2N3904 NPN Transistor: Equivalents, Manufacturer, Working Principle and Applications

Ⅰ. Overview of 2N3904 transistor

Ⅱ. Manufacturer of 2N3904 transistor

Ⅲ. Symbol, footprint and pin configuration of 2N3904 transistor

Ⅳ. What are the features of 2N3904 transistor?

Ⅴ. Technical parameters of 2N3904 transistor

Ⅵ. How does the 2N3904 transistor work?

Ⅶ. Maximum ratings of 2N3904 transistor

Ⅷ. What are the applications of 2N3904 transistor?

Ⅸ. How to use 2N3904 transistor?

The 2N3904 is a commonly used transistor that is widely used in electronic circuits for a variety of applications. To make better use of it, in this article, we will explore the physical structure of the 2N3904 transistor, learn about its replacement models, features, technical parameters and pin configuration, as well as its working principle and applications.

The 2N3904 is a discrete semiconductor transistor suitable for general-purpose low-power amplification or switching applications. It is made of silicon material and comes in TO-92 package. Most of the charge carriers in such transistors are electrons, so they always have a negative charge. Its state can change from reverse bias to forward bias according to a small voltage (such as 0.7V) at the base terminal to conduct.

This component is tailored for low current, low power, and medium voltage applications, offering reliable performance at moderate speeds. It serves as a complement to the 2N3906 transistor, with both models having been introduced by Motorola Semiconductor in the mid-1960s. It can fulfill the roles of both an amplifier and a switch, capable of managing up to 100mA of current when used as a switch and achieving a maximum bandwidth of 100MHz when used as an amplifier.

Replacements and equivalents:

• BC549

• BC639

• S8050

• 2N2222

• 2N3904RLRAG

• 2N3904RL1G

• 2N4401

• 2N3055

The 2N3904 transistor is manufactured by Diotec Semiconductor. The company was founded in 1973 and is headquartered in Germany with a branch in Shanghai. The company has more than forty years of experience in diode R&D and manufacturing and is committed to providing customers with professional, high-quality diode and rectifier products. Diotec's main products include TVS tubes, triodes, ultra-fast recovery diodes, Zener tubes, fast recovery diodes, Schottky diodes, ordinary rectifier diodes and rectifier bridges, etc.

The following figure shows the symbol, footprint and pin configuration of the 2N3904 transistor respectively.

Pin 1 (Emitter): Current drains out through emitter

Pin 2 (Base): Controls the biasing of transistor

Pin 3 (Collector): Current flows in through collector

• Low noise: It is suitable for applications with higher noise requirements, such as radios, audio amplifiers, etc.

• Good voltage gain: This type of transistor has excellent gain. When the collector is connected to the base, the base current increases significantly. But when the collector is connected to the ground terminal, the base current is significantly reduced.

• Low saturation voltage: The saturation voltage of 2N3904 is usually lower than 0.2V. This feature allows it to exhibit lower energy consumption in switching circuits.

• High current amplification: Its current amplification is usually between 100 and 300, which can amplify the input signal to a larger output signal.

The 2N3904 transistor is composed of three levels of semiconductor materials, namely the emitter area, the base area and the collector area. The emitter region is an N-type semiconductor, the base region is a P-type semiconductor, and the collector region is an N-type semiconductor. In the absence of any external voltage, the 2N3904 is in a closed state, and the PN junction between the emitter region and the base region is forward biased, preventing current from flowing. However, when an appropriate voltage is applied to the base, this voltage will cause the forward bias voltage of the PN junction in the base region to reach the destruction voltage, causing the PN junction to become conductive. At this time, electrons in the base region will be injected into the emitter region, forming a current flow. At the same time, the PN junction in the collector area remains reverse biased, which helps prevent current from flowing through it.

Limit parameters are key elements that describe the approximate usage conditions of a product. When designing products, we usually set normal operating conditions and try to stay away from these extreme parameters, because even approaching these parameters may reduce the device life. We must ensure that transistors are used within specified limits to prevent overheating or damage.

• Pulse generator: It is a common transistor that can be used to generate pulse signals. In timers and frequency generators, it is often used in conjunction with other components to generate various required pulse waveforms.

• Switch: 2N3904 can also be used as a switch to control large current or high voltage loads. In digital circuits, it can be used in the construction of logic gates, as well as switch control circuits.

• Voltage regulator circuits: 2N3904 can be used in voltage regulator circuits to regulate the voltage output of a power supply. It can also be used in switching regulator circuits to convert voltage levels efficiently.

• Amplifier: It can be used to design various types of amplification circuits, including common-emitter amplifiers, common-collector amplifiers and common-base amplifiers, to amplify weak signals generated by sensors for subsequent processing or measurement.

• Collector follower: 2N3904 can be used as a collector follower through which low output impedance can be achieved to enable driving loads such as motors or other high current devices.

First, we select appropriate transistor parameters based on actual application requirements, such as current amplification, saturation voltage, maximum collector current, and maximum collector-emitter voltage. In the circuit design, we place the 2N3904 transistor in the appropriate position and rationally layout other components to optimize the signal transmission path and reduce signal loss and interference.

The bias circuit is one of the prerequisites for the operation of the transistor. A well-designed bias circuit can improve the performance and efficiency of the transistor. We can optimize the bias circuit by adjusting the size of the bias resistor and using a constant current source.

Next, we connect the input signal to the base pin of the 2N3904 transistor and ensure that the input signal's amplitude and frequency range meet the transistor's specifications.

We then connect the collector pin of the 2N3904 transistor to the load that outputs the signal, making sure that the impedance of the load matches the output impedance of the transistor.

Again, we provide a suitable DC power supply for the 2N3904 transistor to ensure that its operating voltage and current meet the specifications.

After completing the circuit design and connections, we perform testing and debugging to ensure that the 2N3904 transistor can work properly in the circuit and achieve the expected performance indicators.

Frequently Asked Questions

1. What is the function of 2N3904?

The 2N3904 is an extremely popular NPN transistor that is used as a simple electronic switch or amplifier that can handle 200 mA (absolute maximum) and frequencies as high as 100 MHz when used as an amplifier.

2. Is 2N3904 a silicon?

The CENTRAL SEMICONDUCTOR 2N3903 and 2N3904 types are NPN silicon transistors designed for general purpose amplifier and switching applications.

3. What is the gain stage of 2N3904?

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.

4. What is the amplification factor of 2N3904?

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.

5. What is 2N3904 NPN transistor TO-92?

The 2N3904 transistor is a silicon epitaxial planar NPN general purpose amplifier and switch. The useful dynamic range extends to 100 mA as a switch and to 100 MHz as an amplifier.