Different use cases of BC547, 2N3904 and 2N2222

Today, I'm going to give you an overview on the BC547, 2N3904 and 2N2222 transistor. This blog is the continuous blog of the series of Transistors so if you wish to read about any other Transistor then you may click on this Link. In this blog, we will be discussing what is BC547, 2N2222, and 2N3904 transistor their pinout, applications, features, circuit diagram and so on.

A transistor is basically a current controlled device. There is an input, output, and a control line referred to as the emitter, collector, and base.



BC547 Pinout


The BC547 is a common NPN (Negative-Positive-Negative) transistor. It is a Bipolar Junction transistor that is commonly used to satisfy the need of quick switching.  These types of bipolar transistors are made up of materials such as germanium, silicon, and gallium arsenide. Transistors contain three semiconductor layers arranged in two different ways: NPN and PNP. The emitter (E), collector (C), and base (B) are the three terminals (B).

Transistor npn

This transistor is commonly used for amplification of current as well as switching purposes. The gain value of the BC547 transistor ranges from 110 to 800, and this value determines the transistor's amplification capacity.  The maximum current that can flow through the Collector pin is 100mA, we can't use this transistor to connect loads that use more than 100mA. We must supply current to the base pin of a transistor to operate it, and this current (IB) should be limited to 5mA.



  • General switching and amplification purposes
  • Driver modules for LED, electronic relay
  • Darlington pair circuits
  • Arduino, robot electronics projects
  • Audio preamplifiers
  • PWM (Pulse Width Modulation)
  • LED flashers circuits
  • Heat sensor circuits


LED Controlling Circuit

When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region.  When we supply current to the transistor's base, it makes a path for the collector current to flow from the base to the emitter.

During Forward Bias, the transistor will act as an Open switch, and during Reverse Bias, it will act as a Closed switch. This biasing can be done by providing the required amount of current to the base pin. The biasing current should be not more than 5 mA. Any current more than 5mA will damage the transistor, hence a resistor is always connected in series with the base pin. The following formulae can be used to calculate the value of this resistor (Rb).

Rb = Vbe / Ib


The voltage does not apply to the base terminal when the switch is in the open condition. The transistor is now in Reverse Bias mode, which means that no current flows through the collector or emitter. The LED is turned off in this situation.

The transistor will not work if a signal (voltage/current) is applied across the collector and emitter but not across the base. However, a small signal across the base is enough to make it work.


BC547 Transistor as an Amplifier

BC547 transistor as an amplifier

When in the Active Region, a transistor operates as an amplifier. It has the ability to amplify power, voltage, and current. The most popular and commonly used configuration is the common emitter type. The DC current gain of the Transistor can be calculated using the formula

DC Current Gain = Collector Current (Ic) / Base Current (Ib)


The input is always applied at the forward-biased junction in the amplification transistor circuit. Similarly, the output can be collected across the reverse-biased junction of the transistor. The input signal is applied to the base-emitter junction, and the output signal is sent through the load to the emitter-collector junction.



2N3904 Transistor pin out


2N3904 is a commonly used general-purpose transistor. It's a bipolar junction transistor (BJT) made up of silicon NPN. It can be used for switching and amplification in a wide range of electronic applications.  The transistor's maximum collector current is 200 mA, allowing users to drive loads under 200 mA in their electronic applications. The 2N3904 also works well as an amplifier, with a total device dissipation of 625 mW,  due to which it can also be used for audio and RF signal amplification purposes. It can bear lower current, lower power, and medium voltages. When compared to other BJTs, it is less sensitive to voltage and current variations.

The 2N3904 is an NPN transistor, when the base pin is held at ground, the collector and emitter are left open (reverse biased), and when a signal is applied to the base pin, the collector and emitter are closed (forward biased). The gain value of the 2N3904 is 300, which determines the transistor's amplification capacity.



  • 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


Intensity Controller Switch

2N3904 transistor as a switch



2N2222 pin out2N2222 is the most commonly used NPN bipolar junction transistor. It can be used for switching applications and amplification of analog signals. The 2N2222 is enclosed in a TO-18 package.

2N2222 transistor is made of either silicon or germanium that has been saturated with either a positively or negatively charged material in a process called doping. A positively charged portion is placed between two negatively charged portions. Because the materials are arranged in the order negative, positive, negative, the device is known as an NPN transistor.

When compared to other similar small transistors, one of its unique advantages is its capacity to handle high currents. It can normally switch an 800mA load current, which is a really high rating when compared to other similar transistors. While performing amplification applications, it receives an analog signal via collectors, and another signal is applied at its base. An Analog signal could be the voice signal having an analog frequency of almost 4kHz (human voice).

 NPN transistor construction



NPN transistors, such as the 2N2222, are commonly employed in VHF (very high frequency) amplifiers and switching applications. The transistor is made up of silicon material. This type of transistor is considered a normal transistor and is used in the same way as an NPN transistor. Base, Emitter, and Collector are the three terminals on this transistor.


The 2N2222 transistor provides a constant DC collector current of 800mA, making it ideal for applications requiring low to medium current. It uses a 10ns delay time, 225ms storage time, 60ms fall time, and 25ms rise time to operate on a high transition frequency of 250MHz. It comes with the TO-92 bundle.



2N2222 Applications

  • Audio Preamplifiers
  • As compared to the normal NPN BC547 transistor, the 2N2222 is extremely similar, but 2N2222 allows 800mA of collector current & also 652mW of power dissipation which can be utilized for driving larger loads as compared toBC547.
  • It is used for PWM due to its quick response
  • It is typically used in automation & embedded projects.
  • Darlington Pairs
  • Audio Amplifier Stages
  • Switching many loads at the same time 
  • RF Circuits
  • Sensor Circuits
  • It is mostly used in embedded and automation projects.


2N2222 as a Switch 



Pin Name Description
Emitter Current flows out through emitter
Base Controls the biasing of the Transistor
Collector Current flows in through collector



TRANSISTOR BC547 2N3904 2N2222
Package TO-92 TO-92 TO-18
Collector base Voltage 50V 60V 60V
Collector emitter Voltage 45V 40V 30V
Emitter base Voltage 6V 6V 5V
DC Current gain 800 300 75
Base current 200mA 50mA 200mA
Collector current 100mA 200mA 800mA
Transition frequency 300MHz 300MHz 250MHz
Collector Capacitance 6pF 4pF 8pF
Emitter capacitance  9pF 8pF 25pF
Total power dissipation 500mW 625mW 500mW
Noise  10dB 5dB 4dB
Max. Junction temperature 150 degree C 150 degree C 150 degree C



If you wish to buy any of these transistor then you may click on their names present down.





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