BC547 Transistor: Basic Knowledge, Pin Configuration & Features

What is BC547 Transistor


Do you want to Discover the Power of BC547? If the answer is yes! then this blog post is for you to learn about the BC547 transistor, its role as a switch, its working state, key features, equivalent transistors, and a wide range of applications in electronics. Whether you're a beginner or a seasoned pro, this comprehensive guide is a must-read for anyone looking to enhance their knowledge of the BC547 transistor. Get ready to unlock the full potential of this versatile and reliable component!

What is BC547 Transistor?

A transistor essentially acts as a switch that is operated by electricity. The emitter, collector, and base are three lines: an input, an output, and a Base. Like a switch, the control line (base) will connect the emitter and collector when it is activated. Transistors are frequently employed as amplifiers because the power between the emitter and collector can be higher than the base. 


BC547 Transistor


Specifically, it is a BC547 NPN Bipolar Junction Transistor (BJT). An amplifier of current, a transistor is nothing more than the transfer of resistance. This transistor's base terminal, which has a little current, controls the emitter and base terminals' higher current. This transistor's primary tasks are switching and amplification. An NPN transistor's base is shown by a short vertical line, and the emitter, is shown by a diagonal line connecting the base and it is represented by an arrowhead pointing away from the base. 


The gain value of the BC547 transistor, which ranges from 110 to 800, affects the transistor's capacity for amplification. We cannot use this transistor to connect loads that use more than 100mA since the maximum amount of current that can pass via the Collector pin is 100mA. To bias a transistor, current must be supplied to the base pin; this current (IB) should be kept to a maximum of 5mA. 


The transistor has a +Ve voltage at its base and a -Ve voltage at its emitter. The transistor's base terminal is always positive to the emitter, and the collector voltage supply is always positive concerning the emitter terminal. Through the RL, the collector terminal is connected to the VCC. The highest base current is constrained by this resistor's restriction of current flow. The transistor action of an NPN bipolar transistor is represented by the flow of electrons using the base. The connection between the input and output circuits is the primary property of this transistor action. Because the control that the base exercises over the collector to emitter current results in the transistor's amplifying capabilities. When the transistor is turned ON, the IC supplies a significant amount of current between its collector and emitter terminals. However, this only happens when a very small biassing current, designated Ib, passes through the transistor's base terminal.  


As previously mentioned, a transistor is operated in the Saturation and Cut-Off Region then it acts as a switch. A transistor will operate as an Open switch during forwarding Bias and as a Closed switch during Reverse Bias. This biassing is accomplished by applying the necessary current to the base pin. The maximum biassing current should be 5mA, as was previously stated. A resistor is always added in series with the base pin since a transistor will be destroyed by currents greater than 5 mA. Using the formulas below, the value of this resistor (RB) can be determined.


RB  = VBE / IB


Fig. 2. Operation of the transistor in different modes

When the transistor acts as an Amplifier:

In an active region, a transistor works as an amplifier. It has several settings where it can enhance power, voltage, and current.


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

The active portion of the curve between V0 and Vi is where a transistor operates as an amplifier, as we saw earlier. The pace at which the signal output varies in relation to the signal input is shown by the slope of the linear portion of this curve. We can infer that the rate is negative since the output of the CE amplifier falls as the input voltage rises because the output is not just ICRC but also VCC. The output and the input signal are out of phase in this case. Now, if we express the tiny variations in the input and output voltages as Vo and Vi, respectively,

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

BC547 Pin Diagram


BC547 Pin Diagram


Collector - Current flows through this pin, The majority of charge carriers released by the Emitter are collected in the Collector region. The quantity of current that passes via the Emitter to the Collector is triggered and controlled by the Base region.


