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NOT Logic Gate with Transistor

 

Creating a NOT gate using transistor is a fundamental exercise in digital electronics. In this post, I will guide you through the process of building a NOT gate with transistor, explaining each step in detail.

 

What is a NOT Gate?

A NOT gate is a basic digital logic gate that outputs TRUE or HIGH (1) when input is FALSE or LOW. And LOW if input is HIGH. The truth table for a NOT gate is as follows:

Input

Output

0

1

1

0

 

Components Needed

To build a NOT gate, you will need the following components:

  1. NPN Transistors: BC547 (1 No.); Q1.
  2. Resistors: 10K (1 No) - R1.
  3. Resistor: 300E (1 No) – R2.
  4. Resistor: 470E (1 No) – R3.
  5. LED: 5mm Red (1 No) – L1, for output indication.
  6. Switches: Tact Switch/ push button (1 No) – S1.
  7. Power Supply - DC source, +5V, Vds.
  8. Breadboard & Wires - for assembling the circuit

 

Understanding the Circuit

In a NOT gate circuit with NPN transistors, one transistor is used. The output is taken from the Collector of the transistor. The base of the transistor is connected to the input through a resistor, which limits the current and prevents damage to the transistor.

 

Transistor Basics

  • Emitter: The terminal through which current leaves the transistor.
  • Base: The terminal that controls the transistor's switching.
  • Collector: The terminal through which current enters the transistor.

For an NPN transistor, when a small current flows into the base, it allows a larger current to flow from the collector to the emitter.

 

Circuit Diagram



 

Building the NOT Gate

Step 1: Connect the Power Supply

  1. Connect the positive terminal of the power supply (+5V) to the positive rail of the breadboard.
  2. Connect the negative terminal (GND) to the negative rail.

 

Step 2: Place the Components on breadboard (As per your design)

  1. Place one NPN transistor (Q1).
  2. Place one switch (S1).
  3. Place one Red LED.

 

Step 3: Connect the Resistors (Use jumping wires for connections if required)

  1.  Connect resistor (R1) between the positive rail (+5V) and the input of S1.
  2.  Connect the output of S1 to the base of Q1.
  3. Connect the Collectors of Q1 to the one end of resistor R2
  4. Connect another end of R2 to the positive rail.
  5. Connect Emitter of Q1 the ground rail (GND).

 

Step 4: Connect the LED (To show the OUTPUT visually)

  1. Connect the anode of the LED (L1) to the one end of resistor R3.
  2. Connect another end of resistor R3 to the Collector of Q1.
  3. Connect the cathode of the LED (L1) to the GND.

 

Step 5: Testing the Circuit

  1. Apply different combinations of input voltage.
  2. Don’t press S1, LED should be ON.


 

  1. Press S1, LED should be OFF.


 

Note: Value of resistors can be adjusted as per the requirements.

 

 

I hope you liked the information.

 

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