2N3904 Transistor Pinout, Datasheet, Equivalent

The 2N3904 transistor is a versatile and widely used component in electronic circuits for switching and amplification.  The maximum output current across collector to emitter is 200mA , means we can not connect load that required current more than of 200ma. The 2N3904 is a widely used NPN bipolar junction transistor (BJT) suitable for general-purpose low-power applications. The PNP complementary pair of this transistor is 2N3906.

The 2N3904 transistor typically comes in a TO-92 package with three pins

Equivalent or alternative of 2N3904

BC548, BC549, BC546(Pin CBE), 2N2222 (Pin EBC)

Pin Configuration

1. Collector (C)
2. Base (B)
3. Emitter (E)

Material of Transistor: Si

Polarity: NPN

• Maximum Collector-Base Voltage (V_cb): 60 V
• Maximum Collector-Emitter Voltage (V_ce): 40 V
• Maximum Emitter-Base Voltage (V_eb): 6 V
• Maximum Collector Current I_{c max}: 200m A
• Max. Operating Junction Temperature (T_j): 135 °C
• Transition Frequency (ft): 300 MHz
• Collector Capacitance (Cc): 4 pF
• Forward Current Transfer Ratio (hFE), Max : approx 200 
• Package: TO-92

Uses of 2N3904

1. Switching Applications: The 2N3904 can be used to switch low-power devices on and off- In a switching circuit:
   • The emitter is connected to ground.
   • The collector is connected to the load (e.g., an LED) and then to the positive voltage supply.
   • A resistor is placed between the base and a control signal to limit the base current.

   When a positive voltage is applied to the base, it forward-biases the base-emitter junction, turning on the transistor and allowing current to flow through the load.

2. Amplification: It can amplify low-power audio or other signals in electronic circuits- In an amplifier circuit:
   • The emitter is connected to ground through a resistor.
   • The base is connected to the input signal through a coupling capacitor.
   • The collector is connected to the positive voltage supply through a load resistor.
3. Analog Circuits: Used in oscillators, signal generators, and voltage regulators.
4. Complementary Pair: Often used with its PNP counterpart, the 2N3906, in push-pull amplifier configurations.

Working Principle of 2N3904 transistor

The 2N3904, being an NPN transistor, operates by controlling the current flow through its collector-emitter path with the current applied to its base-emitter junction. Here’s a breakdown of its operation in different modes:

Cutoff Mode

• Condition: No base current (IB) flows.
• Effect: The transistor is off, and no current flows from the collector to the emitter (IC = 0).

Active Mode

• Condition: The base-emitter junction is forward-biased (Vbe ≈ 0.7V), and the base-collector junction is reverse-biased.
• Effect: A small base current controls a larger collector current. The transistor can amplify the input signal.

Saturation Mode

• Condition: Both the base-emitter and base-collector junctions are forward-biased.
• Effect: The transistor is fully on, and maximum current flows from the collector to the emitter. This mode is typically used for switching.

Biasing

For an NPN transistor like the 2N3904

• The emitter is connected to ground.
• The base must be at a higher voltage than the emitter for the transistor to turn on.
• The collector is connected to a positive voltage supply through a load.

In a switching circuit:

• The emitter is connected to ground.
• The collector is connected to the load (e.g., an LED) and then to the positive voltage supply.
• A resistor is placed between the base and a control signal to limit the base current.

When a positive voltage is applied to the base, it forward-biases the base-emitter junction, turning on the transistor and allowing current to flow through the load.

In an amplifier circuit:

• The emitter is connected to ground through a resistor.
• The base is connected to the input signal through a coupling capacitor.
• The collector is connected to the positive voltage supply through a load resistor.

The input signal at the base modulates the current flow from the collector to the emitter, resulting in an amplified output signal.

2n3904 datasheet (809kb)