Transistor as a Switch

                                                       fig. Transistor as a switch

Solid state materials can be grouped in to 3 classes :- Insulators, Conductors and Semiconductors. Semiconductor material is neither conductor nor insulator. It has conductivity between conductors and insulators and is sensitive to temperature, illumination, magnetic field and minute amount of impurity atoms. This type of sensitive material for controlling or switching current is very much required in modern age. Today electronics device means present of semiconductor devices.

Semiconductor Devices are the foundation of electronics industry. For advance courses in electronics it is necessary to have basic knowledge of Semiconductor device. A common semiconductor device is a Transistor.

 

Aim of this project is to determine characteristic of a NPN transistor by varying base voltage and detect Cut-off Region and Saturation Region.
We have used a potentio-meter for varying Base voltage. After assembling the circuit use a digital multimeter and scale mark the voltage. You can also attach a multimeter permanently.
A low power indicator such as LED is used for detection of conductance of transistor. LED is connected to power supply through collector of transistor so that when transistor is conducted then circuit will be complete and led glows.
After making the project. Place the battery and start rotating nobe of POT. You will see LED starts glowing after reaching .5V and at .7V it will light Dark. Thus you can mark cut off region (fully off) and Saturation Voltage (full dark). Most of the transistor will conduct from .5 to .7 Volt.
This type of circuit is commonly used in voltage stabilizer for high voltage cut off. A relay is placed at LED connection.

Parts Used

NPN Transistor BC548

Resistance 1K and 220 Ohm

10K POT with knobe

LED and Battery Container

Transistor voltage (NPN )

1. As a switch: OFF = 0 to 0.3V, ON=0.7 V (Cutoff and Saturation Region )

2. As an Amplifier: 0.5 to 0.7V (Active Region)