Transistor as a Switch Experiment PDF

## **EXPERIMENT NO: 1** ## **TRANSISTOR AS A SWITCH** **Aim:** To verify the switching characteristics of a Bipolar Junction transistor. **Components & Equipment Required:** | S.No | Device | Range/Rating | Quantity in No. | |---|---|---|---| | 1 | TRANSISTOR (SL) – 100 NPN | - | 1 | | 2 | LED...

## **EXPERIMENT NO: 1** ## **TRANSISTOR AS A SWITCH** **Aim:** To verify the switching characteristics of a Bipolar Junction transistor. **Components & Equipment Required:** | S.No | Device | Range/Rating | Quantity in No. | |---|---|---|---| | 1 | TRANSISTOR (SL) – 100 NPN | - | 1 | | 2 | LED BULB | 5 VOLTS | 1 | | 3 | RESISTOR - 1 | 4.7KΩ | 1 | | 4 | RESISTOR - 2 | 470Ω | 1 | | 5 | POWER SUPPLY (DC REGULATOR) | 0-30V | 1 | | 6 | WIRES | - | - | | 7 | FUNCTIONAL GENERATOR | 3MHz | 1 | | 8 | BREAD BOARD | - | - | | 9 | DIGITAL VOLTMETER | 0-2/20/200V | 1 | **Circuit Diagram** [Description of a circuit diagram of a transistor with an LED.] **Theory** Bipolar Transistors are current regulating devices that control the amount of current flowing through them in proportion to the amount of biasing voltage applied to their base terminal. In a transistor, the base current directly controls the collector current. In the cut-off region of a transistor, the base voltage is less than 0.7 V. The base current is negligible. So the collector current Ic is also negligible. But the collector to emitter voltage Vce is maximum which creates a large depletion region and no current flows through the transistor. Hence this region is called as cut off region. When the transistor is in Saturation region, the maximum base current is applied that results with high collector current and lower collector to emitter voltage. And this results a lower depletion region layer. By this large amount of current can flow through the transistor. When the base bias voltage is lower than 0.7 V the transistor operated in the cut-off region. But when the base bias voltage increases from 0.7 V the base saturates the collector and the current starts to flow. In this state the transistor acts as a closed switch. The base resistor is not connected to the Vce in the off state of the transistor. For an NPN transistor, a positive voltage at the base will drive the transistor to the saturation region. **Procedure:** 1. Set up the circuit after testing all the components and probes. Set Rb= 470Ω, Rc=4.7ΚΩ 2. Connect the Function generator to the base resistor by setting the square waveform of amplitude 5 V p-p. 3. Observe the status of the LED and the output voltage waveforms in CRO. **Observation:** The LED was lit. When the voltage was increased, there was an increase in the intensity of the Light emitted by the LED and vice versa. When a connector was provided from the collector to the base, the transistor was conductive thereby acting as a switch and turning off the LED. Upon disconnection of the wire, the transistor was non-conductive and so the LED was turned on. **Result:** The circuit has been successfully implemented and the output has been verified. When the base voltage is high, transistor is turned on, and current flows from collector to emitter. When voltage is low, transistor is turned off and no current flows through it. Transistor acts as a switch in saturation and cutoff. | Components | Marks | |---|---| | Exp(10) | A | | Result(5) | A | | Record(5) | A | | Viva(10) | A | | Total(30) | - |