This document describes designing a NOT gate circuit using an npn transistor. It explains the working of the NOT gate by complementing input signals of 0V and 5V to produce the opposite output voltage. The circuit uses an npn transistor, LED, resistors, battery, and toggle switches. Pushing the button simulates a high input, causing the transistor to saturate and current to bypass the LED, turning it off. Releasing the button simulates a low input, causing the transistor to cut off and current to flow through the LED, turning it on. The output was verified using a truth table to operate as a NOT gate.

1. 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.

2. 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.

3. 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

4. Theory and working
1.)Working of npn transistor in different configurations

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

7. Realisation of NOT gate

8. 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’.

9. 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.

10. 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