety of applications such as switching circuits, amplifier circuits, power supply circuits, circuits such as digital logic, voltage regulators, and oscillator circuits are examples.

The transistor, as one of the most important electronic devices, has found use in a wide range of applications, including embedded systems, digital circuits, and control systems.

Transistors are three-layer, three-terminal semiconductor devices that are commonly used in signal amplification and switching. This means we can ignore the operating Q-point biasing and voltage divider circuitry required for amplification and simply drive the transistor back and forth between its “fully-OFF” (cut-off) and “fully-ON” (saturation) regions, as shown below. The Saturation Region and the Cut-off Region are the areas of operation for a transistor switch. If the circuit employs a bipolar transistor as a switch, the blessing of the transistor, either NPN or PNP, is configured to operate the transistor on both sides of the previously discussed ” I-V ” characteristics curves. However, high-power devices such as motors, solenoids, or lamps frequently require more power than an ordinary logic gate can provide, so transistor switches are used. Solid-state switches are one of the most common applications for using transistors to turn a DC output “ON” or “OFF.” Some output devices, such as LEDs, require only a few milliamps at logic level DC voltages and can thus be directly driven by the output of a logic gate. However, by biassing the transistor’s Base terminal differently than for a signal amplifier, both NPN and PNP type bipolar transistors can be made to operate as “ON/OFF” type solid-state switches. When used as an AC signal amplifier, the transistor’s base biassing voltage is applied in such a way that it always operates within its “active” region, i.e., the linear part of the output characteristic curves.

Transistor as a switch download