Base - Control the biasing of transistor

Emitter - Current drains out through this pin, the Emitter region provides charge carriers to the Collector via Base


The working state of the transistor includes:

  1. Forward biased 
  2. Reversed biased


  • When current flows from collector to emitter,¬†
  • The transistor will begin working as a closed switch if a HIGH signal (often 5V) is applied to the base terminal, this is referred to as forward biassing.
  • The load must be less than the BC547's 110mA maximum collector current limit.


  • The transistor is considered to be working as Reverse Biased if the Base Terminal is connected to Ground (0V), in which case the Collector and Emitter will function as an open switch.
  • No current will flow through the transistor in a¬†reverse-biased state.


Below is a picture of an ON/OFF circuit switch that uses the transistor BC547. Once the circuit receives a power supply, the circuit is activated. The relay enters an off mode after the circuit receives the supply. In order to preserve the cut-off condition, the base terminal of the Q3 transistor is thus held high throughout the R7 resistor.


The Q4 transistor will begin to conduct when the S2 switch is turned on, allowing the relay "L3" to latch. When power is turned on, the Q3 transistor's base terminal will be dragged downward, and the L2 LED will begin to blink. The voltage at the collector terminal of the transistor Q3 using the R8 resistor turns on the Q4 transistor. In addition, the relay L3 will be turned off because the pull-down base of transistor Q4 throughout the R8 resistor causes the base terminal of transistor Q3 to be pulled up.


Features of BC547

  1. The maximum DC Current Gain (hFE) of a bi-polar NPN transistor is 800.
  2. 100mA is the continuous collector current (IC).
  3. Base Current (IB) at the Emitter is limited to a maximum of 5mA at 6V.
  4. included in the To-92 package
  5. The polarity of the transistor is N-P-N(Negative - Positive - Negative)The semiconductor package with the 300MHz transition frequency is 92.
  6. 625 mW is the power dissipation.

BC547 Equivalent Transistors

Transistors come in many different varieties, and the BC547 is a bipolar junction transistor (BJT). There are transistors with just one junction, like the junction field-effect transistor, and transistors with no junctions at all, like the metal oxide field-effect transistor (MOSFET). The properties can be planned for and attained during transistor design and production. Due to a process of doping, the negative (N)-type material inside an NPN transistor has an excess of electrons while the positive (P)-type material does not.

  • The voltage and current specifications of the 2n3904 are an exact match for those of the BC547 transistor.
  • The 2n3904 has a gain of 300hFE and a transition frequency of 300MHZ.
  • Both transistors have the same applications.¬†
  • The NPN bipolar transistors mentioned are all equivalent to the 2N2222, with most of them being identical.

BC547 Transistor


  • Common applications for BC547 include pulse-width modulation, fast switching, and a current amplifier (PWM).¬†
  • Switching and amplification in general¬†
  • LED, electronic relay, and other device drivers¬†
  • PWM preamplifiers for audio (Pulse Width Modulation)¬†
  • LED blinking circuits¬†



In this blog post, we have learned that BC547 serving as an intermediary between current and circuit, holds the capacity to operate in both saturation and cut-off modes. With its unparalleled features, such as its high gain, low voltage requirements, and remarkable frequency response, the BC547 is the go-to choice for a plethora of applications including amplifiers, oscillators, and switching circuits. For those seeking to build anything from a straightforward switch to a labyrinthine electronic system, the BC547 transistor is a non-negotiable component, providing unflinching and efficacious performance.


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Frequently Asked Questions

1. What is BC547 transistor used for?

The BC547 NPN bipolar junction transistor is top pick for low-power applications, such as illuminating LEDs, amplifying sensor signals, and inciting action in miniscule relays and motors. Its accessibility, affordability, and effortless integration into a plethora of circuit designs have secured its position as a staple in the electronics industry.

2. Is BC547 transistor NPN or PNP?

The BC547 is a bipolar junction transistor (BJT) with an NPN configuration, meaning it has a negatively charged layer between two positively charged layers. This configuration allows it to be used as an amplifier or switch in electronic circuits.

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