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AND Gate Circuit using Transistors

AND gate is a basic digital logic gate.

It gives high output only when both inputs are high.

In this AND Gate Circuit using Transistors is easy to make.

This is a simple example of transistor logic gate.

Truth Table for AND Gate:

Input AInput BOutput Y
0 (LOW)0 (LOW)0 (LOW)
0 (LOW)1 (HIGH)0 (LOW)
1 (HIGH)0 (LOW)0 (LOW)
1 (HIGH)1 (HIGH)1 (HIGH)

Output Y becomes HIGH only when both inputs A and B are HIGH.

If any one input is LOW then output remains LOW.

Symbol of AND Gate:

Circuit Working:

Parts List:

ComponentValue Quantity
Resistors1k1
10k2
SemiconductorsTransistors (NPN) BC5472
Power Supply +5V DC1

The circuit has two inputs A and B.

When both inputs are logic 1 (high) then both transistors Q1 and Q2 conduct.

Then current flows from +5V to ground through both the transistors.

This makes the output Y low (logic 0) at emitter of Q2.

When any input is low then one transistor cuts off and no current flows,

and the output Y stays high (logic 1).

So output Y = A × B (AND gate function).

Formulas with Calculations:

Circuit Formula with Calculation are shown below:

Output logic follows AND rule: Y = A × B.

When A = 1 and B = 1 then

Both Q1 and Q2 ON then current flows with Y = 1.

When A = 0 or B = 0 then

Any transistor is OFF with no current path then Y = 0.

To find base current:

Ib = (Vin – Vbe) / Rb

Assume Vbe = 0.7V and Vin = 5V, Rb = 10kΩ

Ib = (5 – 0.7) / 10000 = 0.00043A = 0.43mA

Collector current:

Ic = β × Ib

Assume β = 100

Ic = 100 × 0.43mA = 43mA

This is enough to drive small loads.

How to Build:

To build a AND Gate Circuit using Transistors following are the connection steps:

Transistor Q1 BC547 connection:

Transistor Q2 BC547 connection:

Conclusion:

AND Gate Circuit using Transistors is simple and easy to build.

It helps to understand digital logic using analog components.

Only when both inputs are high, output becomes high.

Useful for logic control and basic learning of transistor switching.

References:

AND gate

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