2n3904 Pin Assignment Micro

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2N3904 Pin Configuration:

Pin Number

Pin Name




Current Drains out through emitter



Controls the biasing of transistor



Current flows in through collector


  • Bi-Polar NPN Transistor
  • DC Current Gain (hFE) is 300 maximum
  • Continuous Collector current (IC) is 200mA
  • Base- Emitter Voltage (VBE) is 6V
  • Collector-Emitter Voltage (VCE) is 40V
  • Collector-Base Voltage (VCB) is 60V
  • Available in To-92 Package

Note: Complete Technical Details can be found at the 2N3904 datasheet given at the end of this page.

2N3904 Equivalent NPN Transistors:

BC549, BC636, BC639, 2N2222 TO-92, 2N2222 TO-18, 2N2369, 2N3055, 2N3904, 2N3906, 2SC5200

Brief Description on 2N3904:

2N3904 is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. 2N3904 has a gain value of 300; this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 200mA, hence we cannot connect loads that consume more than 200mA using this transistor. To bias a transistor we have to supply current to base pin, this current (IB) should be limited to 5mA.

When this transistor is fully biased then it can allow a maximum of 200mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V­CE) or Collector-Base (VCB) could be 40V and 60V respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 600 mV.

2N3904 as switch:

When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region as explained above. As discussed a transistor will act as an Open switch during Forward Bias and as a closed switch during Reverse Bias, this biasing can be achieved by supplying the required amount of current to the base pin. As mentioned the biasing current should maximum of 5mA. Anything more than 5mA will kill the Transistor; hence a resistor is always added in series with base pin. The value of this resistor (RB) can be calculated using below formulae.

Where, the value of VBE should be 5V for 2N3904 and the Base current (IB depends on the Collector current (IC). The value of IB should not exceed mA.

2N3904 as Amplifier:

A Transistors acts as an Amplifier when operating in Active Region. It can amplify power, voltage and current at different configurations.

Some of the configurations used in amplifier circuits are

  1. Common emitter amplifier
  2. Common collector amplifier
  3. Common base amplifier

Of the above types common emitter type is the popular and mostly used configuration. When uses as an Amplifier the DC current gain of the Transistor can be calculated by using the below formulae

                            DC Current Gain = Collector Current (IC) / Base Current (IB)


  • Driver Modules like Relay Driver, LED driver etc...
  • Amplifier modules like Audio amplifiers, signal Amplifier etc...
  • VCB and VBE is high hence can be used to control voltage loads up to 40V
  • Commonly used in TV and other home appliances

2D model of the component:

If you are designing a PCB or Perf board with this component then the following picture from the 2N3904 transistor Datasheet will be useful to know its package type and dimensions.

      NPN Transistor 2N3904 Pinout

Download Datasheet PDF:
2N3904 Transistor Datasheet

TagsNPN Transistor


The 2N3904 is a common NPNbipolar junction transistor used for general-purpose low-power amplifying or switching applications. The type was registered by Motorola Semiconductor in the mid-1960s, together with the complementary PNP type 2N3906, and represented a significant performance/cost improvement, with the plastic TO-92 case replacing metal cans. It is designed for low current and power, medium voltage, and can operate at moderately high speeds. This transistor is low-cost, widely available and sufficiently robust to be of use by experimenters and electronics hobbyists.[1] When looking at the flat side with the leads pointed downward, the three wires emerging from the bottom are connected to, from left to right, the emitter, the base and the collector.[2] Some manufacturers mark "EBC" on the molded part, but all are required to have those connections for a part which is a "2N3904".[3]

It is a 200 mA, 40 V, 625 mW transistor with a transition frequency of 300 MHz,[4] with a minimal beta, or current gain, of 100 at a collector current of 10 mA. It is used in a variety of analog amplification and switching applications.

The 2N3904 is used very frequently in hobby electronics projects, including home-made ham radios, code-practice oscillators and as an interfacing device for microcontrollers.

Related parts[edit]

Electrically similar devices, such as the MMBT3904, are available in a variety of small through-hole and surface-mount packages, including TO-92, SOT-23, and SOT-223, with package-dependent thermal ratings from 625 milliwatts to 1 watt.

The complementary PNP transistor is 2N3906.

The higher-power 2N2222 is a very similar NPN transistor that can safely switch three times as much current as the 2N3904.[5] Nevertheless, in many applications such as variable-frequency oscillators, where lower currents are used to minimize thermal heating and consequent thermal drift of the fundamental frequency, the greater current capacity of the 2N2222 gives it no advantage. Whereas the 2N2222 is optimized to reach its highest gain at currents of around 150 mA, the 2N3904 is optimized for currents of around 10 mA.

Part numbers[edit]

The 2N3904 (NPN) and 2N3906 (PNP) are complementary transistor pairs.

See also[edit]


Further reading[edit]

  • Malvino, Albert; Bates, David (2007). "Reading Data Sheets". Basic Electronics. Tata McGraw-Hill Education. pp. 139–140. ISBN 0-07-066719-5. Retrieved 2011-04-01. 

External links[edit]

Wikimedia Commons has media related to 2N3904.
A 2N3904 in a TO-92 package on a breadboard (lower left)
A 2N3904 made by Motorola
Pinout of 2N3904 in TO-92 package

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