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Introduction to 2N3904

Hello everyone! I hope you will be absolutely fine and having fun. Today, I am going to give an Introduction to 2N3904. It is basically an NPN transistor made up of silicon material. It acts as a general purpose amplifier and switch. You should also have a look at Introduction to 2N2222, which is also an NPN transistor and considered as 2N3904 equivalent. It is mostly used for lower power amplifiers and switching applications. Its major functional area is enclosed in TO-92 package. Its a silicon NPN general purpose bipolar junction (BJT) transistor designed for switching purpose as well as for an amplifier. Its can bear lower amount of current, lower power and medium voltage levels. It is most commonly used BJT due to its smaller size, wide availability and low cost. It is less sensitive to fluctuations in voltages and currents as compared to other BJT's.

Where To Buy?
No.	Components	Distributor	Link To Buy
1	2N3904	Amazon	Buy Now

Introduction to 2N3904

• 2N3904 is a silicon NPN Bipolar Junction Transistor (BJT), enclosed in TO-92 package and is normally used for switching & amplification purposes.
• 2N3904 Pinout consists of 3 Pins i.e. Base, Emitter & Collector.
• As it's an NPN transistor, so major charge carriers are electrons caryying negative charge.
• Small voltage at base(around 0.7V) changes its state from reverse to forward biased and starts conducting.
• It has a wide range of applications i.e. used in televisions, home appliances, medium-load switches, PWM applications etc.

Now let's have a look at 2n3904 Pinout:

2N3904 Pinout

• 2N3904 Pinout has three pins in total:
  1. Emitter denoted by E
  2. Base denoted by B.
  3. Collector denoted by C.
• 2N3904 Pin Diagram is shown in below figure:

• 2N3904 Pinouts alongwith their symbols are shown in the table given below.

Let's have a look at the Datasheet of 2N3904:

2N3904 Datasheet

• In order to get in-depth knowledge on any component, must read its datasheet. Here's the link to download 2n3904 Datasheet:

Introduction to 2N3904 Let's have a look at the equivalents of 2N3904 NPN Transistor:

2N3904 Equivalent

Although common transistors such as 2N3904 are easily available in local/online electronics stores, but its wise to know the alternatives. So, 2N3904 equivalents are as follows:

• BC636
• 2N3055
• 2N2222
• BC549
• BC639
• 2SC5200
• 2N2369
• 2N3906

Now let's have a look at poewr ratings of 2N3904:

2N3904 Ratings

• Transistors are available in different ranges of power ratings and their selection depends on circuit's requirements.
• So, a circuit designer's task is to select an optimized transistor for its circuit, which should fullfill all its power equirements & must be cost efficient.
• If current/voltage passing through a transistor exceeds its ratings, the transistor may burnt out.
• Below table shows 2N3904 Ratings:

2N3904 Ratings
No.	Parameter Name	Parameter Value
1	C-E Voltage (VCEO)	40V (DC)
2	C-B Voltage (VCBO)	60V (DC)
3	E-B Voltage (VEBO)	6V  (DC)
4	Collector Current (IC)	200mA

Now, let's have a look at few applications of 2N3904:

2N3904 Applications

2N3904 is one of the most commonly used NPN transistor because of its low-cost, high-speed and small-size. Few of 2N3904 applications are as follows:

• It's normally used as a simple switch to control heavy loads, because of its low saturation voltage and high gain.
• It's used in home appliances i.e. TV, LCDs, stereo systems etc.
• It's also used in fast switching applications i.e. pulse width modulation(pwm), because of its fast switching speed.
• 2N3904 is also in signal amplification projects(i.e. sound amplifiers) as it has high current gain & thus can be used as an amplifier.

2N3904 Transistor as a switch

• In normal state, 2N3904 acts as reverse biased and there's no conduction between Collector & Emitter.
• When small voltage applies at its Base Terminal(normally 5V), 2N3904 converts its state from reverse to forward biased and conventional current starts flowing from Collector to Emitter.

Now, let's design a simulation to practically understand, how 2N3904 transistor acts as a switch?

2N3904 Proteus Simulation

• Let's first control a simple LED on/off state using 2N3904 NPN transistor
• As shown in below figure, power is supplied at Collector and LED is connected at the Emitter with resistor(to limit current) & grounded from the other end.

• As there's no voltage applied at Base Terminal, so 2N3904 is reverse biased and thus LED is OFF.
• Now when we have applied 5V at Base Terminal(using LogicState in Proteus), 2N3904 gets forward biased and now LED is ON, as shown in below figure:

• So, that's how we can use 2N3904 transistor as a switch.

In above simulation, we have controlled a simple LED and have used a manual switch. Now, I am going to control a DC motor with Arduino.

2N3904 Arduino Interfacing in Proteus

• I have made another simulation in Proteus ISIS for DC motor control using 2N3904.
• The screenshot of the simulation is shown in the figure below.

• The complete Arduino source code of the above simulation is given below.
• You have to get the hex file in Arduino to observe the results properly.

int MotorInput = 2;
int MotorOutput = 7;

void setup() 
{
    pinMode(MotorInput, INPUT_PULLUP);
    pinMode(MotorOutput , OUTPUT);
}

void loop() 
{
    if(digitalRead(MotorInput) == HIGH)
    {
      digitalWrite(MotorOutput, HIGH);
    }
    if(digitalRead(MotorInput) == LOW)
    {
      digitalWrite(MotorOutput, LOW);
    }
  
}

• The running form of the above simulation is shown in the below figure:

• From the above figure you can see that after uploading .hex file and running the simulation you need to change the level of logic state from 0 to 1, and the motor will start to rotate.
• You can download the complete Proteus ISIS simulation as well as complete Arduino source code, here by clicking on the button below.
• Just download .rar file, extract it and enjoy the complete package.

Introduction to 2N3904

• You should watch this below video to understand how to run this Proteus Simulation:

So that is all from the tutorial Introduction to 2N3904. I hope you really enjoyed this tutorial. If you face any sort of problem regarding any thing, you can ask me anytime in comments without even feeling any kind of hesitation. I will try my level to entertain you and to solve your issues in a better way, if possible. Our entire team is 24/7 here to entertain you and to solve your issues in a way or the other. I will explore different IC's in my later tutorials and will surely share all them with all of as you as well. So, till then, Take Care :)