![]() So, when the transistor moves into the ‘ON’ condition, there will be a flow of current from the source terminal to the ground via load. In this switching method, the connected load in contact with the switching point where this acts as a reference point. In the same way, when there is no voltage applied at the input terminal, then the transistor functions in the cut-off region and functions as an open circuit. So, the transistor in this condition performs as a switch and the current that flows through the collector is considered as the transistor current. When there is a good amount of voltage which is ~0.7V in between the emitter and the base edges, then the flow of voltage at the collector to emitter edge is zero. In addition, the working of transistor as a switch can be explained in detail as below:ĭepending on the applied voltage value at the base edge of the transistor, switching functionality takes place. When the voltage at the collector-emitter junction is ‘0’, this means ideal saturation condition.The voltage value at the emitter-collector junction, and at output terminals is ‘0’.The current flow in the collector terminal is Ic = (Vcc/RL).The base-collector junction is in forward biased condition.When the transistor is completely OFF, it moves into the saturation region.Here, the transistor functions as a CLOSED switch.The base-emitter junction is in forward biased condition.The voltage level at the base-emitter junction is more than 0.7v.Both the base and input terminals are connected to Vcc = 5v.This is the working of the transistor as a switch. For a PNP transistor, the Emitter potential must be +ve with respect to the Base. The definition of “saturation region” or “ON mode” when using a bipolar NPN transistor as a switch as being, both the junctions are forward biased, IC = Maximum, and VB > 0.7v. Therefore the transistor is switched “Fully-ON”. At this condition, the depletion layer becomes as small as the possible and maximum current flowing through the transistor. In this region, the transistor will be biased so that the maximum amount of base current(IB) is applied, resulting in maximum collector current(IC=VCC/RL) and then resulting in the minimum collector-emitter voltage(VCE ~ 0) drop. The voltage value at the emitter-collector junction, and at output terminals is ‘1’.There will be no flow of current in the collector terminal which means Ic = 0.The base-collector junction is in reverse biased condition.When the transistor is completely OFF, it moves into the cut-off region. ![]()
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