Simple NAND Gate Circuit using Transistors

An essential component of digital logic circuits is the NAND gate.

It operates in the opposite way from an AND gate, only producing a HIGH output when any of its inputs are LOW.

It is interesting to note that NAND gates are considered to be a ‘universal gate’ since they may be used to construct any other digital logic function, including AND gate, OR gate, NOT gate and so on.

Circuit Working:

Parts List:

Powering the First Transistor Q1:

First, we attach the positive power supply Vcc to Q1s collector or drain point.

To regulate the current going into Q1, a resistor R5 is connected in series with both of them.

This determines the transistors power supply.

Linking the Transistors:

Afterwards, we attach the emitter (or output point) of Q1 straight to the second transistors Q2 collector.

In order for the NAND gate to function this establishes a connection between the two transistors.

Taking the Output:

Q1s collector has an additional function.

It is attached to the output terminal (output LED1) , which is where the NAND gates final signal will come from.

Handling the Inputs:

The input signals are our current area of concern.

The base control point of Q1 and the first input terminal (push button1) are connected by a resistor R1.

To ensure correct operation, this resistor restricts the amount of current that enters the base.

Using a resistor R2 between the base of the second transistor Q2 and the other input terminal (push button2), we repeat this process for the second transistor.

Why It Operates in a Different Way Than an AND Gate

There is a significant distinction between an AND and NAND gate despite their similar designs.

The emitter of the second transistor is normally linked to the AND gates output.

However, the output of our NAND gate comes from the first transistors Q1 collector.

This minor adjustment completely changes the reasoning.

Comprehending the Behavior of the Output:

Assume that both inputs of (push button1 and push button2) are getting high voltage and are HIGH.

In this case, both Q1 and Q2 transistors would be operational enabling unrestricted current flow from Vcc via their respective collector emitter routes to ground.

By doing this, the current is effectively diverted away from the output terminal (output LED1) and created as a bypass.

As a result, there is a drop in the output voltage and a LOW output signal.

Conversely, the matching transistor Q1 or Q2 will be switched off if either input of (push button1 and push button2) is LOW (receiving low voltage).

The electricity takes a different route through the output circuit (often shown by an LED) as it cannot pass through the blocked transistor to ground.

The output voltage increases as a result of this current flow producing a HIGH output signal.

To summarize, a NAND gate performs the NAND logic function by only producing a HIGH output when any one of its inputs is LOW.

Formulas:

Here are some fundamental formulas and factors to take into account while creating a transistor-based NAND gate circuit:

Base of Transistor resistor

To guarantee appropriate saturation, determine the base resistor Rbase for the 2N2222 transistor:

R_{base ​}= V_in​ − V_be​​ / I_b​

where,

• The input voltage, Vin is usually 9V.
• The transistors base-emitter voltage, or Vbe is around 0.7V for 2N2222.
• The basic current needed to reach saturation is Ib.

LED Current Limiting Resistor:

To restrict the current, figure out the resistor RLED for each LED.

R_LED​ = ​V_supply​ − V_LED​​ / I_LED

where,

• The supply voltage is denoted by Vsupply 9V.
• The forward voltage drop of an LED is represented by VLED, which is usually around 2V for ordinary LEDs.
• The intended LED current, or ILED, is generally 20mA for ordinary LEDs.

Push button pull up resistors:

In order to maintain a predetermined logic level even when the push buttons are not touched, use pull-up resistors.

R_{pull − up​} = V_supply​​ / I_{pull − up​}

where,

• When the push button is open, the current required to pull the input high is called Ipull-up.

You may use 2N2222 transistors, resistors, LEDs and push buttons to create a working NAND gate circuit by utilizing these calculations and instructions.

Adapt component combinations and values to your circuits individual needs and desired performance characteristics.

How to Build:

To build a Simple NAND Gate Circuit using Transistors follow the below mentioned steps for connections:

• Assemble all the components as mentioned in the diagram above
• Connect collector of transistor Q1 to positive supply through resistor R5, connect base of transistor Q1 to push button1 through resistor R1, connect emitter of transistor Q1 to collector of transistor Q2
• Connect output LED1 anode between collector of transistor Q1 and resistor R5 and cathode of output LED1 to ground.
• Connect collector of transistor Q2 to emitter of transistor Q1, connect base of transistor Q2 to push button2 through resistor R2, connect emitter of transistor Q2 to ground.
• Connect resistor R3 and input LED1 between push button1 and resistor R1.
• Connect resistor R4 and Input LED2 between push button2 and resistor R2.

Additional Information:

• The kind of transistor and voltage of the power source might affect the particular resistor values.
• This is only a basic illustration there are design modifications depending on use.
• When working on electronics projects, use caution and adhere to safety precautions when handling electronic components.

Conclusion:

The Simple NAND Gate Circuit has a strong and flexible functionality despite its relatively basic transistor based architecture.

It is an essential component of digital logic circuits due to its capacity to carry out the NAND operation which produces an output that is HIGH only when all inputs are LOW.

References:

NAND gate

Multiple NAND gates built with transistors linked together