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2n3904 pins- Pinout, Features, and Applications of 2N3904 Bipolar Transistor

The 2n3904 ranks among the popular transistors that you’ll find in electronic components. It is prevalent in many hobbyist projects for electronic functions like amplification and switching. Join us as we elaborate on 2n3904 pins, electronic applications, and other details of the 2N3906 transistor. 

What are 2n3904 pins?

A Transistor

Fig 1: A Transistor

2N3906 transistors have three pains whose functions are as follows: 

  1. Pin 1 is the emitter pin via which emitter voltage/ current leaves the transistor. 
  2. Also, we have Pin 2, which operates as the existing base pin. It’s imperative in biasing control of the transistor.
  3. Finally, It has a collector pin / Pin 3 via which electric current drains out of the transistor. 

Features of 2N3904

3D Rendering of TO-92 package on white surface

Fig 2: 3D Rendering of TO-92 package on white surface

  1. First, it is an NPN bipolar junction transistor in a TO-92 package type
  2. Also, it features a DC Current Gain (hFE) of 40 to 300 and a 200mA maximum collector current. 
  3. Thirdly, it has a 40V Collector-Emitter Voltage and a 6V maximum emitter-Base Voltage. 
  4. Furthermore, with a 625 milliwatt maximum collector dissipation and 300 MHz maximum Transition Frequency, the transistor has a 5 dB noise level. 
  5. Lastly, it functions best at an operating and storage temperature of -55 – 150 degrees celsius. 

2n3904 equivalent transistor

The 2N3904 is equivalent to the following transistor driver modules:

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

2N3904-based electronics projects

Power transistors on the black surface

Fig 3: Power transistors on the black surface

The 2N3904 is useful in an extensive range of applications. But primarily, you can use it either as each of the following: 

2n3904 pins-As a switch

When operating as a switching, the transistor will function in the Saturation and Cut-Off Region. Thus, in forwarding transistor bias, the transistor is an open switch, while in reverse discrimination, it’s a closed switch. 

The maximum biasing current for these functions is 5mA, and supplying a higher current than this will destroy the power transistors. Therefore, connecting a resistor in series with the transistor’s base pin is imperative. 

The following formula is handy in deducing the correct resistor value that you should use: 

RB= VBE ÷ IB, whereby RB is the resistor value, VBE is the base pin voltage (5V), and IB is the emitter current. 

2n3904 pins-As Amplifier

The transistor will operate as an Amplifier when it functions in the active region. As an amplifier, it can be a power amplifier, voltage amplifier, or current amplifier. Besides, three main amplifier circuit configurations are as follows: 

  • Common collector amplifier
  • Common emitter amplifier
  • Common base amplifier.

The standard emitter amp is the most common of the three listed above. Lastly, the formula below indicates calculating the transistor’s DC gain when it functions as an amplifier.  

Current Gain = Collector Current ÷ Base Current. 


An audio amplifier/ Mixer. 

Fig 4: An audio amplifier/ Mixer. 

The module is helpful in the following applications. 

  1. It’s essential in amplifier modules such as  Audio Preamplifiers and the audio Amplifier Stages.
  2.  Also valuable for sensor circuits, Darlington Pairs, and Driver Modules such as LED driver and Relay Driver. 
  3. Again, it is paramount in TV and other common electronic appliances. 


Above is extensive coverage of the pinout, principle of operation, and applications of the 2N3904 Bipolar Transistor. We welcome any suggestions and queries on the component via our contact channels

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Emma Lu
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