OPERATION OF TRANSISTOR AS A SWITCH


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The most important application of a transistor is to control the flow of power to another part of the circuit during the cutoff or saturation mode the transistor can create the binary on/off the effect of a switch. Switching is an important feature of a transistor, transistors in digital IC’s will work as a switch to reduce the power consumption
A circuit which can turn ON or OFF the electrical current is called as a switching circuit it operates in saturation and cutoff region when it is saturated, from collector to emitter it is like a closed switch and when it is cut off it is like an open switch

The main application of transistor is to switch ON and OFF DC output solid state switches are used for this

The devices which have High power such as solenoids or lamp requires more power than that of the ordinary supply and in that case, transistor switches are used
Transistor can operate as a switch in two areas the saturation region and cutoff region and by this, we could avoid the Q- point biasing and the voltage amplification is done by the voltage divider circuit so thus we could use the transistor as a switch in its cutoff (full off) or saturation (full on )

OPERATING REGION FOR TRANSISTOR AS A SWITCH

CUTOFF REGION

In this condition the transistor has zero base and collector input current and collector voltage is high and due to this large depletion region will be formed and no current flow through the device and it will be in fully off condition

Characteristics
• Base and input are grounded
• Base-collector and the base-emitter section is reverse biased
• Transistor will be in fully off condition
• There will be no collector current and the transistor operates as an open switch

SATURATION REGION AND CHARACTERISTICS

In this condition the transistor will be biased and therefore the base and collector current will be maximum and the collector-emitter voltage will be low and thus the depletion layer will be small and the flow of maximum current through transistor will be done and thus it will be in full on state
• Base and input is connected to VCC
• Base-emitter and base-collector junction is forward biased
• Transistor will be fully on
• Maximum current flows and the transistor will operate as a closed switch