Generally, BJTs are significant electronic components that work as basic building blocks within modern electronic circuits. These transistors are categorized into PNP and NPN transistors. In ICs or discrete components, thousands to millions of transistors are incorporated. It is essential to note that the electron movement is much faster & better as compared to the hole movement, so this is the reason to use an NPN transistor over a PNP transistor in many applications. These transistors are made with Silicon material. This article provides brief information on one of the NPN transistors namely; the BC550 transistor. This transistor falls under the NPN category and is available in the TO-92 plastic case.
What is a BC550 Transistor?
The BC550 is an NPN type general purpose low-power and low-frequency transistor where electrons are the majority charge carriers, emitted toward the PN junction from the emitter terminal of the transistor. This NPN transistor is available in three different versions like; BC550A, BC550C & BC550B. The maximum collector current of this transistor is 100mA with a maximum of 5V from the emitter to the base terminal. This transistor is used widely in amplification & switching applications within electronic circuits. This transistor is used widely for general-purpose applications within educational, hobby electronic projects & commercial appliances.
The BC550 NPN Transistor will be turned ON when a small amount of voltage is provided to the base terminal of the transistor. Once this transistor is biased, it allows 100mA of maximum current across the collector-emitter or CE Junction, known as the saturation region. In this condition, when a load that used above 100mA it damages the device. We know that this transistor is a current-controlled device. So the base current is detached then this transistor will turned off completely which is known as the cut-off region.
Whenever this transistor is used as a switch, then it handles up to 100mA of a load. The highest collector dissipation of this transistor is 500mW & the maximum DC current gain is approximately 800 so it can also be used as a preamplifier or a signal amplifier.
The pin configuration of the BC550 Transistor is shown below. This transistor has three terminals which are discussed below.
- Pin1 (Collector): This terminal collects electrons that are emitted from the emitter.
- Pin2 (Base): This terminal controls the transistor biasing.
- Pin3 (Emitter): As compared to the other two terminals of this transistor, the emitter terminal is doped highly. This terminal emits the electrons simply into the base terminal to control the number of electrons.
Features & Specifications:
The features and specifications of the BC550 Transistor are discussed below.
- The BC550 transistor is a Pb−Free device.
- This transistor is available within Package or Case TO-92-3 TO-226-3.
- The type of transistor is NPN.
- Its collector current maximum or IC is 100 mA.
- Its collector-to-emitter voltage or VCE maximum is 45V.
- Its emitter to base voltage or VEB maximum is 5V.
- Its collector-to-base voltage or VCB maximum is 50V.
- Its transition frequency or fT is 300 MHz.
- Its DC current gain or hFE ranges from 110 to 800.
- Its power dissipation or PD is 500 mW.
- Its operating and storage temperature ranges from -65 to +150 Centigrade.
- Its noise figure is – 1.2 dB.
- Its collector current is 0.1 A.
- The complementary PNP transistor of the BC550 transistor is the BC560. The SMD versions of this transistor are; BC847W (SOT-323), BC847 (SOT-23), BC850W (SOT-323) & BC850 (SOT-23). Equivalent or replacement of BC550 transistor is; BC547/BC546.
Turn OFF LED Circuit by Puff
Turn OFF LED circuit by Puff is shown below. This simple circuit is used to turn off the LED through a puff. When the puff is applied to the mic in this circuit is changed into a voltage whose voltage value is extremely small. This voltage can be amplified & provided to the circuit to turn off the LED.
The required components to make a turn OFF LED circuit by puff mainly include; an electret condenser mic, LED, NPN transistors like; BC550, BC337, BC327 PNP transistor, 5V battery, diode D1-1N4148, D2-Red LED, S1 push button, resistors R1-10K, R2-1M, R3-4.7K, R4-10K, R5-1K, R6-100, capacitors C1-100pF, C2-10uF and C3-100nF. Connect the circuit as per the circuit diagram shown below.
Once the connections are made, press the S1 push button. Once this button is pushed, both the Q2 & Q3 transistors which are connected as latching pairs will be activated, thus driving the LED to glow. Whenever you puff at the Mic in the circuit, the analog sound signal can be changed into a voltage signal. So this voltage signal is amplified through the Q1 transistor. This amplified signal can be provided to the latching pair transistors. So the transistor’s base will get the necessary voltage & BC327 PNP transistors stop conducting and LED will stop glowing. In order to switch it once more, need to press the ‘S1’ push button.
This puff LED circuit can be utilized as a candle. This circuit can be used in lanterns, stained glass lamps, haunted houses, model railroading accessories, spooky lighting, automotive novelties, and arts & crafts applications. This simple circuit is very useful as a decorative item to use in church during any special occasions.
The transistor can also be connected to a microcontroller and can be used for a whole lot of application. click here to know more on how to interface a transistor to microcontroller.
BC550 Transistor Applications
The applications of a BC550 transistor include the following.
- These transistors are used mainly for switching as well as amplification purposes.
- These types of transistors are used in the H-bridge, current mirror, oscillator, comparator, astable & bistable multivibrator circuits.
- These are used within impedance buffering & linear amplifiers.
- These NPN transistors are used within electronic circuits for pre-amplification stages.
- This transistor helps to drive loads < 100mA which can be used in different electronic circuits to drive LEDs, relays, ICs, power transistors, microcontrollers, etc.
- These are used in Darlington pairs.
- The emitter to base terminal voltage of this transistor is 5V only, so it can be utilized at the microcontroller’s output to drive loads.
- These are used for the amplification of signal, audio, and Preamplification.
- These are used for switching LEDs, relays, etc.
- These types of transistors are used in flashers or LED dimmers and Impedance buffering
- These are used within PWM-driven applications.
Selecting a transistor for a particular application is very significant based on different factors. To know more, please refer to this link for How to Select a Transistor.
Adding a resistor to the transistor’s base terminal is important to limit the excessive flow of current to the base terminal otherwise transistor can be damaged. To know more about this please refer to Choosing Base Resistance for Transistors in Electronic Circuits.
In any electronic circuit, transistor replacement has become necessary because of many reasons. To know more please refer to this link for Replacing Transistors in Electronic Circuits.
Please refer to this link for the BC550 Transistor Datasheet.
Thus, this is an overview of the BC550 transistor, pin configuration, specifications, circuit, working, and its applications. This is a very popular NPN-type BJT that belongs to the series BC547. Here is a question for you, what is a BC560 transistor?