BC547 is a general purpose BJT NPN transistor mostly used in electronics hobbyists and educational electronics projects. Besides these uses it can also be used in commercial circuits. It comes in TO-92 packaging and the maximum output current this transistor can handle is 100mA.
The transistor is having very good DC current gain and low noise capabilities due to which it is ideal to use in signal amplification stages. The typical saturation voltage is only 90 millivolts which is also a good sign to use it as a switch.
When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region as explained above. As discussed a transistor will act as an Open switch during Forward Bias and as a Closed switch during Reverse Bias, this biasing can be achieved by supplying the required amount of current to the base pin. As mentioned the biasing current should maximum of 5mA. Anything more than 5mA will kill the Transistor; hence a resistor is always added in series with base pin. The value of this resistor (RB) can be calculated using below formulae.
RB = VBE / IB
Where, the value of VBE should be 5V for BC547 and the Base current (IB depends on the Collector current (IC). The value of IB should not exceed mA.
A Transistors acts as an Amplifier when operating in Active Region. It can amplify power, voltage and current at different configurations.
Some of the configurations used in amplifier circuits are
- Common emitter amplifier
- Common collector amplifier
- Common base amplifier
Of the above types common emitter type is the popular and mostly used configuration. When uses as an Amplifier the DC current gain of the Transistor can be calculated by using the below formulae
DC Current Gain = Collector Current (IC) / Base Current (IB)
How to Safely Long Run in a Circuit
For long run in a circuit it is important to not increase load more than 100mA on it, and do not exceed the voltage across this transistor to 45V DC. Always use a suitable base resistor to provide required current for saturation. Do not use or store it in temperature above +150 centigrade and below -65 centigrade. Always confirm the collector emitter and base pins before placing in circuit. If accidently placed wrong in a circuit than check its performance again because placing wrong pins sometimes burns the internal circuitry of the transistor or make it weak.