BC547 is a general-purpose transistor mostly used in educational and electronics projects. It is also used in commercial circuits as well as in hobbies projects. It is a tiny three-terminal device capable to convert small signal inputs into large amplified outputs. It is a BJT (Bipolar Junction Transistor) NPN transistor that comes in TO-92 packaging and it can handle 100mA output current. The transistor, BC 547 is shown below.
BC547 Transistor Features
- Package-Type: TO-92
- Bi-Polar NPN Transistor
- DC Current Gain (HFC) is 800 maximum
- Max Collector current (IC) is 100mA
- Max Emitter Base Voltage (VEBO) is 6V
- Max Collector-Base Voltage (VCB): 50V
- Base Current(IB) is 5mA maximum
BC547 as Switch
In a switch, it is operated in the Saturation and Cut-Off Region. A transistor acts as an Open switch during forwarding and as a Closed switch during Reverse Bias, this biasing can only be achieved by supplying the required amount of current to the base pin of the transistor. As mentioned above the biasing current maximum of 5mA. More current than 5mA will kill the Transistor; so, a resistor is always be added in series with base pin. We can calculate the value of resistor (RB) using below formulae.
RB = VBE / IB
BC547 as Amplifier
A transistor acts as an Amplifier while operating in Active Region. BC547 can amplify power, voltage, and current at different configurations.
Some configurations used in amplifier circuits are
- Common collector amplifier
- Common emitter amplifier
- Common base amplifier
The formula used for the amplifier: DC Current Gain = Collector Current (IC) / Base Current (IB)
The complementary of BC547 is PNP BC557.
Replacement and Equivalent:
You can replace bc 547 with 2N2222, 2N3904, 2N4401, BC337. The Pin configuration of some transistors is different from BC547 so check pin configuration before replacing in a circuit.
A lot of applications associated with BC547, a few of the main applications are given below.
- Sensor Circuits
- Audio Preamp circuits
- Audio Amplifier Stages
- Switching Loads under 100mA
- Transistor Darlington Pairs
- Radio Frequency Circuits
How to Protect Transistor:
For the long life of bc547 do not increase load more than 100mA on it, and do not exceed the voltage across this transistor to 45V DC. Always use a relevant base resistor to provide the required current for saturation. The temperature does not above +150 centigrade and below -65 centigrade. Always confirm the collector-emitter and base pins before placing them in the circuit. If accidentally placed wrong in a circuit than check its performance again because wrong input can decrease its efficiency.