Introduction to BC549
Hi Friends! I hope you’re well today. I welcome you on board. In this post, I’m going to discuss the Introduction to BC549. BC549 is a general purpose bipolar junction transistor that belongs to NPN transistor family. It contains three pins where small current change in one terminal produces a much large current change across other terminals. In other words, it is nothing but a current booster.
It is known as a low power low voltage current controlled device and is used for switching and amplification purpose. In this article I’ll be discussing complete details of BC549 transistor i.e. pinout, working principle, power ratings, physical dimensions and applications. Stay tuned.
Introduction to BC549
- BC549 is an NPN general-purpose bipolar junction transistor. It carries three pins named emitter, base, and collector and is available in TO-92 and SOT54 package.
- BC549 transistor contains three layers i.e. two N-doped layers and one P-doped layer. The P-doped layer stands between two N-doped layers. Plus, it contains two PN junctions where one is forward biased and the other is reverse biased.
- When no voltage is applied at the base terminal it is considered as grounded. In this case, the transistor acts like an open switch where both emitter and collector remain open.
- When voltage is applied at the base terminals it gets biased and draws current which is used to connect other terminals and current starts flowing from collector to emitter terminal.
- As this is an NPN transistor, here current flows from collector to emitter when voltage is applied, unlike PNP transistor where current flows from emitter to collector.
- Plus, both electrons and holes play a vital role in conductivity. In NPN transistor electrons are majority charge carriers and in PNP transistor holes are majority carriers.
- The movement of electrons, however, is faster than the movement of holes, the reason NPN transistors are better and faster than PNP transistors.
BC549 Pinout
BC549 comes with three pins named:
- 1: Emitter
- 2: Base
- 3: Collector
Following figure shows the pinout diagram of BC549.
- All three pins are used for external connections with other circuits. These pins are different in terms of operation and doping concentration.
- The collector voltage is larger than the base voltage and emitter terminal is highly doped compared to other terminals.
BC549 Pin Configuration
BC549 transistor can be employed in three main configurations as follows:
- Common emitter configuration
- Common base configuration
- Common collector configuration
Common emitter configuration is mostly used for amplification purposes as it contains the exact current and voltage ratings required for amplification.
- The amplification factor is called beta and is denoted by ß. It is mainly used to define the nature of amplification. It’s a ratio between collector current and base current. In BC549, the amplification factor ranges from 420 to 800.
- Another important factor is the current gain which is a ratio between collector current and emitter current. It is known as alpha and is denoted by a. The alpha value stands from 0.95 to 0.99 but more often than not its value is taken as unity.
BC549 Working Principle
- In BC549, emitter-base voltage is 5V which means when 5V is applied at the base terminal it gets biased and triggers the electron reaction.
- In the NPN transistor, the base terminal behaves like a control valve that controls the number of electrons.
- When voltage is applied at the base terminal, emitter starts emitting the electrons into the base terminal which controls the number of electrons. These emitted electrons passing through the base are collected by the collector terminal of the transistor.
- Moreover, the collector current is a mere 100mA i.e. you cannot drive heave loads using this transistor.
- As the only 5V is required to start the electron reaction at the base terminal, it can be easily employed across microcontrollers and microprocessors.
- When BC549 operates as an amplifier, small current as an input signal at the base terminal is used to induce a much bigger electric current at the other terminals.
- And when it works like a switch, it switches the small current at one part of the transistor into a much larger current across the other parts of the transistor.
- When transistor acts as a switch, it carriers two distinct states i.e. values are stored in the form of zero and one. Memory chip used in a computer is a common example of an electronic device that contains billions of transistors which can be turned on and off individually.
BC549 Power Ratings
Follow figure shows the absolute maximum rating of BC549:
- Emitter-Base voltage and Collector-Emitter voltages are 5V and 30V respectively.
- And Collector-Base voltage is 30V with collector current 100mA i.e. it cannot drive loads carrying ratings more than 100mA.
- The current gain ranges from 420 to 800 and transition frequency is 100MHz.
- These are stress ratings. Before you employ this transistor into your project and execute, make sure the ratings don’t exceed from absolute maximum ratings, else they will damage the product, and worse, your entire project, eventually.
- Also, if these ratings are applied for more than the required time, they can affect device reliability.
BC549 Alternatives
The following are the alternatives of a BC549 transistor.
The PNP complementary of BC549 are:
BC549 Applications
BC549 can be used in the following applications:
- Used in liner audio amplifiers.
- Employed in Darlington pairs and sensor circuits.
- Used in oscillator and comparator circuits.
- Finds application in current mirror circuits.
- Used in Astable and Bistable multivibrators.
- Used for impedance buffering and switching applications.
- Finds application in low noise stages in audio frequency equipment.
BC549 Physical dimensions
Follow figure shows the physical dimensions of BC549:
That’s all for today. Hope you find this article helpful. If you are unsure or have any question, you can approach me in the section below. I’d love to help you the best way I can. You’re most welcome to keep us updated with your valuable feedback and suggestions, they help us produce quality content. Thank you for reading this article.
