In which region transistors act as a switch?

Hint: Before we answer this question, let’s have a look at a transistor. It is a semiconductor device used to amplify the electrical signals and power. It is the basic building block in modern electronics.

Complete step by step solution:
The transistor consists of three terminals: emitter, base and collector which helps to connect to the required circuit in order to get output signals. The bipolar junction transistors are of two types, they are n-p-n transistor and p-n-p transistor. Transistor has mainly three regions of operation,
1. Active region
2. Saturation region and
3. Cut- off region

Transistor works in the active region normally. In both the other regions the transistor acts as a switch. Let’s find out this in detail. If the transistor should act like a switch, then it should be having 2 positions, ON and OFF.

Transistor will be in the OFF position (Cut-off region) when the input is set as zero. Because during this state, the transistor acts as an open circuit and the entire voltage will be available at the collector.

Transistor will be in ON position (saturation region), when a sufficient input voltage is given. Because during this condition, the collector-emitter voltage will be approximately equal to zero, that is the transistor acts as a short circuit. Thus, the collector current will flow and the output is obtained.

Remember that, whenever the input is given to the transistor it should always be to the base and the output is taken across the collector and emitter. When there is no base voltage given, the switch is off. When base voltage is applied, the switch is on.

Thus, the transistor acts as a switch in both saturation and cut-off regions.

Note:Depending on the structure, the transistors are mainly classified into two types, those are BJT (Bi-polar Junction Transistor) and FET (Field Effect Transistor), under FET we have two types- JFET (Junction Field effect Transistor), and MOSFET.