![]() In given below circuit transistor is used as switch for on and off bulb.So we discuss such circuits that used transistor as a switch, for an explanation of such circuits we use NPN transistor. ![]() Due to this feature, it mostly used in different electronics circuitry as a switch.The structure of a transistor is such that collector current will not flow until there is no source of current at base.As Ic=ßIb so due to zero value of base current the collector current also zero and it behave like an open switch.To open the terminals of switch we remove the current passing through the base.You can see that terminal of switch that are collector and emitter are closed and bulb is illuminating as a large collector current flowing through it.So, in this case, resultant circuit can be constructed as. In the above figure, you can see that emitter is at ground potential so we can also suppose that collector is also zero potential.The value of collector current will be larger if the resistance between collector and emitter is almost zero.This source provides large amount of base current due to that collector current flows in the collector and emitter circuitry.For closed the switch the battery is connected between base and emitter terminals.The base and emitter of transistor working as a controller that decides open and closed condition of switch.A circuit that consists of the bulb as load is connected with the collector and emitter terminals of transistor.In this circuit, NPN transistor is used as a switch its collector and emitter is points are working as terminals of switch.For a practical understanding of transistor as a switch we discuss a circuit that is shown in a given figure.In the case of PNP, the emitter should be connected with a positive terminal of battery.In a simple way, we can define saturation region as it will occur when the current flows through the collector are extreme and the voltage across base terminals is 0.7 volts it is for NPN transistor.The value of the voltage at collector and emitter terminals will be zero so there will be no depletion layer and a large amount of current will passes through the transistor and it behaves like a closed switch.In this portion, the transistor will have such biasing that the amount of current at base terminal is maximum that causes to flow extreme current through the collector.So the transistor is completely off meant it is an open cirucit.The value of voltage across the collecter and emitter terminals (VCE) is higher that cause to make larger depletion layer in the transistor and zero current flows through the component.In this operation region of a transistor the value of current at base is zero (IB=0) so the value of current at collector will also 0.Let's discuss these two regions of transistors with detailed. In this curve you can see that the portion at the below of curve has pink colour is denoted as Cut-off portion and blue colour portion is known as saturation portion of the transistor.In the given figure the current and voltage characteristics curve is shown.Now we discuss these three regions one by one with detailed.But in other 2 regions that are saturation region in which transistor is in on state and cut-off region in which transistor is off, work as a switch.In the first region that is active regions, transistor operates as an amplifier.There are 3 regions in which transistor operates the first one is active, second one is saturation and third one is cut-off region.For understanding the working of a transistor as switch we use bipolar junction transistor ( BJT) and will construct its current versus voltage curve.So let's get started with Transistor as a Switch. In today's post, we will discuss how we can use a transistor as a switch and also see its practical working in different circuits. Most transistors are constructed from silicon and germanium but other semiconductor materials are also used for construction of transistors. Depending on doping level transistors are classified into 2 types first one NPN and the second one is PNP transistor. It also used in different engineering projects and circuitry. It was created by William Shockley (who was a physicist of United States of America) in 1947. In today’s tutorial, we will have a look at Transistor as a Switch. The transistor is a 3 pin semiconductor module used for different amplifier and switching circuits. Hello friends, I hope you all are doing great. ![]()
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