BC547 Transistor: Basic Knowledge, Pin Configuration & Features

What is BC547 Transistor


Are you ready to discover the power of BC547?

If the answer is Yes! The purpose of this blog article is to teach you about the BC547 transistor, its duty as a switch, its operating state, essential features, comparable transistors, and a variety of electrical applications.

Whether you're a novice or an experienced professional, this thorough book is a must-read for anybody wishing to improve their understanding of the BC547 transistor. Prepare to realize the full potential of this flexible and dependable 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 BC547 transistor's gain value, which ranges between 110 and 800, determines its amplification capacity.

This transistor cannot be used to connect loads that draw more than 100mA since the Collector pin can only carry 100mA of current. To bias a transistor, current must be given to the base pin; this current (IB) should not exceed 5mA.

The transistor's base voltage is +Ve, while its emitter voltage is -Ve. The transistor's base terminal is always positive in relation to the emitter, as is the collector voltage supply.

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 occurs when a very modest biasing current, Ib, flows through the transistor's base terminal.


As previously stated, when a transistor is in the Saturation and Cut-Off Regions, it functions 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 a single junction, such as the junction field-effect transistor, and transistors with no junctions, such as the metal oxide field-effect transistor (MOSFET).

These properties may be planned for and included during transistor design and manufacture. Doping causes the negative (N)-type material in an NPN transistor to have more electrons than the positive (P)-type material.

  • 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.

The BC547 is an excellent choice for oscillators, switching circuits, and amplifiers, among other applications, thanks to its high gain, low voltage requirements, and amazing frequency responsiveness.

The BC547 transistor is an essential component for anybody developing anything from a basic switch to a large electronic system because it delivers consistent and efficient 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.

3. How do I identify a BC547 transistor?

There are mainly two ways to identify a BC547 transistor. Start by checking the transistor itself for marks. "BC547" and other codes should be printed on it if it's in good condition. If they are hard to see or missing use a multimeter to check.

Set the multimeter to diode mode. Find the transistor's base (B), collector (C), and emitter (E) pins. To check the base-emitter junction, attach the red probe to the base pin and the black probe to the emitter pin. You should see a voltage decrease of around 0.7V. Instead of the base-collector junction, attach the black probe to the collector pin. Again, you should notice a tiny voltage reduction in forward bias. In reverse bias, the resistance reading should be high. This method helps you to determine if the transistor functions correctly even though you can't see the marks well.

4. Can I use BC548 instead of BC547?

Yes, you can use a BC548 transistor instead of a BC547. They are very similar and function well in circuits with up to 28 Vdc voltages. The BC548 is an excellent replacement for the BC547, so if you have one, it will be enough in most cases.

5. Is BC547 a BJT?

Yes, the BC547 is a Bipolar Junction Transistor (BJT). BJTs can be used to amplify or switch electrical signals in circuits. The BC547 is popular because it functions well and is dependable for a variety of applications.

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