2N3904 NPN Transistor : Pin Configuration & Its Applications

In the mid-1960, both the 2N3906 PNP and 2N3904 NPN transistor were registered by Motorola Semiconductor. These transistors are available in the plastic TO-92 package. This transistor is widely available at a low cost & robust so that beginners and researchers can be used mostly.

Once we look at the flat side of this transistor, three leads are pointed downward. So the three wires can be connecting to these leads from the left side to the right. So that it was marked as EBC (emitter, base & collector) by some manufacturers. This article discusses an overview of a 2N3904 NPN transistor and its working.

What is a 2N3904 NPN Transistor?

2N3904 is a three-terminal NPN BJT (Bipolar Junction Transistor), made with silicon material and enclosed within the TO-92 package. In this type of transistor, the majority of charge carriers are electrons so they carry negative charges always. The state of this transistor can be changed based on the small voltage at the base terminal like 0.7V from reverse bias to forward bias to conduct.

2N3904 NPN Transistor
2N3904 NPN Transistor

The 2N3904 is a common NPN BJT used in the applications of general-purpose switching or low-power amplifying applications. This type of NPN transistor is mainly designed for medium voltage, low power applications and it operates at moderately high speeds.

This 2N3904 NPN transistor is very popular, so it can be used like an amplifier and simple electronic switch so it can handle 200 mA of power & 100 MHz frequency when used it is used as an amplifier.

Pin Configuration

The pin configuration of a 2N3904 NPN transistor is shown below. This transistor includes three terminals which are discussed below.

2N3904 Transistor Pin Configuration
2N3904 Transistor Pin Configuration
  • Pin1 (Emitter): The flow of current will Drain out throughout this terminal.
  • Pin2 (Base): This pin controls the transistor biasing.
  • Pin3 (Collector): Current supplies throughout this terminal

Features & Specifications

The features and specifications of the 2N3904 NPN transistor include the following.


This transistor is available in To-92 Package

  • It is an NPN BJT
  • DC Current Gain or hFE (Max) is 300
  • Voltage from collector to the emitter (VCE) is 40V
  • Continuous Collector current or IC is 200mA
  • Voltage from the base terminal to the emitter (VBE) is 6V
  • Voltage from collector to the emitter (VCE) is 40V
  • Voltage from collector to base (VCB) is 60V

Equivalent 2N3904 NPN transistors are BC636, BC549, BC639, 2N2222 TO-18, 2N2222 TO-92, 2N2369, 2N3906, 2N3055, 2SC5200, etc.

In the 2N3904 NPN transistor, both the emitter and collector terminals will be reverse biased or left open once the base pin is connected at the GND terminal. Similarly, it will be forward-biased once a signal is given to the base pin.

The high gain value of this transistor is 300 which decides the transistor’s amplification capacity. The maximum current supply throughout the collector terminal is 200mA, so the loads which consume above 200mA cannot be connected with the help of this transistor. Once the current supply is given to the base terminal then the transistor can be biased. This IB current must be restricted to 5mA.

Once this 2N3904 NPN transistor is completely biased then it allows a maximum of 200mA to flow across the two terminals like emitter & collector. So this phase is known as saturation region & the typical voltage allowed across the two terminals like collector-emitter/collector base could be 40V & 60V correspondingly.

Once the base current is detached then the transistor will be turned off, so this phase is known as the cut-off region & the VBE could be approximately 600 mV.

LED Flasher Circuit with 2N3904 NPN Transistor

LED flasher circuit using 2N3904 transistor is shown below. This circuit can be built with basic components like breadboard-, connecting wires, battery-9V, capacitor, LED 5mm, LED flasher, resistors like 1k, 10k & 4.7K.

This simple LED flasher circuit is a very simple circuit and easy to design that offers a visual cue in flashing LED form. This circuit mainly uses the basic components which are mentioned above. This is an NPN transistor thus both the terminals like the emitter & the collector are reverse biased once the base pin of this transistor is connected to GND, Similarly, once a signal is given to the base pin of this transistor, then it is connected in forwarding bias.

LED Flasher with 2N3904 Transistor
LED Flasher with 2N3904 Transistor

This LED flasher circuit uses a single transistor to flash a bright LED. The transistor used in this circuit works like a driver that uses a flash rate from a self-flashing LED. So this flash rate can be adjusted by changing the 1KΩ resistor value within the above circuit.

The circuit is designed with a 2N3904 transistor although we can design this circuit by using an NPN transistor. For this circuit, a 6V DC battery otherwise power supply is used to provide power supply to the circuit. This simple LED flashing circuit is used in different devices like doorbells, toys for generating siren sounds, or flashing lights.

The main difference between 2N3904 & 2N3906 is the type of transistor. Here, 2N3904 transistor is NPN type whereas 2N3906 is PNP type. In the 2N3904 transistor, the collector to base voltage or VCB is 40V whereas, in the 2N3906 transistor, the VCB is 60V.

Where to Use/Applications

The applications of the 2N3904 NPN transistor include the following.

  • This transistor is used in driver modules like an LED driver, relay driver, etc.
  • Used in amplifier modules like a signal amplifier, audio amplifier, etc.
  • Both the voltages like VBE & VCB are high so they can be used for controlling voltage loads up to 40V.
  • Usually, it is used in TVs & other home appliances
  • When it works as a switch then controls heavy loads due to high gain and less saturation voltage.
  • This transistor can also be used in fast switching applications like PWM (pulse width modulation) due to its quick switching speed.
  • It is used in sound amplifiers because it includes high current gain, so used as an amplifier.

Thus, this is all about an overview of the 2N3904 NPN transistor datasheet. Generally, this transistor is made with Si material and used as an amplifier and switch. Once this transistor works like a switch then it supports 100mA of current. Similarly, it supports 100MHz when it works as an amplifier. A similar 2N3904 NPN transistor is 2N2222A. This transistor is available in the TO-92 package & used in different applications like TV, switch, amplifier, etc.

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