The working of the Transistors as a switch is explained here. When a transistor is used as an electronic switch, the transistor is operated in the cutoff and saturation region to open and close a circuit respectively. The working of transistors as a switch has an important role in digital electronics.
Working of the Transistors as Open Switch
In the cutoff region, both of the junctions Base-Emitter (BE) and Base-Collector (BC) are reversed-biased. As both of the junctions are reversed biased no current flows through the collector except leakage current. This mode of operation works as a turn-off switch. During the cutoff region, the supply voltage will drop across the emitter and collector terminals using the following formula:
Working of the Transistors as a Close Switch
In the saturation region, both the Base-Emitter BE and Base-Collector junctions are forward-biased. In this mode of operation, the transistor works as a short circuit between the collector and the emitter. The transistor can provide the IC (Sat) current when used in saturation mode.
Where the VCE(Sat) can be neglected as it is too small compared to VCC and the above formula will become:
To maintain the transistor in the saturation region a minimum base current IB is required and can be calculated using the formula:
Conclusion
The working of the transistors as a switch can be explained by the two states’ region. of operation
- Transistor as an open switch in the Cutoff region
- Transistor as a close switch in the saturation region
Short Answer Question:
How do transistors work as switches?
Transistors work as switches by controlling the flow of electrical current. In the on state, they allow current; in the off state, they block it.
What is a transistor as a switch circuit?
A transistor switch circuit includes a voltage source and a transistor. When a base pulse is applied, the transistor closes, allowing current, and opens when the pulse is disconnected.