Project Report Touch Switch


Acknowledgement

Aim

Introduction

Bipolar Transistor Configurations

The Common Emitter Configuration

Transistor as a Switch

Material required

Circuit Diagram

Working

Resources


Acknowledgement

I would like to express my special thanks of gratitude to my teacher (Name of the teacher) as well as our principal (Name of the principal)who gave me the golden opportunity to do this wonderful project on the topic (Write the topic name), which also helped me in doing a lot of Research and i came to know about so many new things I am really thankful to them.

Secondly i would also like to thank my parents and friends who helped me a lot in finalizing this project within the limited time frame.


Aim

Aim of this project is to demonstrate the working of NPN in common emitter configuration transistor as a switch.


Introduction

NPN Transistors are three-terminal, three-layer devices that can function as either amplifiers or electronic switches.

Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistor’s ability to change between these two states enables it to have two basic functions: switching or amplification.

Then bipolar transistors have the ability to operate within three different regions:

  • Active Region – the transistor operates as an amplifier and Ic = β.Ib
  • Saturation – the transistor is “fully-ON” operating as a switch and Ic = I(saturation)
  • Cut-off – the transistor is “fully-OFF” operating as a switch and Ic = 0

Three terminals are known and labeled as the Emitter ( E ), the Base ( B ) and the Collector ( C ) respectively.


Bipolar Transistor Configurations

As the Bipolar Transistor is a three terminal device, there are basically three possible ways to connect it within an electronic circuit with one terminal being common to both the input and output. Each method of connection responding differently to its input signal within a circuit as the static characteristics of the transistor vary with each circuit arrangement.

  • 1. Common Base Configuration – has Voltage Gain but no Current Gain.
  • 2. Common Emitter Configuration – has both Current and Voltage Gain.
  • 3. Common Collector Configuration – has Current Gain but no Voltage Gain.

The Common Emitter Configuration

In the Common Emitter or grounded emitter configuration, the input signal is applied between the base, while the output is taken from between the collector and the emitter. The common emitter amplifier configuration produces the highest current and power gain of all the three bipolar transistor configurations. This is mainly because the input impedance is LOW as it is connected to a forward-biased PN-junction, while the output impedance is HIGH as it is taken from a reverse-biased PN-junction.

In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing into the transistor as the emitter current is given as Ie = Ic + Ib. Also, as the load resistance (RL) is connected in series with the collector, the current gain of the common emitter transistor configuration is quite large as it is the ratio of Ic/Ib and is given the Greek symbol of Beta, (β). As the emitter current for a common emitter configuration is defined as Ie = Ic + Ib, the ratio of Ic/Ie is called Alpha, given the Greek symbol of α. Note: that the value of Alpha will always be less than unity.


Transistor as a Switch

To make the Base current flow, the Base input terminal must be made more positive than the Emitter by increasing it above the 0.7 volts needed for a silicon device. By varying the Base-Emitter voltage Vbe, the Base current is altered and which in turn controls the amount of Collector current flowing through the transistor. When maximum Collector current flows the transistor is said to be Saturated. The value of the Base resistor determines how much input voltage is required and corresponding Base current to switch the transistor fully “ON”.


Material required

Transistor:- Transistor is a semiconductor device that can both conduct and insulate. A transistor can act as a switch and an amplifier.

  • A transistor is a three terminal device. Namely,
  1. Base: This is responsible for activating the transistor.
  2. Collector: This is the positive lead.
  3. Emitter: This is the negative lead.

Resistor:- The resistor is a passive electrical component to create resistance in the flow of electric current.
LED:- An LED produces light when electricity flows through.
Battery:- A 9V dc battery is used to power this circuit.
Battery snap connector:- To connect the battery terminals to the rest of circuit.
Soldering Iron:-  To solder the various components used in this project.


Circuit Diagram

touch-switch-circuit-diagram


Working

When we touch the given points on the circuit transistor goes from cut-off mode to saturation mode allowing all the current to pass through LED. In this process LED turns on thus detecting when we touch the given points in the circuit. As a result out circuit works as a touch switch.


Resources