Introduction to BC548
Hi Friends! Glad to see you here. I hope you’re well today. In this post, I’ll walk you through the Introduction to BC548. BC548 is a general-purpose transistor that falls under the family of NPN transistors. It carries three pins that are mainly used for external connection with the circuit. The small current at one terminal is used to control the large current at other terminals. Moreover, it can drive loads under 500mA and is available in TO – 92 package.
I suggest you read this post all the way through as you’ll get to know all nuts and bolts of BC548 transistor i.e. pinout, working principle, power ratings, applications, and physical dimensions. Let’s jump right in.
Introduction to BC548
- BC548 is an NPN general-purpose transistor, comes with three pins named emitter, base and collector.
- A small current at the base side is used to control large current at the collector and emitter terminals. The reason, it’s normally called a current controlled device.
- Decent current gain and power dissipation make it a suitable pick for amplification circuits and pre-amplification stages in other electronic applications. Moreover, it is also used as a switch to carry the load below 500mA.
- This BC548 transistor belongs to the NPN family where it contains three layers i.e. two N-doped layers and one P-doped layer. The P-doped layer is sandwiched between two N-doped layers.
- Also, it contains two PN junctions where one is reverse biased and the other is forward biased.
- The NPN transistor is like an electron valve where the base terminal controls the movement of electrons. It is widely used for amplification purposes in many electrical and electronics projects.
- Plus, electrons behave like majority carriers in NPN transistors whereas in PNP transistor holes behave like majority carriers. In conclusion, the mobility of electrons is better than the mobility of holes, thus NPN transistors are better and faster than PNP transistors.
1. BC548 Pinout
BC548 contains three pins named:
- 1: Emitter
- 2: Base
- 3: Collector
Following figure shows the BC548 pinout:
- All these terminals are different in terms of operation and doping concentration.
- The base terminal controls the current, emitter is used to emit the number of electrons when voltage is applied at the base terminal which is then collected by the collector.
- The small increase in input voltage applied at the base terminal produces a large change in output voltage across both collector and emitter terminals. This practice is used for amplification purposes.
- The emitter terminal is highly doped as compared to collector and base terminals. Plus, the collector voltage is larger than the base voltage.
2. BC548 Pin Configuration
BC548 transistor is used in three main configurations as follows:
- Common base configuration.
- Common emitter configuration.
- Common collector configuration.
Common emitter configuration carries exact voltage and current ratings mainly used for amplification.
- The amplification factor is used to define the nature of amplification. It is called beta and is denoted by ß. It is a ratio between collector current and base current. As it’s a ratio between the same factor i.e. current, it contains no unit. In this NPN transistor, the amplification factor ranges from 110 to 800.
- Similarly, the ratio between collector current and emitter current is called current gain and is mainly known as alpha, denoted by a. The alpha value lies between 0.95 to 0.99 but most of the time its value is taken as unity.
3. BC548 Working Principle
- When the base terminal is grounded, both emitter and collector terminals remain disconnected.
- When the voltage is applied at the base terminal, it gets biased, forming a bridge between collector and emitter.
- As this is an NPN transistor, the current will flow from collector to emitter, unlike PNP transistors where current flows from emitter to collector.
- Though both electrons and holes play a key role in conductivity, in the case of NPN transistors, electrons are major charge carriers.
- The base terminal controls the number of electrons passing from collector to emitter and appears positive with respect to the emitter terminal.
- The applied voltage at the base terminals draws a small current which is then used to police the large current at the collector and emitter terminals.
4. BC548 Power Ratings
The following figure shows the absolute maximum ratings of BC548:
- Collector-Base voltage is 30V. While Emitter-Base voltage and Collector-Emitter voltages are 5V and 30V respectively.
- The Collector current is 500mA with maximum power dissipation 625mW at temperature 25C.
- And the current gain ranges from 110 to 800.
- It’s important to note that these values are called stress ratings. Before you employ this transistor into the required circuit, make sure these ratings don’t cross the absolute maximum ratings, else you can risk your transistor and thus the entire project.
- Plus, if these ratings are applied for an extended period, they can influence the device reliability.
- Note: these values are measured at T = 25 C
5. BC548 Alternatives
The following are equivalent transistors of BC548:
They all belong to the NPN family. The PNP complementary of BC548 is BC558. The type of transistor you use depends on the ratings of load you intend to drive i.e. in case of BC548 you can drive loads under 500mA.
6. BC548 Applications
NPN type transistors are used in circuits when you intend to sink the current. BC548 is used in the following applications:
- Used in Darlington pairs to amplify weak signals.
- It can be employed in sensor circuits.
- Driving loads under 500mA.
- Used in audio amplification.
- Used in audio Amplifier Stages.
7. BC548 Physical dimensions
The following diagram shows the physical dimension of the BC548:
Recall, BC548 is a bipolar NPN junction transistor and is considered as a current-controlled device where small current at the base is used to control large current at the collector and emitter terminals. Plus, it can drive loads under 500mA and is available in TO – 92 package.
That's all for today. I hope you find this read helpful. If you have any question, you can approach me in the section below, I'd love to help you the best way I can. Feel free to keep us updated with your valuable feedback and suggestions. They help us create quality content. Thank you for reading this article.