Aim

To understand the working of NOT gate using npn transistor and to design a circuit of NOT gate using npn transistor, LED, push button type toggle switches and suitable resistances.

Introduction

NOT gate is an Boolean operator based on the mathematical function of complement.

It works on digital signal as its input which have only two states of voltages, low as 0V and high as 5V.

NOT gate consists of electonic circuit of npn transistor having an input digital signal which can take r different combinations on voltages, for each two states of voltages there is a predefined output according to complement rule.

Apparatus used

Npn transistor (547 b)

Circuit board

Wires

9V battery and battery connector

LED (5mm, 1.5V)

Resistors

Push button type toggle switch

Push buttons

Theory and working

1.)Working of npn transistor in different configurations

2.)Understanding the functioning of NOT gate and its realisation

Realisation of NOT gate

3.)Circuit diagram used in making of NOT gate and its working

For first circuit

When the push button is in ‘released state’ then terminal ‘2’ is connected to terminal ‘3’, when push button is in ‘active or pressed’ then terminal ‘2’ is connected to terminal ‘1’.

When button is released then it is equivalent to zero base current. In this state, transistor is in cut-off mode no current flows through transistor, so whole current flows through LED.

When button is pressed then it is equivalent to high base current. In this state, transistor is in saturation mode, maximum current flows through transistor to negative of battery but does not flows through LED.

Conclusion

The output of NOT gate for different inputs clearly shows the expected output according to the truth table.

Sources of errors

Write yourself

Precautions

Do not connect any electronic component without resistance in series, it can burn the component.

Bibliography

NCERT textbook of class 12

Physics by S.L.Arora

Circuits available on internet